Unusual familial lipoprotein C-III associated with apolipoprotein C-III-O preponderance.

Among 256 consecutive subjects so far studied in our laboratory, we found one subject (a 63-year-old female) whose very low density lipoprotein (VLDL) and high density lipoprotein (HDL) contained unusually high amounts of apolipoprotein C-III-O among apolipoprotein C-III polymorphic forms. Identification of apolipoprotein C-III-O was achieved by a combination of basic polyacrylamide gel electrophoresis, isoelectric focusing and sialidase treatment of plasma apolipoproteins. This unusual lipoprotein was inherited by two of her four children without the manifestation of clinical symptoms. Triacylglycerols and cholesterol concentrations of VLDL, low density lipoprotein (LDL) and HDL fractions, and serum apolipoprotein C-III levels of the three subjects with apolipoprotein C-III-O were within the normal range, as estimated by rocket immunoelectrophoresis. Our results clearly demonstrated that the unusual lipoproteins with the preponderance of apolipoprotein C-III-O among apolipoprotein C-III polymorphic forms were genetically determined. These cases may be a new type of genetic lipoprotein disorder.