The GABRG1 genomic region, including 5 kb upstream and 1 kb downstream, was retrieved from NCBI Human Genome Build 35.1. Genotype data from the most diverse population, Africans, were obtained from the HapMap Project Public Release #18 to construct the GABRG1 haplotype structure using SNPHAP (http://www-gene.cimr.cam.ac.uk/clayton/software/snphap.txt). To select minimum index SNPs that represent maximal haplotype structures information, a program based on a double classification tree search algorithm was used (Zhang et al, 2004). On this basis, 24 SNPs spanning GABRG1 were selected (Figure 1). Genotyping was performed using SNPlex (Tobler et al, 2005). Allele-specific probes and optimized multiplexed assays for the 24 SNPs were designed by an automated multi-step pipeline (Applied Biosystems (ABI): http://www.appliedbiosystems.com). SNPlex was carried out on fragmented gDNA (88ng/well) according to the manufacturer’s protocols. Samples were run on the 3730 DNA Analyzer (ABI) and data were analyzed using Gene Mapper v. 4.0 software (ABI). Genotype analysis was performed based on the SNPlex_Rules_3730 method following the factory default rules. Genotyping included 21% duplicates.
