Human LPL is a glycoprotein enzyme with a molecular mass of 61 kDa, and it plays a key role in regulating the triglyceride (TG) levels in circulation by hydrolyzing TGs in TG-rich lipoproteins at the first step in their metabolism. Homozygous or compound heterozygous LPL deficiency causes severe fasting hypertriglyceridemia. Heterozygous LPL deficiency usually results in a normolipidemic state, but this may cause mild hypertriglyceridemia if heterozygotes are exposed to factors, such as high alcohol intake and/or a hyperinsulinemic state. Severe fasting hypertriglyceridemia is mainly caused by abnormalities of the LPL gene, whereas there are some cases caused by gene defects relating to synthesis and transport of LPL such as LMF and GPIHBP1, and by an autoantibody to LPL acting as inhibitor of LPL.