a. Epidemiology of primary hyperoxaluria, including primary hyperoxaluria 1, primary hyperoxaluria 2, and primary hyperoxaluria 3

PH is a rare genetic disorder of overproduction of oxalate in the liver, resulting in long-term accumulation of oxalate and urea in kidneys, subsequently producing chronic kidney disease and renal failure. This genetically inherited disorder is rare, with an incidence rate of approximately 1 to 2 cases per 100,000 in the US population (Shah et al., 2023) and 1–3 cases per 100,000 in the European populations (Cochat et al., 1995; Kopp and Leumann, 1995; van Woerden et al., 2003). It is also reported to be more predominant in countries where consanguineous marriages are common, particularly in regions of Northern Africa and the Middle East (Soliman et al., 2022). There are 3 types of PH: PH1, PH2, and PH3. PH1 is the most common and rapidly progressing disorder of the three, accounting for the majority (up to 80%) of the reported PH cases (Bhasin et al., 2015).

b. Symptoms of primary hyperoxaluria

PH results in nephrolithiasis, urolithiasis, and high levels of oxalate in the kidneys. This chronic kidney disease is the outcome of renal calcium oxalate accumulation, ultimately leading to frequent stone formation and kidney failure (Ermer et al., 2016). As kidney failure progresses, the accumulation of oxalate may spread to other organ systems. Although symptoms may appear at any age, typically they tend to appear in childhood. Just like many other diseases, symptoms and progression of PH may differ from patient to patient. Symptoms associated with PH1 include failure to thrive, oxalate deposits in the kidney, formation of kidney stones in the urinary tract, dysuria, hematuria, and frequent urinary tract infections (Ermer et al., 2016). PH1 usually develops during childhood and progresses during adulthood, leading to chronic kidney disease and end-stage renal failure. PH2 also usually develops during childhood, but it presents itself with milder symptoms, accounting for less than 10% of all PH cases (Ermer et al., 2016). PH2 can also progress to cause kidney failure, although that occurs much later in life as compared with the rapid progression of PH1. Symptoms of PH3 also begin in childhood and can be like those who have PH1 or PH2; however, they are much milder. Due to the rareness of the PH3 disorder, not much can be concluded about its progression. The occurrence of kidney failure and nephrocalcinosis is very rare, with less prevalence of kidney and urinary stones in patients who have PH3 (Singh et al., 2022).

c. Genetic causes of primary hyperoxaluria 1, primary hyperoxaluria 2, and primary hyperoxaluria 3

These disorders result from defects in various enzymes that are involved in the metabolism of glyoxylate. Oxalate is an end product of the metabolism of some diet-derived nutrients in the liver, which is normally excreted from the body via the kidneys. The small amounts of oxalate that the liver generates under normal conditions can be successfully eliminated by the kidneys. However, when the liver produces excessive oxalate, this results in its accumulation in the kidneys leading to nephrocalcinosis and kidney failure (Ermer et al., 2016). This occurs due to defects of certain enzymes in the liver that are responsible for regulating the production and excretion of oxalate.

PH1 is caused by genetic alterations in the alanine-glyoxylate aminotransferase (AGXT) gene, which leads to a deficiency in the expression of this enzyme (Tarn et al., 1997). When present at normal levels, this enzyme converts glyoxylate to glycine. The absence of the AGXT enzyme leads to accumulation of glyoxylate and overproduction of oxalate by lactate dehydrogenase (Tarn et al., 1997). Glyoxylate can also be reduced to glycolate using NADH or NADPH by the enzyme glyoxylate reductase (GR). PH2 results from a mutation of the glyoxylate reductase-hydroxypyruvate reductase (GRHPR) gene, which encodes the enzyme GR (Cregeen et al., 2003). The lack of GR can contribute to further increase in the levels of oxalate in cytosol. PH3 results from a defect in the 4-hydroxy-2-oxoglutarate aldolase (HOGA1) gene (M’dimegh et al., 2017). A deficiency of this gene leads to a loss of production of its enzyme HOGA1, which favors the conversion of 4-hydroxy-2-oxoglutarate (HOG) to pyruvate and glyoxylate. The exact mechanism of how a deficiency in the HOGA1 gene causes accumulation of oxalate resulting in PH3 remains unclear (Bar et al., 2021).

d. Current treatment options of primary hyperoxalurias

Changes to low-salt and restricted diets in oxalates may help to lower the levels of oxalate in urine (Mitchell et al., 2019). Calcium supplements are the primary medical treatment of PHs when they are taken with meals (Takei et al., 1998). Interaction of oxalate with calcium in the gut could limit the intestinal absorption of oxalate and promote its fecal excretion. Prescription of vitamin B-6 can help reduce oxalate in the urine in some PH patients (Hoyer-Kuhn et al., 2014). Other medications, which may help to reduce oxalate in the body, include thiazide diuretics (Vigen et al., 2011) and phosphates and citrate (Krieger et al., 2015). However, these medications can only slow down the progression of PHs, not cure the disease.

When kidney failure caused by kidney stones in PH patients becomes severe, dialysis and kidney transplantation can be performed to treat PH, however, kidney stones may reappear post transplantation due to dysfunction of the liver that consistently produces excessive oxalate (Cornell et al., 2022). Simultaneous kidney and liver transplantation may be the only treatment that might cure some types of PHs (Cornell et al., 2022) until the recent development on siRNA therapeutics.

e. Treatment of primary hyperoxaluria 1 with the small interfering RNA drug lumasiran and treatment of PH1, PH2, and PH3 with a potential small interfering RNA drug, nedosiran

In November 2020, The FDA approved lumasiran as the first medication possible to cure PH1 disease for pediatric and adult patients (Scott and Keam, 2021). Lumasiran (brand name Oxlumo) is a siRNA drug developed by Alnylam Pharmaceuticals with a double-stranded chemical-modified ribonucleic acid conjugated to GalNAc for liver-specific delivery (sequence and chemical modifications are shown in Fig. 3). By targeting on the 3′-UTR region of hydroxy acid oxidase 1 (HAO1) mRNA (Fig. 4), lumasiran works by reducing the HAO1 mRNA, leading to lower levels of glycolate oxidase (GO) enzyme in hepatocytes (D’Ambrosio and Ferraro, 2022). The reduced GO enzyme results in increased levels of glycolate and decreased levels of oxalate in the liver, kidneys, and urine. Lumasiran is administered subcutaneously with three loading doses (6 mg/kg) once monthly and maintenance doses (3-6 mg/kg) once every 3 months.

As shown in Table 1, the pharmacokinetics (PK), pharmacodynamics (PD), safety, and tolerability of lumasiran were determined in a single blind, placebo-controlled phase 1/II study (NCT02706886) with 32 healthy and 20 pediatric and adult patients with PH1. The study concluded that lumasiran had an acceptable safety profile with no serious adverse drug reactions (ADRs), and all patients with PH1 had reduced urinary oxalate excretion to near-normal levels (Frishberg et al., 2021). The efficacy of lumasiran was further confirmed in a randomized, double blind, placebo-controlled phase 2 study (NCT05161936) using adult patients with recurrent oxalate kidney stones and elevated urinary oxalate levels.

Lumasiran earned the FDA’s approval due to the positive results found in several phase 3 studies, including ILLUMINATE-A NCT03681184 (Garrelfs et al., 2021), ILLUMINATE-B NCT03905694 (Sas et al., 2022; Hayes et al., 2023), and ILLUMINATE-C NCT04152200 (Michael et al., 2023). These studies further verified that lumasiran resulted in substantial reductions in plasma and urine oxalate levels with acceptable safety in patients with PH1 who have advanced kidney disease. With only 2 and half years on the market, it may be too soon to have real-world studies to evaluate the PK, PD, and safety of lumasiran in the treatment of PH1, but lumasiran has been considered as a turning point in the management of PH1 (D’Ambrosio and Ferraro, 2022).

Due to targeting HAO1 mRNA and GO enzyme, lumasiran is only effective in the treatment of PH1. Pharmacologic options are not available yet for the treatment of PH2 and PH3. The situation may be changed in the near future with the development of a candidate siRNA drug, nedosiran, for the treatment of all types of PH (Liu et al., 2022).

Under development by Dicerna Pharmaceuticals, nedosiran is a candidate siRNA drug with chemical modifications and GalNAc conjugation. By targeting the lactate dehydrogenase mRNA, nedosiran could reduce levels of lactate dehydrogenase enzyme, a key enzyme mediating the final step of the production of oxalate from glyoxylate in the liver, ultimately resulting in reducing the formation of oxalate in all three types of PH.

As shown in Table 1, the PK, PD, safety, and tolerability of nedosiran have been assessed and will be continually determined through various clinical studies from phase 1 to 3, including PHYOX1 (NCT03392896), a phase 1 study with healthy volunteers and PH patients; PHYOX2 (NCT03847909), a pivotal randomized phase 2 study with PH1 and PH2 patients (Baum et al., 2023); PHYOX4 (NCT0455486), a phase 1 study with PH3 patients (Goldfarb et al., 2023); PHYOX7 (NCT04580420), a phase 2 study with patients with PH1/2 and end-stage renal disease; PHYOX8 (NCT05001269), a phase 2 study with pediatric patients with PH and relatively intact renal function; and PHYOX3 (NCT04042402), a long-term extension phase 3 study with patients with PH1, PH2, and PH3. In the PHYOX2 study, the PH1 subgroup maintained a sustained reduction of urine oxalate levels, whereas no consistent effect was seen in the PH2 subgroup (Baum et al., 2023). In the PHYOX4 study, nedosiran was well tolerated without safety concerns, and a trend toward urinal oxalate lowering was observed in PH3 patients with nedosiran (Goldfarb et al., 2023). The results from the other ongoing clinical studies have not been released yet. Whether nedosiran can treat all types of PH needs to be tested in more PH2 and PH3 patients, pediatric patients, and patients with renal impairment before the drug can receive FDA approval.

