The GABRA2 haplotype block structure is shown in Figure 1. Although the African American haplotype block structure is not as well defined as in Caucasians, African Americans nevertheless have the same two haplotype blocks with a region of recombination in intron 3. Logistic regression analyses were performed with the distal block (block 2) haplotypes, since this is the GABRA2 region that has previously been associated with alcohol and drug dependence (12–21).
