Familial hypobetalipoproteinemia caused by a mutation in the apolipoprotein B gene that results in a truncated species of apolipoprotein B (B-31). A unique mutation that helps to define the portion of the apolipoprotein B molecule required for the formation of buoyant, triglyceride-rich lipoproteins.
Apolipoprotein B-100 has a crucial structural role in the formation of VLDL and LDL. Familial hypobetalipoproteinemia, a syndrome in which the concentration of LDL cholesterol in plasma is abnormally low, can be caused by mutations in the apo B gene that prevent the translation of a full-length apo B-100 molecule. Prior studies have revealed that truncated species of apo B [e.g., apo B-37 (1728 amino acids), apo B-46 (2057 amino acids)] can occasionally be identified in the plasma of subjects with familial hypobetalipoproteinemia; in each of these cases, the truncated apo B species has been a prominent protein component of VLDL. In this report, we describe a kindred with hypobetalipoproteinemia in which the plasma of four affected heterozygotes contained a unique truncated apo B species, apo B-31. Apolipoprotein B-31 is caused by the deletion of a single nucleotide in the apo B gene, and it is predicted to contain 1425 amino acids. Apolipoprotein B-31 is the shortest of the mutant apo B species to be identified in the plasma of a subject with hypobetalipoproteinemia. In contrast to longer truncated apo B species, apo B-31 was undetectable in the VLDL and the LDL; however, it was present in the HDL fraction and the lipoprotein-deficient fraction of plasma. The density distribution of apo B-31 in the plasma suggests the possibility that the amino-terminal 1425 amino acids of apo B-100 are sufficient to permit the formation and secretion of small, dense lipoproteins but are inadequate to support the formation of the more lipid-rich VLDL and LDL particles.
Young
S G
SG
Gladstone Foundation Laboratories for Cardiovascular Disease, University of California, San Francisco 94140.
Hubl
S T
ST
Smith
R S
RS
Snyder
S M
SM
Terdiman
J F
JF
D000328:Adult; D000368:Aged; D001055:Apolipoproteins B / Q000235:genetics*; D005260:Female; D006579:Heterozygote; D006801:Humans; D006995:Hypobetalipoproteinemias / Q000235:genetics*; D007009:Hypolipoproteinemias / Q000235:genetics*; D008074:Lipoproteins / Q000096:biosynthesis*; D008297:Male; D008875:Middle Aged; D009154:Mutation; D014280:Triglycerides / Q000096:biosynthesis*
D001055:Apolipoproteins B; D008074:Lipoproteins; D014280:Triglycerides