In conclusion, although rare, PH patients may suffer severe kidney failure at any given time if the disease is not appropriately managed. Currently, treatment options may slow down disease progression, but without targeting the origin of the disease in the liver for excessive production of oxalate, the disease cannot be cured, and severe kidney failure can occur. The siRNA drug lumasiran has become the only FDA-approved medication with the potential to cure PH1 disease, and nedosiran has the potential to be developed as a siRNA drug to treat all types of PH diseases.

a. Epidemiology of familial hypercholesterolemia

People with FH are unable to sufficiently metabolize LDL cholesterol (LDL-C). They are thus more likely to develop ASCVD early in life if preventative lifestyle and pharmacologic measures are not taken. Up to 400 people in 100,000 are affected by FH, which is the most common monogenic disorder associated with ASCVD (Lui et al., 2021). Females and males are equally affected by this condition as it is caused by genetic differences that can be passed down at an equal rate in 50% by both sexes. It is more common in African ethnicities and less common in Asian groups. Latino and White populations fall in the middle (Toft-Nielsen et al., 2022). There is no significant difference in prevalence between children and adults. It should be noted that most studies done on FH occur in the Western high-income countries, so data are lacking on a global scale (Hu et al., 2020b).

b. Symptoms of familial hypercholesterolemia

FH is usually diagnosed by blood tests. Clinical findings indicative of FH include elevated total cholesterol and LDL-C and premature coronary heart disease. In homozygous FH, premature coronary heart disease can occur before the age of 20. On a physical exam, patients with FH may have arcus corneae, xanthelasma, tendon xanthomas, or tuberous xanthomas (Pejic, 2014).

c. Genetic causes of familial hypercholesterolemia

FH is a genetic disorder that is autosomal dominant. Carriers of the disease may inherit one or two alleles, making them heterozygous or homozygous, respectively. Homozygous FH is much rarer than heterozygous, manifesting in an approximately 1 in 100,000 to 1,000,000 individuals (Nohara et al., 2021), and is also the more extreme of the two (Cuchel et al., 2014). The most common mutations affecting the LDL-R gene are found in 80%–85% of cases. It is possible that apolipoprotein B (APOB) and proprotein convertase subtilisin/kexin type 9 (PCSK9) genes may be affected in rarer cases, accounting 5%–10% and 2% of cases, respectively (Pejic, 2014). The least common mutations are in the LDL-R adaptor protein 1 (LDLRAP1) gene. In other cases, clinically diagnosed FH patients do not have mutations in these genes. These patients are considered mutation negative, and the disease state may be due to polygenic causes instead (Benito-Vicente et al., 2018). The affected genes directly impact FH presentation. If LDLR is the mutated gene, plasma LDL-C levels are higher than if APOB or PCSK9 are affected. The most severe presentation is found if LDLR is affected (Lui et al., 2021).

d. Current treatment options for familial hypercholesterolemia

Lifestyle changes are the first recommendation for FH patients who must lower their LDL-C, but this by itself is not usually sufficient. For example, patients with FH are recommended to exercise regularly and refrain from smoking. Patients with comorbid conditions should be treated with standard therapies for those comorbidities. Examples of common comorbidities that can add risk for FH are hypertension and diabetes mellitus (McGowan et al., 2019). These lifestyle changes should be continued throughout pharmacological treatment of the best quality of life.

The first choice of most prescribed medications for FH is statins. Statins work by inhibiting b-hydroxy b-methylglutaryl-CoA reductase, preventing the step in the pathway leading to the production of cholesterol in the liver. Preventing cholesterol production in the body reduces LDL-C concentrations in the blood. The most common ADRs of statins are muscle pain and weakness (Benito-Vicente et al., 2018). The ADRs are more common among the high-intensity statins, atorvastatin 4–80 mg and rosuvastatin 20–40 mg. However, the high-intensity statins are the most efficacious for lowering LDL-C up to 50%–60%. Thus, they are recommended above other statins if tolerable to the patient (McGowan et al., 2019).

Niacin, bile acid sequestrants, and ezetimibe are also prescribed for the treatment of FH, often added onto statin therapy when not sufficient as monotherapy (Sjouke et al., 2011). Niacin impairs cholesterol and triglyceride synthesis. It may cause vasodilation and increased hepatic enzymes. Bile acid sequestrants complex with micelles made of bile acid and cholesterol, causing them to be excreted instead of absorbed. This reduces overall cholesterol levels and thus LDL-C. Bile acid sequestrants, such as colesevelam, may be effective, but they can also decrease the intestinal absorption of fat-soluble vitamins, which is a concern with their use. Ezetimibe blocks cholesterol uptake by inhibiting Niemann-pick C1-like 1 protein. This reduces cholesterol absorption through the intestine, lowering overall cholesterol content and LDL-C (Benito-Vicente et al., 2018).

A newer type of parenteral treatment of FH is human monoclonal antibodies. Alirocumab and evolocumab target PCSK9 protein, which normally breaks down LDL-R. Decreasing PCSK9 increases LDL-R so that more LDL-C can be taken up and brought to the liver for digestion. These have been used as monotherapy or in combination with other treatments and are well tolerated (McGowan et al., 2019). However, some patients end up with fatigue, muscle pain/soreness, and swelling near the injection site. There is an uncommon, but possible, risk of kidney and liver problems with these medications (Jhaveri et al., 2017).

e. Treatment of familial hypercholesterolemia with an antisense oligonucleotide drug mipomersen and a small interfering RNA drug inclisiran

a. Epidemiology of acute hepatic porphyria

AHP is a group of four genetic disorders caused by a defect in an enzyme involved in the heme biosynthesis pathway. The four different types of AHP are acute intermittent porphyria (AIP), hereditary coproporphyrin (HCP), variegate porphyria (VP), and δ-aminolaevulinic acid dehydratase deficiency porphyria (ADP) (Balwani et al., 2017). These defects cause repeat acute neurovisceral attacks that severely affect the patient’s mental and physical health. Precipitating factors induce the heme synthesis pathway through the rate-limiting enzyme, δ-aminolaevulinic acid synthase 1 (ALAS1), which produces an accumulation of the heme precursors aminolaevulinic acid (ALA) and porphobilinogen (PBG) in the liver, which then circulate through the rest of the body (Gouya et al., 2020). These intermediates are toxic at high levels, causing injury to the nervous system and a wide array of clinical manifestations.

AHP is considered a rare group of diseases and has a global prevalence of 5 per 100,000 individuals (de Souza et al., 2021). In the United States, less than 200,000 people are affected by AHP. The most common type is AIP, accounting for 80% of the total symptomatic cases of AHP (Balwani et al., 2020). Approximately 1 in 1600 Caucasians have mutations in the gene that causes AHP, but the penetrance among carriers is 1% in the general population and up to 50% in families with a history of the disorder (Balwani et al., 2020). AIP affects women significantly more than men, attacks most commonly begin postpuberty, and it recurs until menopause (de Souza et al., 2021). Founder effects in Scandinavia, southeast of Spain, and South Africa result in greater prevalence in these regions (Bonkovsky et al., 2019; de Souza et al., 2021). ADP is the rarest form of AHP and has only eight documented cases worldwide, with all of them being males (Mohan and Madan, 2022).

b. Symptoms of acute hepatic porphyria

All four AHP types present with acute attacks of pain due to central, peripheral, and autonomic nervous system dysfunction. The most common symptoms are abdominal pain, nausea and vomiting, constipation, hypertension, and tachycardia. Those who suffer from AHP often experience peripheral neuropathy like muscle pain and weakness, especially in the back, arms, and legs. Anxiety, delirium, hallucinations, insomnia, and seizures are neurologic symptoms that are also common among all forms of AHP (Bonkovsky et al., 2014; Ramanujam and Anderson, 2015). Patients are found to have reddish brown urine due to the oxidation of porphobilinogen to uroporphyrin (Bissell and Wang, 2015). Most heterozygotes of AIP remain asymptomatic or only experience one or a few attacks, but 5% of patients have four or more recurrent attacks per year. Those who suffer from AIP also have an increased risk for hepatocellular carcinoma, chronic hypertension, and end-stage renal disease (Ramanujam and Anderson, 2015). ADP presents similar severity to AIP, with the same neuropsychiatric and neuropathic symptoms with abdominal pain (Mohan and Madan, 2022). HCP and VP are less prevalent and less severe than AIP, although the symptoms during attacks are indistinguishable from AIP, other than the cutaneous manifestations like blistering skin lesions, bullae, erosions, ulcers, and milia. VP and HCP exhibit skin manifestations due to the buildup of photosensitizing porphyrins in the skin and blood vessels (Ramanujam and Anderson, 2015; Kothadia et al., 2022). There are several factors that can trigger these symptoms, including weight loss, surgery, anesthesia, environmental and lifestyle stressors like smoking and alcohol, diabetes, porphyrinogen drugs, and emotional stress (Bissell and Wang, 2015). AHP is an inherited group of diseases, but many individuals who have causing mutations do not experience clinical manifestations unless affected by these different risk factors. Symptoms can be difficult to attribute to AHP because they are nonspecific, which causes delays in diagnosis (Bonkovsky et al., 2014).

