The enzyme lipoprotein lipase plays a central role in the processing of energy in the form of calorically dense triglyceride. Classical LPL deficiency usually presents in childhood with the multiple manifestations related to chylomicronemia. Many patients with genetic variations have been noted who differ in one of many ways from the classical patients. With the development of techniques to measure enzyme mass and to study gene expression, the molecular defects in each of these families should become evident.