Apolipoprotein E phenotypes and hyperlipidemia

Summary Apolipoprotein E phenotypes were determined in 361 patients with hyperlipidemia and in controls. The E2 isoform was significantly more frequent in the group of hyperlipidemics (P<0.0005). This was not due to a higher frequency of E-2/2 homozygotes with type III hyperlipoproteinemia, but rather to a significantly higher frequency of E2 heterozygotes (P<0.0005). Subgrouping of hyperlipidemics into patients with a) hypertriglyceridemia, b) hypercholesterolemia and c) mixed hyperlipidemia revealed i) that isoform E2 was significantly more frequent in patients with hypertriglyceridemia (0.001>P>0.005), ii) that isoform E4 was significantly more frequent in patients with hypercholesterolemia (0.01>P>0.005) and iii) that isoforms E2 (P>0.005) and E4 (0.05>P>0.025) were both more frequent in patients with mixed hyperlipidemia. Roughly 20% of patients with mixed hyperlipidemia had one of the rare phenotypes E-4/4,-4/2 or-2/2. We conclude that alleles 2 and 4 both contribute to the susceptibility for, and/or phenotypic expression of hyperlipidemia. Whereas the gene 2 seems to exert its influence on plasma lipoproteins by an abnormal gene product (E2) that has reduced binding activity to lipoprotein receptors, the mechanism underlying the association of the 4 gene with hyperlipidemia is presently unclear.