c. Genetic causes of acute hepatic porphyria

AHP is caused by genetic mutations in the genes of heme synthesis. Missense, nonsense, or other mutations in these genes in combination with environmental, nutritional, and hormonal factors lead to a serious decrease in heme and upregulation in ALAS1. AIP, HCP, and VP are autosomal dominant disorders. AIP is caused by a defect of the hydroxymethylbilane synthase (HMBS) gene, which leads to a deficiency in the enzyme porphobilinogen deaminase (Chen et al., 2016). HCP corresponds to a variant in the coproporphyrinogen-III oxidase (CPOX) gene that causes a defect in the enzyme coproporphyrinogen oxidase (Hasanoglu et al., 2011). VP is caused by a deficiency in the enzyme protoporphyrinogen oxidase due to a variant in the protoporphyrinogen oxidase (PPOX) gene (Whatley et al., 1999). Heterozygous carriers with defects in HMBS, CPOX, or PPOX genes have reduced enzyme activities to 50%, which does not cause a substantial deficiency of heme unless stimulated by precipitating factors. In ADP, enzyme activities are even lower due to both alleles being affected (Ramanujam and Anderson, 2015). Homozygous or compound heterozygous deficiencies of the affected enzymes in AIP, HCP, and VP are usually lethal in utero; very few children survive into adulthood due to extreme problems with the nervous system. ADP results from an abnormal activity of ALA dehydrase (ALAD) due to abnormal expression coded by the ALAD gene. ADP is an autosomal recessive disorder, which can cause either a heterozygous or homozygous deficiency of ALAD (Jaffe and Stith, 2007). Heterozygotes of the disorder are clinically asymptomatic (Bonkovsky et al., 2019).

d. Current treatment options for acute hepatic porphyria

Treatment of AHP primarily consists of identifying and avoiding the risk factors that induce attacks. Without exposure to precipitating factors, the heme biosynthesis pathway may not be activated, and attacks can be prevented. A patient would be screened for possible medications, for instance hormonal contraceptives, or underlying conditions like infection that could pose as precipitating factors. Smoking and alcohol should be avoided, and a patient’s dietary history should be reviewed (Anderson, 2019). If avoiding these triggers is not enough for patients who experience mild cases of attacks, then glucose overload therapy is an option. Glucose is administered as tablets or concentrated dextrose solutions in the initial stages of an attack (Balwani et al., 2017). For those who do not respond to glucose overload or experience more severe cases of attacks, hemin-based therapy (Panhematin or Normosang) is the next available option. ALAS1 is downregulated by the hemin groups that are taken by hepatocytes, which are oxidized iron protoporphyrin IX molecules. This results in the inhibition of ALA and PBG production, which inhibits clinical manifestations. Hemin is given daily for 4 to 5 days during an attack, and scheduled prophylactic infusions are most often given weekly or biweekly for prevention depending on the patients. This is because the effect of heme on ALAS1 only lasts 1 week, so repeated treatment is required for lasting effects (de Souza et al., 2021). Due to the hemin containing a significant amount of iron by weight, frequent infusions can lead iron overload to cause hepatic damage and fibrosis (Balwani et al., 2017). Hemin is often found to cause acute ADRs like headaches, fevers, and phlebitis, as well as chronic ADRs such as venous thrombosis, venous obliteration, and central venous catheter complications (Ventura et al., 2022). In some cases, women experience cyclic attacks due to hormone fluctuations from menstrual cycles, which can be managed with gonadotropin-releasing hormone or luteinizing-releasing hormone and is initiated in first few days of the cycle (de Souza et al., 2021). Liver transplantation has been found successful in extreme cases as the last resort for patients who experience severe debilitating attacks that do not respond to hemin therapy (de Souza et al., 2021).

e. Treatment of acute hepatic porphyria with the small interfering RNA drug givosiran

Givosiran, sold under the brand name Givlaari, was developed by Alnylam Pharmaceuticals to treat adults with AHP, which was approved by the FDA in November 2019 (Scott, 2020). Treatment with givosiran helps to reduce attacks, pain, and hemin use to improve the lives of patients with AHP. Givosiran is a double-stranded siRNA (sequence and chemical modifications on each nucleotide are shown in Fig. 3) targeting exon 5 of the ALAS1 mRNA (Fig. 4) to reduce production of ALAS1 protein in the liver (Majeed et al., 2022). Givosiran is covalently linked to a ligand containing three GalNAc residues that help directly to bind to ASGPR found on the membrane surface of hepatocytes, resulting in high specific delivery to the liver. After entering the hepatocyte, givosiran silences the ALAS1 mRNA through the RISC-mediated RNAi mechanism and reduces heme biosynthesis (de Souza et al., 2021). Givosiran is chemically modified with the addition of a 2’-deoxy-2’-F or a 2’-Ome group in the ribose sugar moieties, and PS linkages at the 5′ end of the siRNA strands to help prevent nuclease digestion of the siRNA stands (Majeed et al., 2022). It is administered once monthly by subcutaneous injection in a dosage of 2.5 mg/kg.

As shown in Table 1, the PK, safety, and tolerability of givosiran were first established in a phase 1 study (NCT02452372) with 40 participants with AIP. The study found that common ADRs included tolerable nasopharyngitis, abdominal pain, and diarrhea, and serious ADRs occurred in 15% of patients (Sardh et al., 2019). The long-term safety and efficacy of givosiran were further determined in a phase 1/2 study with AIP patients (NCT02949830). Givosiran resulted in reduced ALAS1 mRNA levels, nearly normalized levels of the neurotoxic intermediates, and a lower attack rate.

The phase 3 trial leading to the FDA’s approval is ENVISION (NCT03338816), a study to evaluate the long-term efficacy and safety of givosiran using 94 patients with AHP in a 6-month, double blind, randomized, placebo-controlled period (Balwani et al., 2020; Wang et al., 2022). Eligible patients had to be older than 12, have a confirmed genetic diagnosis of AHP and elevated levels of urinary ALA or PBG, and had at least two attacks within 6 months prior to the start of trial that required hospitalization or treatment with hemin. Half of the patients were given monthly givosiran (2.5 mg/kg) and the other half placebo for 6 months. Of the 94 patients with AHP, the annualized rate of composite porphyria attacks was 74% lower than the placebo group as well as reduced fasting levels of PBG and ALA. Additionally, greater than 50% of the patients did not receive hemin infusions. Givosiran-treated patients experienced reduced pain and less analgesic use, as well as improvement in physical health, mental health, and general quality of life. ADRs were experienced by both the givosiran and placebo groups. There were elevations in serum aminotransferase levels, 15% in the givosiran group and 2% in the placebo, which resolved by itself in most patients with continuous treatment. Only one patient was permanently discontinued from the trial due to persistently elevated ALT values. Additionally, there were renal adverse events such as increases in serum creatinine levels and decreases in estimated glomerular filtration rate, 15% in the givosiran group and 7% placebo, but were overall considered temporary. Approximately 25% of givosiran-treated patients faced mild injection site reactions (Balwani et al., 2020).

Before the approval of givosiran, hemin was the only FDA-approved therapy for AIP attacks in the United States (Blaylock et al., 2020). Givosiran has shown potential to significantly reduce the annualized rate of porphyria attacks as well as improved several other outcomes, including hemin use and pain (Syed, 2021). With only 3 years on the market, no real-world study on the usage of givosiran has been published yet. By directly targeting ALAS1 and heme biosynthesis, givosiran may become the first therapeutic agent for curing AIP disease. However, although generally well tolerated acceptable safety profile was defined in the clinical trials, givosiran may still increase the risk of hepatic and kidney toxicity, which needs to be monitored carefully during treatment.

a. Epidemiology of hereditary transthyretin amyloidosis

hATTR is one of the most frequently researched SDLO due to its debilitating consequences and extrahepatic manifestations. Multiple aspects can be factored into the epidemiology of hATTR, such as location, ethnicity, age, and gender. The prevalence of hATTR is relatively low, with only approximately 50,000 patients (5 to 6 per 100,000) diagnosed worldwide (Hawkins et al., 2015). Of this number, approximately 10,000 patients have polyneuropathy, and about 40,000 patients have cardiomyopathy. In endemic areas like Portugal, Sweden, and Japan, incidence as high as 1 in 1000 has been reported (Hawkins et al., 2015). In Portugal, the location where hATTR was first diagnosed and researched, the prevalence is higher, with 1 in every 538 individuals having the condition. France and Brazil have also been named endemic areas in some studies due to moderate incidence, but they are not as populated with hATTR patients compared with Portugal, Sweden, and Japan. In the United States, hATTR has been diagnosed in about 6400 individuals, and those of European descent are at a greater risk of being affected (Schmidt et al., 2018). As healthcare technology, disease awareness, and genetic counseling advance, it is expected that the global number of reported cases will increase (Luigetti et al., 2020). Disease onset has been found to occur earlier in males compared with females, but the overall incidence is equivalent in both genders. All races and ethnicities are prone to hATTR, but there may be a higher frequency among Irish and African American patients. Although age of disease onset could vary based on each individual and the type of mutations that they have, a previous study has shown that hATTR is most evident in middle- to older-aged adults (Luigetti et al., 2020).

