Elevated lipoprotein(a) [Lp(a)] concentrations are positively correlated with premature coronary heart disease (CHD) and are thought to reflect allelic variation in apolipoprotein(a) [apo(a)], the protein unique to Lp(a). Apolipoprotein(a) exists in polymorphic forms that exhibit different apparent molecular masses.
We used a 3-15% gradient polyacrylamide gel electrophoresis in sodium dodecyl sulfate (SDS-PAGE) meth­od followed by immunoblotting to separate and visualize apo(a) forms present in plasma from 180 healthy Macedonian blood donors. One or two isoforms (relative molecular mass from 417,000 to 785,000) were present in each individual. On the hypothesis that apo(a) polymorphism is controlled by different alleles at a single locus, the frequency of the six alleles determined from the observed phenotypes was: LpB = 0.022, Lp^S1 = 0.028, Lp^S3 = 0.201, Lp^S4 = 0.397, Lp^>S4 =0.110, Lp^O = 0.242. These fit the expectations of the Hardy-Weinberg equilibrium in this population. A significant inverse correlation was found between plasma Lp(a) levels and the size of Apo(a) isoforms [Pearson’s correlation coefficient (r) = –0.3477, p <0.001]. A highly skewed distribution of Lp(a) toward lower levels in the Macedonian population may be explained by the high frequencies of alleles for large apo(a) isoforms and the null allele.
Key words: Lipoprotein(a) [Lp(a)]; Apolipoprotein(a) [apo(a)]; Isoforms; Apo(a) allele; Polymorphism(s)