Familial chylomicronemia syndrome (FCS) is a rare disorder of triglyceride (TG) metabolism caused by loss of function variants in one of five known canonical genes involved in chylomicron lipolysis and clearance—LPL, APOC2, APOA5, LMF1, and GPIHBP1. This evidence concerns the gene APOA5 and familial chylomicronemia syndrome.