b. Symptoms of hereditary transthyretin amyloidosis

Signs and symptoms of hATTR can really vary from one individual to the next in terms of being mild or severe. Initial symptoms of hATTR include shortness of breath, numbness, swelling in the legs or ankles, bloody diarrhea, constipation, inflamed rippled tongue, easy bruising, and fatigue. As hATTR progresses, these symptoms can worsen and cause complications that require immediate medical attention. Peripheral polyneuropathy is one of the major systemic manifestations that includes both somatic and autonomic impairment. Common symptoms of autonomic neuropathy include orthostatic hypotension, sexual dysfunction, diaphoresis, and urinary tract infections. Somatic neuropathy is associated with voluntary movement dysfunction that progresses from a distal to proximal direction (Luigetti et al., 2020). In fact, hATTR with polyneuropathy has been categorized into different stages based on symptoms and need for assistance, with stage 0 being the least severe and stage 3 being the most severe (Hawkins et al., 2015). Patients can also present with serious cardiac, ocular, central nervous system, gastrointestinal, and renal manifestations. Examples include glaucoma, amyloid deposition on the iris or lens, conduction blocks, arrythmias, headaches, seizures, proteinuria, renal failure, unintentional weight loss, and carpal tunnel syndrome (Luigetti et al., 2020). Like polyneuropathy, cardiomyopathy is a common manifestation of hATTR, which can be accompanied by ventricular wall thickening, arrythmias, abnormal diastolic blood pressure, and heart failure (Hawkins et al., 2015).

c. Genetic causes of hereditary transthyretin amyloidosis

hATTR has a genetic basis and is characterized by the dissociation and misfolding of TTR protein, leading to abnormal deposition of amyloid fibril aggregates throughout the body. TTR protein, in its wild-type form, is responsible for transporting thyroxine and vitamin A along with retinol binding protein through circulation. TTR is a tetramer with each subunit containing 127 amino acids. Once dissociated, monomers contain eight antiparallel β-pleated sheets. This condition is typically classified as per two major systemic manifestations, polyneuropathy or cardiomyopathy, also known as familial amyloidotic polyneuropathy or cardiomyopathy, respectively (Ruberg and Berk, 2012). The major site of TTR protein synthesis is the liver, whereas smaller amounts come from the choroid plexus and retina.

The symptoms and patterns of hATTR distribution can be attributed to the genetic mutations in the TTR gene on chromosome 18, which contains four exons and three introns. hATTR has long been known to have a genetic cause; as research progresses and additional patient populations are discovered, new mutations continue to be identified. Currently, there are about 120 variants of the TTR gene that contribute to the disease (Luigetti et al., 2020). The most common mutation, Val30Met, is the point mutation at position 30, which results in the incorrect substitution of methionine instead of valine. This variant accounts for a significant percentage of the hATTR phenotypes around the world, most notably polyneuropathy in the endemic area of Portugal. Other mutations in the TTR gene can result in a mixed phenotype of polyneuropathy and cardiomyopathy or cardiomyopathy alone (Luigetti et al., 2020). The Val122Ile mutation results in mainly cardiomyopathy (Hawkins et al., 2015). The highest frequency of this mutation is seen in the African American population, whereas a greater percentage of European descendants are affected by the Val30Met mutation. These point mutations are inherited in an autosomal dominant pattern, which means both homozygous and heterozygous genotypes can cause hATTR. Since the TTR gene is located on an autosomal chromosome, there is no significant difference in the inheritance between male and female. However, the gender of the parents from whom the mutation is inherited can influence disease onset. A male child inheriting the mutation from his mother is at risk of early onset, whereas a female child inheriting the mutation from her father has conferred protection against the disease. Due to the autosomal dominant pattern of the disease, family members of any affected individual have a high risk of being carriers of the variant and should receive adequate genetic counseling as soon as possible (Luigetti et al., 2020).

d. Current treatment options for hereditary transthyretin amyloidosis

Current treatment options for hATTR are limited to symptomatic management, liver transplantation, and TTR-stabilizing drugs. Due to the multisystem involvement of this disease, management often involves a multifaceted approach. Patients are first started on symptomatic treatment of control of common mild systemic manifestations (Luigetti et al., 2020). These treatments can be a mixture of both nonpharmacologic and pharmacologic interventions like 9-α fludrocortisone, pacemaker implantation, or dialysis (Plante-Bordeneuve, 2014). More serious manifestations like polyneuropathy and cardiomyopathy require specific treatment plans with either orthotopic liver transplantation or TTR tetramer–stabilizing drugs.

For many patients, liver transplantation continues to be the first-line treatment. As per a retrospective analysis conducted by the Familial Amyloidotic Polyneuropathy World Transplant Registry, the 20-year survival rate after liver transplantation is 55.3% (Ericzon et al., 2015). Transplantation replaces the TTR gene mutations and allows wild-type TTR protein to be synthesized (Luigetti et al., 2020). This therapy is effective, with up to a 98% reduction in the mutant TTR protein (Hawkins et al., 2015). There are, however, some complications and disadvantages. Liver transplantation only prevents additional production of mutant TTR. So, preformed amyloid fibrils in the other organs could still induce newly synthesized wild-type TTR protein to dissociate and form aggregates as mutant TTR protein would. This phenomenon is referred to as “seeding” (Luigetti et al., 2020). There are also several adverse events associated with transplantation, such as hepatic artery thrombosis, increased risk of infection, and post-transplant lymphoproliferative disorder (Hawkins et al., 2015). Although there are benefits of liver transplantation, pharmacologic agents are needed as safer alternatives that are less invasives than tissue transplantation.

There are two main TTR stabilizers used in practice: tafamidis (brand name Vyndamax or Vyndaqel) and diflunisal (brand name Dolobid). Both work by mechanisms that stabilize the TTR tetramer. Like liver transplantation, the main issue with the TTR stabilizers is that they cannot prevent “seeding.” Nevertheless, TTR stabilizers are still used as the benefits outweigh the risks (Luigetti et al., 2020). Tafamidis is the more widely used TTR stabilizer and was approved by the FDA in 2019 for hATTR with cardiomyopathy. It can also be used off label in polyneuropathy. In the ATTR-ACT clinical trial, tafamidis was successful in reducing all-cause mortality and hospitalizations from cardiovascular complications and minimizing adverse events (Damy et al., 2021). Through this study, tafamidis got its approval and was considered a beneficial treatment option for cardiomyopathy (Hawkins et al., 2015). Diflunisal is also a TTR-stabilizing medication option for patients with hATTR, which belongs to the nonsteroidal anti-inflammatory drug class. Although not approved by the FDA for use in hATTR patients, it is used off label for polyneuropathy and cardiomyopathy. Diflunisal has been found to significantly reduce neuropathy progression and improve patient quality of life (Berk et al., 2013). Long-term use has been associated with characteristic nonsteroidal anti-inflammatory drug side effects like gastrointestinal bleeding, renal impairment, and cardiovascular stress (Luigetti et al., 2020).

Although the current treatment options for hATTR have had positive outcomes in patients, they do not target the genetic mutations specifically. Even after stabilizing the TTR tetramer, there is still overproduction of the mutant TTR protein. Both tafamidis and diflunisal are effective upon initiation, but they may not be able to sustain their effects for long-term use. For this reason, nucleic acid therapeutics have been developed. Nucleic acid therapeutics target the genomic basis of diseases and have longer-lasting effects regardless of the patient’s mutation type or disease stage at the initiation of therapy (Luigetti et al., 2020). For hATTR, four nucleic acid therapeutic agents have been developed, including two ASOs and two siRNAs. The goal of using these drugs in hATTR is to reduce the synthesis of the TTR protein by depleting the supply of the TTR mRNA (Hawkins et al., 2015).

e. Treatment of hereditary transthyretin amyloidosis with the antisense oligonucleotide drug inotersen; a potential ASO drug, eplontersen; and two small interfering RNA drugs, patisiran and vutrisiran

a. Epidemiology of hemophilia

Hemophilia is an inherited bleeding disorder primarily in men, with a prevalence rate between 12 and 15 cases in 100,000 individuals in the United States in recent years (Soucie et al., 2020). There are two types of hemophilia: hemophilia A and B. Approximately 80% of hemophilia cases are hemophilia A. Both types of hemophilia affect people from all racial and ethnic groups, with a slightly higher rate in European Americans (15.7/100,000) than African or Hispanic Americans (12.4/100,000) (Soucie et al., 2020). Roughly estimated hemophilia patients between 29,000 and 33,000 are living in the United States today, with the majority receiving comprehensive care in specialized clinical centers.

Although hemophilia occurs primarily in men, women may also have hemophilia. Almost 20% of patients with mild hemophilia are female, who also need care at specialized hemophilia treatment centers in the United States (Miller et al., 2021).

b. Symptoms of hemophilia

Hemophilia is a condition in which blood does not clot properly. Hemophilia can cause spontaneous bleeding and bleeding following medical procedures and physically endured traumas ​(Sahu et al., 2011). Internal bleeding inside the body is more of a concern with this condition than bleeding from small cuts, which are not as worrisome unless someone has an extreme case of hemophilia where they may also bleed easily for no apparent reason. A general symptom of hemophilia is excessive bleeding from cuts and medical procedures​. A person with hemophilia may experience nose bleeds more frequently and has a hard time controlling the bleeding and getting it to stop​. Hemophilia patients may develop hematomas from bleeding into the skin or muscle. Commonly seen is pain, swelling, and tightness in joints, specifically in the knees and elbows, due to bleeding in the joints​. Bleeding that is hard to control may be present during dental, mouth, and gums procedures (Shastry et al., 2014)​. In babies, there may be bleeding in the head following a difficult delivery, unnatural irritability without any apparent cause​, and uncontrolled bleeding after circumcision in male babies ​(Andersson et al., 2019). Hemophilia patients may also experience unusual bleeding following vaccinations, such as COVID-19 vaccination (Al Hennawi et al., 2022).

In severe cases of hemophilia, a bump on the head can cause bleeding in the brain (Zanon and Pasca, 2019). This is a rare but serious complication of the disease that can be characterized by the presence of seizures, vomiting, sleepiness, weakness, painful unrelenting headache, double vision, and weakness.

