A rare STAP1 mutation incompletely associated with familial hypercholesterolemia.

Autosomal dominant hypercholesterolemia, being referred to as familial hypercholesterolemia (FH), is mainly due to defective LDL receptor (LDLR) function, but is also associated with variants in genes encoding APOB (LDLR ligand) and PCSK9, the catabolic regulator of LDLR. The signal-transducing adaptor family member 1 (STAP1) gene has been recently linked to FH. We describe the case of a 56-year-old male patient found to have hypercholesterolemia at age 34, but who did not continue follow-up nor received treatment with lipid-lowering drugs. At age 55 he suffered a myocardial infarction. A systematic NGS analysis did not show point mutations in the LDLR, APOB, LDLRAP1, or PCSK9 genes, nor large rearrangements of the LDLR gene, but revealed the heterozygous missense variant rs199787258 of STAP1 (c.526C > T; p.Pro176Ser). This variant was also found in heterozygosis in the two siblings of the index case, who also had hypercholesterolemia, but did not cosegregate in his progeny. A bioinformatics analysis and available structural information predicts p.Pro176Ser as the most damaging of all STAP1 missense variants associated with familial hypercholesterolemia. Our findings confirm and extend the linkage between STAP1 variants and FH, and point to an important role of this adaptor protein within a signaling pathway that affects cholesterol homeostasis.