Pathogenicity assessment of genetic variants identified in patients with severe hypertriglyceridemia: Novel cases of familial chylomicronemia syndrome from the Dyslipidemia Registry of the Spanish Atherosclerosis Society.

Objective: Genetic testing is required to confirm a diagnosis of familial chylomicronemia syndrome (FCS). We assessed the pathogenicity of variants identified in the FCS canonical genes to diagnose FCS cases.

Methods: 245 patients with severe hypertriglyceridemia underwent next-generation sequencing. Preliminary variant pathogenicity criteria and classification, based on the American College of Medical Genetics and Genomics guidelines, were obtained online and verified. Phenotype evaluation was based on lipoprotein lipase activity deficiency, a clinical score, and/or type I hyperlipoproteinemia determined in 25 patients.

Results: Twenty-four biallelic variants were analyzed. Evidence-based criteria allowed the reclassification of 8 likely pathogenic (LP) variants in the LPL, APOA5, and LMF1 genes into pathogenic (P) and the change of 2 variants of uncertain significance (VUS) to LP. Conversely, 2 variations in LMF1 remained as VUS. Additionally, 1 variant in LPL and 2 in GPIHBP1 were likely benign. Twenty FCS cases had biallelic P/LP variants and 1 patient, with an FCS phenotype, harbored biallelic VUS. FCS was excluded from 4 patients with pathogenic/likely benign combinations.

Conclusions: The analysis of the clinical and biochemical features of patients with variants in the FCS canonical genes allowed a confident variant classification that helped in the diagnosis of novel FCS cases.