It is a classical monogenic disorder that follows autosomal recessive inheritance and results from rare biallelic variants in one of five canonical genes, namely LPL, APOC2, APOA5, LMF1, and GPIHBP1. In contrast, MCM is at least 50–100-times as common as FCS and represents the large majority of molecularly defined patients with severe hypertriglyceridemia. The gene discussed is LMF1; the disease is hypertriglyceridemia.