Diagnosing hemophilia typically occurs in early childhood, and the median age at diagnosis is 36 months for mild, 8 months for moderate, and 1 month for those with severe hemophilia (Kulkarni et al., 2009). More than half of people diagnosed with hemophilia A have the severe form. Seventy-five percent of infants who were diagnosed in the first month of life are related to a family history or whose mothers were known carriers ​(Kulkarni et al., 2009)​.

c. Genetic causes of hemophilia

Hemophilia is caused by an X-linked chromosomal mutation that causes a bleeding disorder due to the loss of the coagulation F-VIII in hemophilia A and coagulation F-IX in hemophilia B (Santagostino and Fasulo, 2013). Hemophilia is inherited as an X-linked recessive condition​. Severity of the disease is classified by the level of activity of coagulation factors in the blood (Santagostino and Fasulo, 2013)​. The lower the amount of coagulation factors present, the more severe the bleeding and the more severe disease a person has (Pavlova and Oldenburg, 2013). Typically, people have clotting factors forming a clot to stop bleeding. Still, in patients with hemophilia, the presence of clotting factors may be missing or present in very low levels​. Hemophilia can be inherited and is known as congenital hemophilia, characterized by the presence of low levels of a clotting factor caused by genetic mutations ​(Wang et al., 2017). People can also develop hemophilia with no family history of the condition, known as acquired hemophilia, where the person’s immune system attacks coagulation F-VIII or F-IX in the blood. Acquired hemophilia can be associated with multiple sclerosis, pregnancy, cancer, or drug reactions. Since hemophilia is an X-linked condition, it is found primarily in males as opposed to females since females have two X chromosomes and males have one X and one Y chromosome. For females to have hemophilia, they would need both X chromosomes from the mother and father for the disease to present itself. Males receive the X chromosome that contains the defective gene with hemophilia from the mother. Most females with the faulty gene for hemophilia on one X chromosome show no signs and symptoms of the condition but may have some unusual bleeding in some cases. A female who has one chromosome that contains the gene for the condition can pass it onto 50% of her children.

The molecular basis of hemophilia A and B is extremely diverse and caused by many different types of mutations, with single-nucleotide mutations, inversions, missense mutations, and deletions being found to cause both hemophilia A and B (Castaman and Matino, 2019)​. In hemophilia A, the shared genetic defect leading to this condition is intron 22 inversions, and in hemophilia B, a common congenital defect is missense mutations (Santagostino and Fasulo, 2013)​. Studies have shown that the type of mutation affecting either clotting F-VIII or F-IX is correlated with the plasma levels of these coagulation factors, meaning that more severe gene defects are associated with more severe cases of hemophilia (Castaman and Matino, 2019).

Many females who are carriers of the gene for hemophilia also have low factor expression, which can result in easy bruising, bleeding within joints, and heavy menstrual periods. The factor may be so low that some females who are carriers get diagnosed with hemophilia (Miller et al., 2021).

d. Current treatment options for hemophilia

There is no cure for both hemophilia A and B as it is a lifelong condition. However, current available treatments can improve quality of life by reducing the frequency and severity of bleeding episodes.

Current hemophilia treatments include replacement therapy that injects clotting factor(s) concentrates (Aledort et al., 2019). This includes a bypassing agent of either plasma-derived factor concentrates or recombinant factor concentrates. Plasma-derived concentrates come from human plasma filtered extensively to select the appropriate clotting factor needed for the patient. Recombinant factor concentrate comes from genetically engineered DNA technology. By injecting these concentrations of the clotting factors missing in the patient, it helps the blood clot properly for prophylactic and episodic care.

Due to its safety in preventing any blood-borne virus, a large portion of the hemophilia replacement therapy is the recombinant factor concentrates. Unlike plasma-derived concentrates, the recombinant F-VIII and F-IX do not contain any plasma or protein that could contribute to blood-borne viruses. Gene recombinant therapy offers the potential for a cure for patients with hemophilia by establishing continuous endogenous expression of F-VIII or F-IX following the transfer of a functional gene to replace the hemophilic patient's defective gene (Nathwani, 2019).

Treatment of hemophilia A would target those with congenital F-VIII deficiency. Instead of directly replacing the clotting factor, it can reduce the frequency of bleeding episodes. Hemlibra, also known as emicizumab, is a product prescribed for patients with hemophilia A (Lenting et al., 2017). Emicizumab is a macromolecule drug administered subcutaneously as it is an antibody consisting of two antigen-binding domains​. Antibodies can recognize both the enzyme F-IXa and the substrate F-X. By simultaneously binding enzyme and substrate, emicizumab mimics some part of the function exerted by the original cofactor, F-VIII, in that it promotes colocalization of the enzyme-substrate complex (Lenting et al., 2017)​. This leads to more thrombin molecules being generated, which can aid in stopping excessive bleeding. Emicizumab demonstrated statistically and clinically significant improvements in several types of bleeding outcomes such as treated bleeds, all bleeds, treated joint bleeds, and treated spontaneous bleeds (Oldenburg et al., 2017).

Patients with hemophilia B would be recommended with the congenital F-IX. BeneFix, also known as Nonacog alfa, is the recombinant F-IX used for the treatment of hemophilia B (LAMBERT et al., 2007).

The recombinant treatment has been efficacious. However, there have been ADRs reported with use. ADRs are frequent after F-VIII and can occur also with infusions after the first dose. Hence, recent use of F-VIII outside of hospital settings, such as home treatment, should be implemented with warning and caution (Batorova et al., 2022).

e. Treatment of hemophilia with the potential small interfering RNA drug fitusiran

Fitusiran, also known as ALN-AT3SC, is a siRNA therapeutic agent under development by Alnylam Pharmaceuticals in collaboration with Sanofi. Fitusiran is designed to target antithrombin (AT) mRNA to lower the production of AT protein in the liver and its levels in the blood, which can rebalance the imbalanced coagulation system caused by deficiencies in other clotting proteins, such as F-VIII (hemophilia A) or F-IX (hemophilia B), and promote hemostasis in hemophilia (Sehgal et al., 2015). Fitusiran is a synthetic double-stranded siRNA using the Alnylam GalNAc conjugate platform for hepatocyte-specific delivery. Its physiologically based pharmacokinetics and PD feature for silencing AT protein in the liver was proven in preclinical species of mice and monkeys (Sehgal et al., 2015; Ayyar et al., 2021). It is administered once monthly by subcutaneous injection in a dosage of 80 mg.

In clinical studies (Table 1), the PK, PD, and safety of fitusiran were first assessed in a phase 1 trial (NCT02035605) by Sanofi, completed in July 2017. The study enrolled 51 participants with healthy volunteers and patients with moderate or severe hemophilia A or B who did not have inhibitory alloantibodies (Pasi et al., 2017). Subcutaneous administration of fitusiran resulted in dose-dependent lowering of the AT protein levels on blood and increased thrombin generation in participants with hemophilia A or B. Fitusiran showed a desirable safety profile, with mild injection site reactions being the most common adverse events (Pasi et al., 2017). A further open-label phase 1 study using 17 male participants with moderate or severe hemophilia A or B with alloantibody inhibitors also concluded that fitusiran was generally well tolerated, could lower AT levels from baseline, and resulted in improved thrombin generation (Pasi et al., 2021).

Sanofi further conducted an open-label extended phase 1/2 study (NCT02554773) using 37 participants with hemophilia A or B with or without inhibitors to examine the longer-term durability, safety, and efficacy of fitusiran. The study concluded that fitusiran resulted in a lower annualized bleeding rate over a median of 2.6 years in patients with hemophilia A or B (Pipe et al., 2020).

Two multicenter, open-label, randomized phase 3 clinical trials have been completed by Sanofi. In the study of ATLAS-INH (NCT03417102), 60 patients with hemophilia A or B with inhibitors were recruited for assessing the efficacy and safety of fitusiran prophylaxis. The study concluded that subcutaneous fitusiran prophylaxis resulted in statistically significant reductions in annualized bleeding rates in participants with hemophilia A or B with inhibitors, with 66% of participants having zero bleeds in comparison with 5% in control (Young et al., 2023). The study ATLAS-A/B (NCT03417245), using 120 patients with hemophilia A or B without inhibitors, also concluded that fitusiran prophylaxis resulted in significant reductions in annualized bleeding rates compared with on-demand clotting factor concentrates and had no bleeding events in 51% of participants in comparison with 5% in control (Srivastava et al., 2023). The significant ADRs reported in these studies included abdominal pain, increased ALT and AST, cough, asthma, respiratory tract infection, nasopharyngitis, arthralgia, gastritis, and headache. Both phase 3 studies support that fitusiran has the potential to be transformative in the management of all people with hemophilia.

Two more phase 3 trials are nearly completed, but the results still need to be published. The ATLAS-PPX (NCT03549871) aims to determine the efficacy and safety of fitusiran prophylaxis in 80 severe hemophilia A or B patients previously receiving factors or bypassing agent prophylaxis. The study was completed in January 2022. Based on the press release by Sanofi, 63.1% of adults and adolescent patients treated with fitusiran experienced zero-treated bleeds in comparison with 16.9% of patients with prior factors or bypassing agent prophylaxis. The study met the primary endpoint and demonstrated that fitusiran prophylaxis significantly reduced bleeding episodes compared with primary factor or bypassing agent prophylaxis.

Another ongoing phase 3 study, ATLAS-PEDS (NCT03974113), aims to determine the efficacy and safety of fitusiran prophylaxis in male pediatric subjects aged 1 to less than 12 years with hemophilia. The study is estimated to be completed in August 2023. Sanofi's other ongoing phase 3 studies will determine the long-term safety and efficacy of fitusiran (ATLAS-OLE, NCT03754790) with a larger study cohort (355 participants) and test injection under the skin for preventing bleeding episodes (ATLAS-NEO, NCT05662319).

