HYPERVARIABLE POLYMORPHISM OF APO(A) IN BLACKS AND WHITES AS REFLECTED BY PHENOTYPING

Genetic polymorphism at the apolipoprotein(a) structural locus was inv estigated in 203 American blacks using a high-resolution SDS-agarose e lectrophoresis method followed by immunoblotting, and the gene frequen cy data were compared with a previously screened American white sample using the same method. Between the two samples, a total of 27 discret e APO(a) allelic isoforms have been documented; of these, 24 were comm on to both groups. Of the 203 blacks screened, APO(a) immunoreactive i soforms were detected in 201, with a total of 101 distinct phenotypes (67 (33%) single-banded and 134 (67%) double-banded). A similar level of gene diversity was observed at the APO(a) locus in blacks (93%) and whites (94%). Despite having a similar number of alleles and a simila r level of gene diversity, the frequencies of some APO(a) alleles were significantly different between blacks and whites. Overall, the frequ encies of large-size APO(a) alleles, associated with lower LP(a) level s, were significantly lower (P < 0.0001), while the frequencies of med ium-size APO(a) alleles, associated with intermediate LP(a) levels, we re significantly higher (P < 0.0001) in blacks than in whites. However , the frequencies of small-size alleles, associated with higher LP(a) levels, were comparable between the two race groups. These data indica te that the observed differences in mean LP(a) levels between whites a nd blacks may be accounted for by the size variation at the APO(a) str uctural locus.