DNA was collected following published procedures (Freeman et al., 1997; Walker et al., 1999). Participants swabbed their cheeks with 3 cotton swabs, followed by a rinse of the mouth with 10 ml of sucrose solution (4% in tap water). All genotyping was conducted at the Neurogenetics Laboratory at theMind ResearchNetwork (Albuquerque, NM). Genomic DNA was isolated from buccal cells using a modification of published procedures (Lench et al., 1988; Spitz et al., 1996). An ABI PRISM 7500 instrument was used to conduct 5′-nuclease (TaqMan) assays of the GABRG1 SNP using assays commercially available from Applied Biosystems (Foster City, CA). This method relies on allele-specific hybridization of oligonucleotide probes (Livak, 1999). Polymerase chain reaction amplifications failed to provide genotypes for rs1391166 in 12 samples and for rs1497571 in 2 samples, despite repeated attempts. For quality control purposes, 34 samples (27%) were genotyped twice for rs1391166 and 20 samples (16%) were genotype twice for rs1497571. Analyses revealed 100% agreement in genotype calls for both SNPs. As an additional check on allele frequencies and genotyping we have reanalyzed every sample for the rs1497571
