Combined deficiency of apolipoprotein C-II and lipoprotein lipase in familial hyperchylomicronemia.

The underlying pathophysiological defect was studied in four siblings with familial hyperchylomicronemia. Deficiency of apolipoprotein C-II and E-3 was identified. In addition, these subjects had markedly decreased LPL activity in postheparin plasma. Addition of normal plasma to the assay as source for apoC-II enhanced LPL activity only to a limited extent. In contrast with previously reported patients with apoC-II deficiency, a far less pronounced effect of intravenous infusion of normal plasma was seen in one of the siblings, probably due to the combined deficiency of apoC-II and LPL. Plasma VLDL-TG turnover rate was not decreased in one of the siblings with apoC-II and LPL deficiency, suggesting different metabolic pathways for chylomicrons and VLDL. Family study confirmed an autosomal recessive mode of inheritance both for apoC-II and for apoE-3 deficiency. The mode of inheritance for LPL deficiency could not be established exactly.