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Familial chylomicronemia syndrome (FCS) is a rare autosomal recessive condition. Effective treatment is important as patients are at risk for severe and potentially fatal acute pancreatitis. We review recent developments in pharmacologic treatment for FCS, namely biological inhibitors of apolipoprotein (apo) C-III and angiopoietin-like protein 3 (ANGPTL3). FCS follows a biallelic inheritance pattern in which an individual inherits two pathogenic loss-of-function alleles of one of the five causal genes – LPL (in 60–80% of patients), GPIHBP1, APOA5, APOC2, and LMF1 – leading to the absence of lipolytic activity. Patients present from childhood with severely elevated triglyceride (TG) levels >10 mmol/L. Most patients with severe hypertriglyceridemia do not have FCS. A strict low-fat diet is the current first-line treatment, and existing lipid-lowering therapies are minimally effective in FCS. Apo C-III inhibitors are emerging TG-lowering therapies shown to be efficacious and safe in clinical trials. ANGPTL3 inhibitors, another class of emerging TG-lowering therapies, have been found to require at least partial lipoprotein lipase activity to lower plasma TG in clinical trials. ANGPTL3 inhibitors reduce plasma TG in patients with multifactorial chylomicronemia but not in patients with FCS who completely lack lipoprotein lipase activity. Apo C-III inhibitors currently in development are promising treatments for FCS. [ABSTRACT FROM AUTHOR]

Context: Patients with rare familial chylomicronemia syndrome (FCS) and relatively common multifactorial chylomicronemia syndrome (MCS) both express severe hypertriglyceridemia, defined as plasma triglyceride concentration ≥10 mmol/L (≥885 mg/dL). Clinically there can be confusion between the two conditions., Objective: To compare clinical and biochemical phenotypes in patients with genotypically characterized FCS and MCS., Methods: We performed targeted sequencing of DNA from 193 patients with severe hypertriglyceridemia, classified them as having either FCS or MCS and compared clinical and biochemical characteristics., Results: FCS compared to MCS patients were significantly younger (31.4 ± 16.7 vs. 51.0 ± 11.3 years; P =0.003), with earlier age at symptom onset (15.0 ± 15.8 vs. 37.8 ± 8.8 years; P =0.00066), lower body mass index (23.3 ± 3.1 vs. 30.7 ± 5.0 kg/m2; P =0.000016), and higher prevalence of pancreatitis events (81.8% vs. 35.2%; P=0.003). Furthermore, FCS compared to MCS patients had a higher ratio of triglyceride to total cholesterol, i.e. 4.18 ± 0.92 vs 1.08 ± 0.51 (P <0.0001) and lower plasma apolipoprotein B, i.e. 0.56 ± 0.15 vs 1.02 ± 0.43 g/L (P <0.0001). MCS patients with heterozygous pathogenic variants had a relatively more severe clinical presentation than other MCS genetic subgroups., Conclusions: FCS patients have notable phenotypic differences from MCS patients, although there is overlap. While genetic analysis of patients with persistent severe hypertriglyceridemia can definitively diagnose FCS, 8.2% of MCS patients with sustained refractory hypertriglyceridemia behave functionally as if they have FCS, which should influence their eligibility for novel therapies for severe hypertriglyceridemia., (© The Author(s) 2024. Published by Oxford University Press on behalf of the Endocrine Society.)