In the area of alcohol dependence, two genes that we have focused on that come out of the gene identification efforts from the Collaborative Study on the Genetics of Alcoholism (COGA) are GABRA2 and CHRM2. Both genes were targeted because they were plausible biological candidates located near linkage peaks observed in the COGA sample. Chromosome 4 repeatedly emerged with linkage to alcohol dependence diagnoses, quantitative drinking measures, and electrophysiological measures (that are believed to represent endophenotypic markers of a predisposition toward alcohol problems and other externalizing disorders) (Porjesz et al., 2002; Reich et al., 1998; Saccone et al., 2000; Williams et al., 1999). Located under the chromosome 4 linkage peak was a cluster of GABA-A receptor genes. These genes were considered good candidates for potential involvement in alcohol dependence, as evidence from animal, human, and in vitro cell models suggested that Aminobutyric acid (GABA), the major inhibitory neurotransmitter in the human central nervous system, is involved in many of the neurochemical pathways affecting alcohol use and related disorders (Buck, 1996; Grobin et al., 1998). Genetic markers were tested across the