In conclusion, fitusiran has shown promising results in reducing bleeding episodes and improving quality of life in participants with hemophilia A and B. With further studies and trials, fitusiran would be approved by the FDA as a primary treatment option for hemophilia patients with better outcomes.

a. Epidemiology of atherosclerotic cardiovascular disease

ASCVD is prevalent and the leading cause of vascular diseases worldwide (Herrington et al., 2016). In the United States, the prevalence of ASCVD was 24 million, approximately 10% of the American adult (over the age of 21) population in 2019 (Gu et al., 2022). Lower socioeconomic non-White people have an elevated risk of ASCVD (Morris et al., 2018).

b. Symptoms of atherosclerotic cardiovascular disease

Atherosclerosis is a type of arteriosclerosis, which occurs when the arteries become thick and stiff, restricting blood flow from the heart to organs and tissues. Atherosclerosis is the buildup of plaque, which can include fats, cholesterol, and other substances in the arteries. This buildup narrows the arteries, preventing blood flow, and can lead to the development of several cardiovascular disorders such as coronary heart disease, peripheral arterial disease, and stroke.

c. Genetic causes of atherosclerotic cardiovascular disease

ASCVD is a complex disease with many contributing factors, including genetic variations. However, there is not one specific gene mutation that causes ASCVD. Rather, multiple genetic variants and environmental and lifestyle factors contribute to an individual's risk of developing ASCVD.

Many genes have been correlated with the development of ASCVD, including those involved in lipid metabolism, inflammation, and endothelial function (Nayor et al., 2021). These genes encode multiple proteins, including Apolipoprotein E (APOE), PCSK9, methylenetetrahydrofolate reductase (MTHFR), and tumor necrosis factor (TNF). Mutations in these genes have been associated with a higher risk of developing ASCVD. The APOE protein is involved in the transport of lipids, more specifically cholesterol (Mahley and Rall, 2000). The PCSK9 protein is involved in regulating LDL-C levels. Drugs typically target PCSK9 to lower LDL-C levels in high-risk patients (Lepor and Kereiakes, 2015). The MTHFR protein is involved in the metabolism of folate and homocysteine (Raghubeer and Matsha, 2021). The TNF protein is associated with the regulation of inflammation (Kalliolias and Ivashkiv, 2016). Variants of the genes encoding these proteins, alongside other risk factors such as diabetes and obesity, increase the risk of ASCVD (Nayor et al., 2021).

It is also important to note that these genetic factors alone are not solely responsible for the developmental risk of ASCVD. Environment and lifestyle factors also play a significant role in the development of ASCVD (Lechner et al., 2020).

In addition to genetic variations, elevated levels of Lp(a) have also been correlated with an increased risk for developing ASCVD (Reyes-Soffer et al., 2022). Lp(a) is a lipoprotein composed of an LDL-like particle attached to a glycoprotein. Lp(a) is often associated with the transport of cholesterol and other lipids, wound healing, and promotion of inflammation and plaque formation (Orsó and Schmitz, 2017). An elevated Lp(a) level is an independent signifier of ASCVD (Enas et al., 2019).

d. Current treatment options for atherosclerotic cardiovascular disease

Current treatment options for ASCVD focus on reducing the risk of developing cardiovascular events. These include many lifestyle changes, medications, and invasive procedures. These lifestyle changes include exercising regularly, cessation of smoking, weight management, and healthy eating, all of which are associated with a reduced risk of cardiovascular events. Current medications include statins, antiplatelet agents, angiotensin-converting enzyme (ACE) inhibitors, angiotensin receptor blockers (ARBs), and β blockers (Heidenreich et al., 2022). These medications aim to reduce the risk of cardiovascular events through many different pathways: statins lower cholesterol levels in the blood, antiplatelet agents aim to prevent blood clots, ACE inhibitors and ARBs lower blood pressure and prevent heart failure, and β blockers aim to reduce blood pressure and heart rate. In severe cases of ASCVD, invasive procedures such as angioplasty or coronary artery bypass surgery can be implemented to improve blood flow to the heart and further reduce the risk of cardiovascular events.

e. Treatment of atherosclerotic cardiovascular disease with the potential antisense oligonucleotide drug pelacarsen and the potential small interfering RNA drug olpasiran

Although lifestyle modifications and pharmacological interventions such as statins can help reduce the risk of ASCVD, new therapies still need to target the underlying mechanisms of the disease. One potential approach is to use RNA-based therapeutics, including ASO and siRNA drugs, to selectively target and inhibit the expression of proteins involved in lipid metabolism and inflammation. Two RNA agents that have shown promise in clinical trials are an ASO agent, pelacarsen, and a siRNA agent, olpasiran, both targeting elevated levels of Lp(a).

Pelacarsen, also termed Ionis-APO(a)-L_Rx, AKCEA-APO(a)-L_Rx, or TQJ230, is an ASO therapeutic agent under development by Ionis and Novartis for the treatment of ASCVD by targeting elevated Lp(a) levels (Karwatowska-Prokopczuk et al., 2021). Pelacarsen is a chemically modified ASO to enhance its stability, improve its pharmacokinetic properties, and reduce the risk of immune activation. The chemical structure of pelacarsen includes a backbone made of nucleotides, which are linked together by phosphodiester bonds. However, pelacarsen also contains several chemical modifications, including PS linkages, 2'-MOE modifications, and a cholesterol conjugate at the 3′ end of the molecule (Warden and Duell, 2022). These modifications enhance the drug's stability, improve its tissue distribution, and enhance its cellular uptake. Pelacarsen is administered once monthly by subcutaneous injection in a dosage of 120 mg.

As shown in Table 1, the safety, tolerability, PK, and PD of pelacarsen were determined by Ionis and Novartis in several phase 1 studies, including NCT02900027 (56 healthy volunteer participants with elevated triglycerides), NCT05337878 (29 healthy Japanese participants), and NCT05026996 (17 participants with mild hepatic impairment). These studies showed an overall improvement in the lipid profile with a favorable safety and tolerability profile (Alexander et al., 2019). A phase 2 study (NCT03070782) with a randomized, double blind, placebo-controlled, dose-ranging trial involving 286 patients with established ASCVD and elevated Lp(a) levels was further conducted and completed in November 2018. The study also showed that pelacarsen reduced Lp(a) levels in a dose-dependent manner in patients with ASCVD disease (Tsimikas et al., 2020) and also had neutral to mild lowering of LDL-C levels (Yeang et al., 2022). A phase 3 study Lp(a) HORIZON (NCT04023552) is under intervention with an actual enrollment of 8323 participants to assess the impact of Lp(a) lowering with pelacarsen on major cardiovascular events in patients with ASCVD (Plakogiannis et al., 2021). The study is expected to be completed in May 2025. No approved pharmacological therapies are currently available to lower Lp(a) effectively. Lp(a) HORIZON study may provide a solution for 8 million patients with ASCVD disease.

Olpasiran, also known as AMG 890, is a siRNA therapeutic agent under development by Amgen to treat ASCVD by inhibiting translation of the Lp(a) protein in hepatocytes, leading to a marked reduction in Lp(a) levels in the circulation (O’Donoghue et al., 2022a). Olpasiran is also chemically modified to enhance its stability, improve its pharmacokinetic properties, and reduce the risk of immune activation. These modifications include PS linkages to strengthen stability, 2'-MOE modifications to enhance its affinity to the target sequence, and a GalNAc conjugation to increase its uptake in the liver. Olpasiran is administered once monthly by subcutaneous injection in a dosage of 75 mg.

The PK, PD, and tolerability of olpasiran were studied by Amgen in several populations, including NCT04987320 (24 Chinese participants with elevated serum Lp(a) levels), NCT05481411 (25 participants with various degrees of hepatic impairment), NCT05489614 (32 participants with normal and multiple degrees of renal impairment), and 27 healthy Japanese and non-Japanese participants (Sohn et al., 2022). These studies found that olpasiran was well tolerated with no clinically significant adverse events or laboratory abnormalities.

Supported by the phase 1 studies on safety and tolerability, a phase 2 clinical trial (NCT04270760) with a double blind, randomized, placebo-controlled study was conducted and completed in November 2022 by Amgen to evaluate the efficacy, safety, and tolerability of olpasiran in 290 participants with elevated Lp(a) levels. The study concluded that olpasiran therapy significantly reduced Lp(a) concentrations from 70% to 100% in a dose-dependent manner in patients with established ASCVD disease (O’Donoghue et al., 2022b). A multicenter phase 3 trial OCEAN(a) (NCT05581303) is under intervention with an estimated enrollment of 6000 participants to assess the impact of olpasiran on major cardiovascular events in patients with ASCVD disease and elevated Lp(a) levels. The study is estimated to be completed in December 2026. Olpasiran has shown to be a promising treatment approach that produces a profound and sustained reduction in Lp(a) concentrations in the circulation in clinical trials.

