K. Deprince et al., Genetic effect of two APOA repeat polymorphisms (Kringle 4 and pentanucleotide repeats) on plasma Lp(a) levels in American Samoans, HUMAN BIOL, 73(1), 2001, pp. 91-104
Elevated plasma lipoprotein(a) [Lp(a)] level has been established as an ind
ependent risk factor for atherosclerosis and coronary heart disease. Consid
erable ethnic group differences in the distribution of plasma Lp(a) levels
have raised public health concerns. Recently. we have reported that Samoans
have the lowest plasma Lp(a) levels of any population group. In the presen
t investigation, we report the contribution of two apolipoprotein(a) (APOA)
polymorphisms, the kringle 4 type 2 (K4) repeat and the pentanucleotide re
peat (PNR), in affecting plasma Lp(a) levels in an American Samoan sample (
n = 309). The K4 repeats ranged in size from 15 to 40. The common alleles c
ontained repeals ranging from 26 to 36 with allele frequencies between 5.5%
to 9.7%, and these accounted for 82% of all alleles. An inverse relationsh
ip between K4 repeat number and plasma Lp(a) level was observed for single-
banded (r = -0.59, p = 0.0001) and double-banded phenotypes (r = -0.50, p =
0.0001), This polymorphism explained 60% of the variation in plasma Lp(a)
level in American Samoans. For the PNR polymorphism. five different repeat
alleles and eight different genotypes were identified, the most common alle
le was eight repeats. The *8 PNR allele was associated with a wide range of
K4 repeats, the *9 PNR allele with larger K4 repeats (25-40), and the *10
PNR with smaller K4 repeats (15-24). Analysis of variance (ANOVA) revealed
that the PNR polymorphism accounts for 2.1% of the variability in plasma Lp
(a) levels in this sample. when the K4 repeat polymorphism was taken into a
ccount. Our data show that common polymorphisms in the APOA gene are major
determinants of plasma Lp(a) variation in American Samoans.