Published May 7, 2025
By Anthony M. Calabro, MA

Familial chylomicronemia syndrome (FCS) is a rare autosomal recessive lipid disorder characterized by the accumulation of chylomicrons in plasma, resulting in extreme hypertriglyceridemia (HTG), often with triglyceride (TG) levels exceeding 1000 mg/dL. This accumulation leads to an increased risk of recurrent acute pancreatitis, eruptive xanthomas, lipemia retinalis, and hepatosplenomegaly. In the past 5 years, research has advanced in the areas of diagnosis, pathophysiology, and therapeutics, culminating in new FDA-approved treatments for this debilitating disorder.^1-3

FCS is caused by biallelic pathogenic variants in genes critical to lipolysis, most commonly lipoprotein lipase (LPL), but also APOC2, APOA5, LMF1, and GPIHBP1. These genetic mutations lead to near-complete or complete absence of functional LPL activity, preventing the hydrolysis of triglycerides from chylomicrons. As a result, triglyceride-rich lipoproteins persist in the plasma, producing severe HTG and related complications. The estimated global prevalence is approximately 1 in 1 million individuals, though underdiagnosis may affect these figures significantly.^1,2

The early identification of FCS is vital to preventing pancreatitis and other complications. Diagnostic criteria include persistent fasting triglyceride levels ≥ 880 mg/dL, clinical features such as recurrent pancreatitis and eruptive xanthomas, and laboratory findings such as the presence of chylomicrons after a 12-hour fast and low apolipoprotein B levels.¹

Importantly, FCS must be differentiated from multifactorial chylomicronemia syndrome (MCS), which is more common and results from polygenic and secondary causes like uncontrolled diabetes, obesity, or alcohol intake. Unlike FCS, MCS often responds to traditional triglyceride-lowering agents. For FCS, the gold standards for diagnosis is genetic testing that confirms biallelic mutations in one of the causative genes.^1,3

Generally, the key to FCS management is a  low-fat diet with avoidance of alcohol and simple sugars. While this dietary regimen can mitigate TG elevation, adherence is difficult and monotherapy often fails to achieve target TG levels or prevent pancreatitis.¹

A major therapeutic milestone occurred in December 2024, when the FDA approved olezarsen, an antisense oligonucleotide targeting APOC3 mRNA. By reducing apoC-III levels—a key inhibitor of LPL—olezarsen enhances remnant clearance and decreases plasma TG. Phase 3 trials demonstrated a median TG reduction of 44% from baseline, along with a reduction in pancreatitis episodes.^4,5

Another promising agent under FDA review is plozasiran, a small interfering RNA (siRNA) therapy also targeting APOC3. In the PALISADE phase 3 study, plozasiran produced significant and durable reductions in TG levels and lowered the frequency of pancreatitis attacks in patients with FCS.^7,8

Volanesorsen, also targeting APOC3, was approved in Europe in 2019. Though effective in reducing TG levels by more than 70% in clinical trials,⁹ its use has been limited by adverse effects such as thrombocytopenia, requiring regular platelet monitoring.^3,6  Additionally, ARO-APOC3 is a novel RNA interference (RNAi) agent targeting APOC3 mRNA in hepatocytes that is currently in early-phase clinical trials. Preliminary data suggest robust TG-lowering effects with potentially fewer systemic side effects than volanesorsen.¹⁰

Conventional TG-lowering medications such as fibrates, statins, and omega-3 fatty acids are largely ineffective in FCS due to the fundamental absence of LPL activity. This distinction further highlights the necessity of precision therapies targeting upstream regulators of triglyceride metabolism, such as apoC-III.^1,11

Optimal management of FCS requires a team-based approach, involving:

• Endocrinologists and lipidologists to lead  pharmacologic management and monitor lipid panels.

• Registered dietitians to support patients in maintaining a strict low-fat diet.

• Gastroenterologists to manage complications, particularly recurrent acute pancreatitis.

• Genetic counselors to facilitate family testing and help patients understand the inheritance pattern.

Furthermore, engaging mental health professionals can help patients cope with the psychological burden of strict dietary restrictions and chronic disease. Patient education is central to long-term adherence and quality of life. Support networks and digital tools (e.g., meal planning apps, telehealth dietician check-ins) can improve compliance and outcomes as well.

FCS is a rare but serious genetic lipid disorder marked by severe hypertriglyceridemia and high risk of pancreatitis. While dietary restriction remains foundational, the approval of olezarsen and ongoing development of agents like plozasiran and ARO-APOC3 have transformed the therapeutic landscape in the last 5 years.

1. Javed F, Hegele RA, Garg A, et al. Familial chylomicronemia syndrome: An expert clinical review from the National Lipid Association. J Clin Lipidol. Published online March 22, 2025. doi:10.1016/j.jacl.2025.03.013

2. Endocrine Society. Familial chylomicronemia syndrome. Published 2023. Accessed April 20, 2025. https://www.endocrine.org/patient-engagement/endocrine-library/familial-chylomicronemia-syndrome

3. Gallo A, Donato LJ, Sparks JD. Familial chylomicronemia cyndrome: current perspectives and management strategies. Curr Atheroscler Rep. 2020;22(11):63. doi:10.1007/s11883-020-00872-7.

4. Izar MC, Fonseca FAH. Novel therapeutics for familial chylomicronemia syndrome. Curr Atheroscler Rep. 2025;27(4):51. doi:10.1007/s11883-025-01050-z.

5. Reuters. US FDA approves Ionis Pharma's genetic disorder drug. Reuters website. Published December 19, 2024. Accessed April 20, 2025. https://www.reuters.com/business/healthcare-pharmaceuticals/us-fda-approves-ionis-pharmas-genetic-disorder-drug-2024-12-19

6. Volanesorsen for the treatment of familial chylomicronemia syndrome. Drugs. 2020;80(5):491-499. doi:10.1007/s40265-020-01251-0.

7. Plozasiran under review for familial chylomicronemia syndrome. Endocrinology Advisor. Published January 23, 2025. Accessed April 20, 2025. https://www.endocrinologyadvisor.com/news/plozasiran-under-review-for-familial-chylomicronemia-syndrome/

8. Watts GF, Rosenson RS, Hegele RA. Plozasiran for Managing Persistent Chylomicronemia and Pancreatitis Risk. New England Journal of Medicine. Published online September 2, 2024. doi:10.1056/NEJMoa2409368

9. Witztum JL, Gaudet D, Freedman SD, et al. Volanesorsen and triglyceride levels in familial chylomicronemia syndrome. N Engl J Med. 2019;381(6):531-542. doi:10.1056/NEJMoa1715944

10. Gaudet D, Pall D, Watts GF, et al. Plozasiran (ARO-APOC3) for Severe hypertriglyceridemia: The SHASTA-2 randomized clinical trial. JAMA Cardiol. 2024;9(7):620-630. doi:10.1001/jamacardio.2024.0959

11. Kastelein JJP, Stroes ESG. FCS treatment: unmet needs and evolving options. Curr Opin Lipidol. 2023;34(2):79-84. doi:10.1097/MOL.0000000000000821.