The allele frequencies of SLCO1B1, ABCC2, ABCG2, and ABCB11 variants are
summarized in Table 1. The SLCO1B1 388G (*1b) variant was more common in AfricanAmericans than in European-American participants (77 vs. 38% allele frequency, P <
0.001). On the other hand, the SLCO1B1 521C (*5) variant had a relatively high allele
frequency in European-American participants than African-American participants (15 vs.
1%, P = 0.008), in line with our previous work [5]. Haplotype analysis revealed the 521C
variant was most likely to occur in conjunction with the 388G allele to form SLCO1B1*15
(combination of *1b and *5), consistent with several recently published observations in
Japanese and European Caucasian populations (Table 3) [7, 13]. The 1463C (*9) variant,
initially identified with a relatively high allele frequency in African-Americans [5], was only
identified with a 1% allele frequency in the current study, indicating this variant may be less
common in African-Americans than previously thought.