Both ASO and siRNA drugs under development have shown great promise and may provide a solution for millions of patients worldwide with ASCVD disease.

a. Epidemiology of α-1 antitrypsin deficiency-associated liver disease

AATLD is not a rare disease but a disease rarely diagnosed, with approximately 180,000 individuals worldwide (de Serres, 2003). AATLD is extremely under-reported in the United States, with fewer than 10,000 individuals diagnosed, but an estimated prevalence may be over 100,000 cases (30 per 100,000) (Stoller and Brantly, 2013; Ashenhurst et al., 2022). A long delay may happen between initial symptoms and first detection, and the need to see multiple physicians may also be required before diagnosis (Stoller and Brantly, 2013).

b. Symptoms of α-1 antitrypsin deficiency-associated liver disease

AATLD affects many different areas of the body, the most prominent being the liver. However, the disease has also been known to affect the lungs as well (Teckman and Mangalat, 2015). AATLD is caused by the synthesis of an atypical and mutated α-1 antitrypsin protein (AAT). The misfolded protein forms polymers that prevents it from leaving the hepatocytes and accumulating in the liver (Silverman et al., 2013). This, in turn, leads to unwanted cellular consequences, such as endoplasmic reticulum stress, hepatocellular injury, inflammation, and apoptosis. Over time, these effects can result in liver diseases, ranging from mild asymptomatic enzyme elevations to hepatic fibrosis, cirrhosis, and hepatocellular carcinoma (Teckman and Mangalat, 2015). Individuals may also develop lung diseases like emphysema or chronic obstructive pulmonary disease (Anzueto, 2015). Symptoms affecting the lungs include dyspnea, cough, and wheezing. Many individuals with AATLD develop serious conditions like asthma, emphysema, or chronic bronchitis (Tejwani and Stoller, 2021). Liver dysfunction is a major indicator of AATLD, especially in children (Lin et al., 2019). Over 50% of the children with AATLD have liver dysfunction. When under 18, individuals with AATLD face cirrhosis and other life-threatening disorders about 5% of the time (Nelson et al., 2012). Symptoms have also been displayed in neonatal children. A significant symptom seen in infants shortly after birth is cholestatic jaundice and hepatitis (Nelson et al., 2012).

c. Genetic causes of α-1 antitrypsin deficiency-associated liver disease

AATLD is caused by mutations in the serine protease inhibitor 1 (SERPINA1) gene encoding the AAT protein. More than 200 mutations have been identified in the SERPINA1 gene in various populations (Foil, 2021). Approximately 40% of these mutations are thought to cause some forms of AATLD (Seixas and Marques, 2021). Due to the sheer number of mutations that cause AATLD, it affects individuals very differently. Individuals with AATLD who experience liver diseases are commonly seen with a homozygous Z allele (Bouchecareilh, 2020). These individuals are noted as PiZZ homozygous. The PiZZ genotype is frequently referred to as the most severe form of AATLD as it results in severe clinical presentations (Santos and Turner, 2020). That being said, other genotypes, like PiSZ and PiMZ, can also present severe conditions (Santos and Turner, 2020).

d. Current treatment options for α-1 antitrypsin deficiency-associated liver disease

Currently, there are no pharmacological therapies that can cure AATLD. However, numerous options can be used to manage the disease and its corresponding effects. There are also promising pharmacological interventions being developed to cure AATLD. Despite these efforts, the primary course of action involves treating the symptoms of AATLD. As mentioned above, these symptoms can take many forms, which results in a high variability in the ways AATLD can be treated.

A major method of treating AATLD is to manage it. This is primarily done alongside a physician monitoring the effects and complications of chronic liver diseases, which may arise from having AATLD (Teckman, 2013). Prescribers treating the complications of chronic liver diseases include everything from bleeding to hepatocellular carcinoma. These symptoms are usually managed by physicians who meet regularly with the patient to ensure that there are no other complications related to AATLD (Teckman, 2013). By doing this, less severe cases can be managed, often resulting in healthy lives for the patients.

In severe cases, liver transplantation must be performed. This is usually only performed when cirrhosis or hepatocellular carcinoma is present (Carey et al., 2013). Liver transplantation is the only way to truly cure AATLD (Zamora and Ataya, 2021).

AAT augmentation therapy is a replacement therapy for treating patients with AATLD who have emphysema (Barjaktarevic and Miravitlles, 2021). This therapy uses normal AAT protein derived from the blood of healthy donors to increase the amount of AAT in the lungs of patients with AAT deficiency. AAT augmentation treatment has been shown to slow the progression of emphysema and lung destruction when caused by AATLD (Edgar et al., 2017). Despite this, AAT augmentation is simply a way to subdue the symptoms of AATLD in the lung. To be clear, AAT augmentation treatment does not subdue AATLD’s effects on the liver but only helps to treat AATLD’s effects in the lungs.

e. Treatment of α-1 antitrypsin deficiency-associated liver disease with the potential small interfering RNA drugs fazirsiran and belcesiran

siRNA therapeutic strategy has been applied to reduce the production of mutated AAT proteins in the livers of AATLD patients. Two siRNA drugs, fazirsiran and belcesiran, are in the development stages.

Fazirsiran, also known as ARO-AAT, is a siRNA therapeutic agent currently being developed by Arrowhead and Takeda to treat AATLD. Fazirsiran is an investigational siRNA agent containing a synthetic, double-stranded siRNA duplex conjugated to GalNAc to facilitate endosomal uptake and intracellular delivery in hepatocytes (Wooddell et al., 2020). Fazirsiran has been shown to reduce hepatic Z-AAT polymer, restore endoplasmic reticulum and mitochondrial health, normalize expression of disease-associated genes, reduce inflammation, and prevent tumor formation in the PiZ transgenic mouse model (Wooddell et al., 2020). Fazirsiran also provided robust and persistent knockdown of ATT levels in PiZZ patients (Turner et al., 2018). It is administered once monthly by subcutaneous injection in a dosage of 100 mg.

As shown in Table 1, the safety, tolerability, pharmacokinetics, and pharmacodynamics of fazirsiran were determined in a phase 1 study (AROAAT-1001, NCT03362242) with 45 participants, completed in October 2018, which provided a strong base of the safety profile to support two ongoing phase 2 studies, AROAAT-2002 (NCT03946449) and SEQUOIA (NCT03945292).

For AROAAT-2002 (NCT03946449), with a start date in December 2019 and an estimated completion in August 2024, the clinical trial had 16 participants split up into three cohorts. Every cohort received doses of fazirsiran subcutaneously on day 1 and week 4 followed by every 12 weeks dosing. However, the different cohorts had different endpoints. For example, cohort 1, consisting of four individuals, received a 200-mg dose of fazirsiran until week 24. Cohort 1b, consisting of four individuals, also had an endpoint of week 24 but only received 100-mg subcutaneous injections. Cohort 2, composed of eight individuals, received 200-mg subcutaneous injections and had an endpoint of week 48. The goal of this clinical trial was to measure the baseline change in mutant protein (Z-AAT) concentrations. The study results showed that all patients had reduced levels of Z-AAT protein in the liver at the end of the trial (Strnad et al., 2022). Another important finding of the study is that there were no adverse side effects in any individual.

For SEQUOIA (NCT03945292), with a start date in August 2019 and completion in November 2021, the clinical trial consisted of 40 individuals diagnosed with AATLD (Remih et al., 2021). Patients with baseline fibrosis received one of three doses (25, 100, or 200 mg) of fazirsiran subcutaneously. The goal of this study was also to determine critical aspects including safety, efficacy, and tolerability of fazirsiran. All three of these cohorts showed dramatic decreases in the mutant AAT protein, with the largest reduction being 94% with a dose of 200 mg (Remih et al., 2021). Another interesting point is that 50% of the individuals saw improvements in their lung fibrosis.

Since the findings of both phase 2 clinical trials saw effective reductions in the mutant Z-AAT protein, fazirsiran can play a significant role in treating AATLD. This statement is further compounded by the fact that neither trial saw individuals with significant adverse side effects. A randomized, double blind, placebo-controlled phase 3 study has been started since March 2023, with an estimated enrollment of 160 participants, to further evaluate the efficacy and safety of fazirsiran in the treatment of AATLD (NCT05677971). The study is estimated to be completed in March 2027. Fazirsiran has the potential to provide life-changing treatment to people suffering from AATLD.

Belcesiran, also known as DCR-A1AT, is another siRNA therapeutic agent under development by Dicerna Pharmaceuticals to treat AATLD. Belcesiran contains 22 bases of ribonucleotides on the guide strand (antisense) targeting the SERPINA1 mRNA and 36 bases on the passenger strand (sense) with tetraloop hairpin. The sequence is conjugated with 4 GalNAc molecules using GalXC RNAi technology invented by Dicerna scientists (Kumar and Turnbull, 2023). Multivalent GalNAc moieties are linked to siRNA at the region of the tetraloop hairpin (Hu et al., 2020a), which introduces a stable complementary structure in the siRNA sense strand. This design erases sense strand–mediated off-target effects and increases the stability and specificity of siRNAs targeting their mRNA targets. This allows GalXC RNA technology to have many benefits, from high specificity to hepatocytes and increased duration of action to a straightforward dosing process. Belcesiran is subcutaneously delivered while still providing specificity to liver cells, particularly hepatocytes.

After proving the concept and defining the pharmacokinetic features of belcesiran in preclinical studies, a phase 1 clinical trial was initiated in October 2019 and completed in July 2021 (NCT04174118) (Remih et al., 2021). A phase 2 clinical trial was undertaken in February 2021 and is estimated to be completed in September 2023 (NCT04764448).

For the phase 1 clinical trial, two treatment arms were used. One cohort received belcesiran subcutaneously. The other cohort received a placebo containing 0.9% NaCl saline, also subcutaneously. The goals of the phase 1 clinical trial were to identify the incidence of adverse effects, significant physical examination findings, and changes in 12-lead ECGs, all over the span of 2 months. Changes in AAT protein concentrations were also tested. These measurements were taken at varying time frames, from 3 days to up to 57 days. Unfortunately, due to its recent development, the final data of the phase 1 clinical trial have not been posted. However, interim data from phase 1 showed no serious adverse side effects with belcesiran.

