Submitted on January 17, 2003
Revised on February 28, 2003
Accepted on March 4, 2003
Familial hypobetalipoproteinemia: a review
Gustav Schonfeld
Atherosclerosis, Nutrition and Lipid Research, Washington University School of Medicine, St. Louis, MO 63110
Corresponding Author: gschonfe{at}im.wustl.edu
Abstract We review the genetics and pathophysiology of familial hypobetalipoproteinemia [FHBL], a mildly symptomatic genetically heterogeneous autosomal trait. The minority of human FHBL is caused by truncation-specifying mutations of the APOB gene on chromosome 2. In seven families linkage to chromosome 2 is absent, instead linkage is to chromosome 3 [3p21]. In others linkage is absent to both APOB and to 3p21. ApoB100 levels are ~25% of normal, instead of the 50% expected based on the presence of one normal allele, due to reduced rates of production. The presence of the truncating mutation seems to have a "dominant recessive" effect on apoB100 secretion. Concentrations of apoB truncations in plasma differ by truncation, but average at ~10% of normal levels. Lipoproteins bearing truncated forms of apoB are cleared more rapidly than apoB100 particles. In contrast with apoB100 particles cleared primarily in liver via the LDL receptor, most apoB truncation particles are cleared in renal proximal tubular cells via megalin. Since apoB defects cause a dysfunctional VLDL-triglyceride transport system, livers accumulate fat. Hepatic synthesis of fatty acids is reduced in compensation. Informational lacunae remain about genes affecting fat accumulation in liver, and the modulation of liver fat in the presence apoB truncation defects.
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