Tang_2026_Front.Physiol_17_1820368

BACKGROUND: Lipoprotein lipase (LPL) is essential for plasma triglyceride (TG) hydrolysis, and biallelic LPL loss-of-function variants cause familial chylomicronemia syndrome. However, the clinical and functional significance of heterozygous LPL variants remains incompletely characterized. We investigated two heterozygous LPL missense variants, c.1187A>T (p.Glu396Val) and the novel c.1251G>C (p.Trp417Cys), in patients with severe hypertriglyceridemia (HTG). METHODS: Two probands underwent comprehensive clinical, biochemical, and imaging assessments. Genetic analysis involved whole-exome sequencing and Sanger confirmation. Variant interpretation incorporated in silico prediction, evolutionary conservation, AlphaFold-based residue mapping, LPL-GPIHBP1 structural-context analysis, and NetCGlyc prediction. Functional effects were assessed in HEK293T cells transfected with wild-type or mutant LPL plasmids, measuring mRNA/protein expression and enzymatic activity. RESULTS: Clinically, Proband 1 exhibited recurrent pancreatitis with moderate hyperglycemia, whereas Proband 2 had extreme HTG without pancreatitis but with severe insulin resistance, reflecting variable expressivity. Two LPL missense variants, c.1187A>T (p.Glu396Val) and the novel c.1251G>C (p.Trp417Cys), both located in exon 8. Both affected residues were highly conserved and localized to the C-terminal domain by AlphaFold-based mapping. NetCGlyc predicted Trp417 as a potential C-mannosylation-related residue. Mutant LPL mRNA and protein expression were comparable to wild-type, whereas enzymatic activity was significantly reduced in cell lysates and culture medium. CONCLUSIONS: These findings provide functional evidence that p.Glu396Val and the novel p.Trp417Cys impair LPL enzymatic activity despite preserved protein abundance, supporting a qualitative functional defect. Our findings highlight the value of functional validation and metabolic assessment in interpreting heterozygous LPL variants in HTG.