For the phase 2 clinical trial, three cohorts were used, each with their own placebo and belcesiran treatment arms. Cohorts were differentiated based on the length of treatment with belcesiran or placebo. Cohort 1 received belcesiran/placebo injections for 24 weeks. Cohorts 2 and 3 received the same injections for 48 and 96 weeks, respectively. This trial aims to evaluate belcesiran’s effects on adult patients with PiZZ AATLD. Criteria like safety, tolerability, and pharmacokinetics are measured. This is being done through a variety of measurements taken through 12-lead ECGs, physical examinations, vital sign measurements, and clinical laboratory tests. The efficacy of belcesiran on the treatment of AATLD will be released after the clinical trial is completed.

As there is no cure for AATLD, belcesiran provides hope for patients suffering from chronic symptoms. Although its phase 1 and phase 2 clinical trials data are not published, the GalXC siRNA technology provides hope for patients struggling with AATLD.

AATLD is an extremely dangerous and often misunderstood disease. With its effects having a wide range of presentations, it is often underdiagnosed. Even if it is diagnosed, there is no pharmacological cure to treat AATLD. The only way to treat AATLD is to manage the side effects or undergo extreme interventions like liver transplantation. However, the future is bright for individuals suffering with AATLD as belcesiran and fazirsiran have shown promising results (Remih et al., 2021). Fazirsiran has already demonstrated effectiveness in its two phase 2 clinical trials. With a phase 3 clinical trial being initiated, fazirsiran shows promise. Despite belcesiran having little results, its GalXC technology shows tremendous upside in its ability to deliver the drug to hepatocytes effectively. siRNA therapeutics have clearly made dramatic jumps recently and provide promising hope to people suffering from chronic diseases like AATLD.

a. Epidemiology of the complement-mediated diseases

The complement system is the critical part of the innate immune system that defends our body from microbial infections and clears injured cells (Noris and Remuzzi, 2013). In normal conditions, the complement system is tightly controlled and regulated to avoid attack on autologous tissues. The complement system consists of nine central components (C1 to C9). When some components are hyperactivated, they may drive a severe inflammatory response in numerous organs and may result in various CMD. For example, hyperactivation of C5 is associated with the CMD of PNH (Kulasekararaj et al., 2022), aHUS (Tanaka et al., 2021), and IgAN (Rizk et al., 2019).

PNH is a rare chronic hematologic disease associated with inappropriate complement activity on blood cells, resulting in intravascular hemolysis, thromboembolic events, and organ damage (Kulasekararaj et al., 2022). The prevalence of PNH in the United States is estimated to be 1.2 to 1.3 cases per 100,000 people, which is similar across sex and increases with age (Jalbert et al., 2019).

aHUS is a rare genetic disease that causes tiny blood clots to form in blood vessels, blocking blood flow to essential organs and causing kidney failure, heart disease, and other serious health problems. The prevalence rate of aHUS is less than 1 per 100,000 individuals worldwide (Yan et al., 2020).

IgAN is the most common glomerulonephritis worldwide, with an incidence rate of approximately 2.5 per 100,000 in the last two decades (Rodrigues et al., 2017; Storrar et al., 2022), but has significant geographical variations, with a higher prevalence rate in East Asia, then in Europe and Africa (Magistroni et al., 2015).

b. Symptoms of the complement-mediated diseases

Symptoms of PNH include blood clots, weakness, fatigue, headache, abdominal pain, back pain, dark urine, easy bleeding, and shortness of breath. The symptoms of aHUS may include paleness, swelling, fatigue, nausea, vomiting, drowsiness, and hypertension. The most common symptoms of IgAN are visible blood in urine (hematuria), proteinuria, hypertension, flank pain, and ankle swelling (edema).

c. Genetic causes of the complement-mediated diseases

A somatic mutation in the phosphatidylinositol glycan anchor biosynthesis class A gene has been associated with deficiency of the glycosylphosphatidylinositol anchor, leading to complement-mediated hemolysis in PNH patients (Takeda et al., 1993). The genetic mutations in the complement factor H (CFH) gene have been considered as the most common cause of inherited aHUS (Wong and Kavanagh, 2018). Mutations in other complement factor genes, including C1, C3, and CHB, are also associated with aHUS. Due to the striking phenotypic variations, the genetic basis of IgAN is still unclear (Feehally and Barratt, 2015).

d. Treatment options of the complement-mediated diseases

To manage the symptoms and reduce potential damage to the kidneys, several classes of medications are normally the options for the treatment of CMD. Antihypertensive drugs, such as ACE inhibitors and ARBs, are normally prescribed to lower blood pressure to prevent or delay further kidney damage for CMD patients (Dillon, 2004). Lipid-lowering medicines are also used to control cholesterol levels and slow down kidney damage in CMD patients with high cholesterol levels (Moriyama et al., 2014). Diuretics can be applied to control swelling and edema (Uzu et al., 2005).

To target the hyperactivated complement component proteins, the FDA has approved monoclonal antibody and peptide drugs to treat CMD diseases. The liver is the major organ producing the majority of the complement proteins, and Kupffer cells in the liver are the important immune cells (Thorgersen et al., 2019). A pivotal part of liver homeostasis is to control the complement system in immune responses. Blocking the production of the key complement component proteins in the liver provides a strategy to treat CMD due to hyperactivation of the complement component proteins. Eculizumab and ravulizumab are humanized monoclonal antibodies against C5, approved by the FDA for the treatment of PNH and aHUS (Dmytrijuk et al., 2008; McKeage, 2019). The genetic variants in the C5 gene are associated with response to eculizumab (Nishimura et al., 2014). Pegcetacoplan, a PEGylated pentadecapeptide binding to C3 protein, is also approved by the FDA to treat PNH patients (Hoy, 2021).

Recently, a newly developed humanized monoclonal antibody named pozelimab has shown full inhibition function against C5 activity in mice (Latuszek et al., 2020) and nonhuman primates (Devalaraja-Narashimha et al., 2022). Developed by Regeneron Pharmaceuticals, pozelimab is under a series of clinical trials to evaluate its efficacy and safety in treating the CMD diseases.

In addition to using antibodies against C5, siRNA has also been considered as another approach to block C5 production in hepatocytes for treating CMD diseases.

e. Treatment of the complement-mediated diseases with the potential small interfering RNA drug cemdisiran

Cemdisiran, under development by Alnylam Pharmaceuticals, is a siRNA agent with chemically modified double-stranded RNA sequences, in which the sense strand contains 21 nucleotides, and the antisense strand contains 25 nucleotides (Badri et al., 2021). A tri-antennary GalNAc is conjugated to the 3′-end of the sense strand for hepatocyte-specific delivery. Through endocytosis into the hepatocytes, cemdisiran specifically targets C5 mRNA, resulting in decreased hepatic synthesis and lower circulating levels of C5 protein. Thus, cemdisiran is expected to ameliorate the signs and symptoms of CMD, offering a novel approach for treating the CMD diseases. Cemdisiran is administered once weekly by subcutaneous injection in a dosage of 200 mg.

The PK, PD, safety, and tolerability of cemdisiran were first assessed by a single- and multiple-ascending dose phase 1/2 study (NCT02352493) with 32 healthy adult volunteers and 30 PNH patients. A long PD duration of action in the liver for robust C5 suppression was found in the study, with acceptable safety profiles (Badri et al., 2021). The PD and safety results support further evaluation of cemdisiran in CMD as either monotherapy or in combination with a C5 inhibitor antibody. Two open-label phase 1 studies (NCT04601844 and NCT04940364) conducted by Regeneron Pharmaceuticals further evaluated the PK, PD, safety, and tolerability of cemdisiran in combination with pozelimab in healthy adult volunteers, supporting a potential long-acting treatment of PNH and other CMD diseases.

Alnylam has conducted a phase 2 study (NCT03841448) together with Regeneron to evaluate the efficacy of cemdisiran in adults with IgAN. The treatment with cemdisiran resulted in a 37% percent mean reduction of C5 protein from baseline in the urine relative to placebo, showing the expected efficacy with IgAN patients. The overall safety and tolerability profile of cemdisiran in the phase 2 study supports continued clinical development. Alnylam is also conducting a phase 2 study, DANCE (NCT03999840), in patients with aHUS to switch from eculizumab to cemdisiran.

Currently, Regeneron is performing a phase 2 study (NCT04888507) to examine cemdisiran and pozelimab combination therapy in adult patients with PNH who switch from eculizumab therapy and a phase 2 study (NCT04811716) with PNH who have received pozelimab monotherapy. These phase 2 studies are nearly completed. Although their results have not been published, cemdisiran may become another therapeutic option besides monoclonal antibodies to suppress C5 production in the liver to treat various CMD diseases.

Three phase 3 studies are currently in the stages of participant recruitment. The ACCESS-EXT (NCT05744921) study will examine the long-term safety, tolerability, and effectiveness of pozelimab and cemdisiran combination therapy in patients with PNH. The ACCESS-1 (NCT05133531) study will evaluate the efficacy and safety of pozelimab and cemdisiran combination therapy in patients with PNH who are complement inhibitor treatment-naïve or have not received complement inhibitor therapy. The NIMBLE (NCT05070858) study will determine the efficacy and safety of pozelimab and cemdisiran combination therapy in patients with symptomatic generalized myasthenia gravis.

In conclusion, by directly targeting C5 mRNA in hepatocyte cells, the siRNA drug cemdisiran, under development by Alnylam, has shown promising efficacy to robustly suppress production of C5 protein and elevated levels in the circulatory system with favorable safety profiles. The combination therapy of cemdisiran with the C5 monoclonal antibody pozelimab may provide a therapeutic solution for managing various CMD diseases, including PNH, aHUS, and IgAN.