DNA inversion within the apolipoproteins AI/CIII/AIV-encoding gene cluster of certain patients with premature atherosclerosis.

The genes coding for apolipoproteins (apo) AI, CIII, and AIV, designated APOA1, APOC3, and APOA4, respectively, are closely linked and tandemly organized in the long arm of the human chromosome 11. A DNA rearrangement involving the genes encoding apoAI and apoCIII in certain patients with premature atherosclerosis has been associated with deficiency of both apoAI and apoCIII in the plasma of these patients. Structural characterization of the genes for apoAI and apoCIII in one of these patients indicates that this rearrangement consists of a DNA inversion containing portions of the 3' ends of the apoAI and apoCIII genes, including the DNA region between these genes. The breakpoints of this DNA inversion are located within the fourth exon of the apoAI gene and the first intron of the apoCIII gene. Thus, this DNA inversion results in reciprocal fusion of the apoAI and apoCIII gene transcriptional units. Expression of these gene fusions in cultured mammalian cells results in stable mRNA transcripts with sequences representing fusions of the apoAI and apoCIII mRNAs. These results indicate that absence of transcripts with correct apoAI and apoCIII mRNA sequences causes apoAI and apoCIII deficiency in the plasma of these patients and suggest that these apolipoproteins are involved in cholesterol homeostasis and protection against premature atherosclerosis.