APOB Gene

The APOB gene (APOB stands for "apolipoprotein B") is a protein-coding gene located on chromosome 2p24.1. The product encoded by this gene, apolipoprotein B, is the major apolipoprotein of chylomicrons and low-density lipoproteins (LDL). It is the ligand for the LDL receptor.

Apolipoprotein B occurs in plasma in two major isoforms:

• ApoB-48 (synthesized exclusively in the intestine)
• and
• ApoB-100 (synthesized in the liver).

The intestinal and hepatic forms of ApoB are encoded by a single gene and a single, very long mRNA. The two isoforms share a common N-terminal sequence. The shorter ApoB-48 protein is formed after RNA editing of the ApoB-100 transcript at residue 2180 (CAA->UAA), creating a stop codon and terminating translation early.

Mutations in this gene or its regulatory region cause hypobetalipoproteinemia, normotriglyceridemic hypobetalipoproteinemia, and hypercholesterolemia due to ligand defects in ApoB, diseases that affect plasma cholesterol and ApoB levels.

1. Berger G et al. (1983) Apolipoprotein B detected in the plasma of a patient with homozygous hypobetalipoproteinaemia: implications for aetiology. J Med Genet 20: 189-195.
2. Biemer JJ et al (1975) The genetic relationship of abetalipoproteinemia and hypobetalipoproteinemia: a report of the occurrence of both diseases within the same family. J Lab Clin Med 85: 556-565.
3. Brown BJ et al.(1974) Familial hypobetalipoproteinemia: report of a case with psychomotor retardation. Pediatrics 54: 111-113.