Apolipoprotein (apo) A-I is the major protein of HDL cholesterol, whereas apoC-III and apoA-IV are minor components. The genes coding for apoA-I, apoC-III, and apoA-IV are adjacent to one another on the long arm of chromosome 11. Familial apolipoprotein gene cluster deletion syndrome has been described in 1 family and found to be a homozygous deletion of the entire APOA1/C3/A4 gene complex. This results in a lack of expression of these plasma lipoproteins, with marked HDL-C deficiency in the homozygote and approximately half-normal levels of these apolipoproteins and HDL-C in the heterozygotes. [from
OMIM]