THE HNA-3a/b polymorphism is closely associated with a mutation in the CTL2 gene (SLC44A2). (A) Genome-wide SNP analysis of DNA from 8 unrelated HNA-3a–negative and 107 random persons. Each of the HNA-3a–negative subjects possessed AA at SNP rs2288904, whereas the distribution of A and G at the same position in random subjects corresponded to that expected for Hardy-Weinberg distribution of 2 alleles with gene frequencies of 0.21 and 0.79, respectively. (B) HNA-3a/b phenotypes and G>A542 genotypes in 16 subjects. Without exception, the HNA-3a/a, HNA-3a/b, and HNA-3b/b phenotypes correlated with the presence of GG, GA, and AA, respectively, at SNP rs2288904. (C) Representative DNA sequencing results for the G>A542 SNP in persons with phenotypes HNA-3a/3a, HNA-3a/3b, and HNA-3b/3b.