Genome scan linkage mapping projects have identified promising chromosomal regions for AD susceptibility loci, some of which have led to the identification of disease-influencing loci. Linkage studies of AD published by the Collaborative Study on the Genetics of Alcoholism (COGA) group (Reich et al. 1998; Foroud et al. 2000) and by investigators in the Intramural Program of the National Institute on Alcohol Abuse and Alcoholism (NIAAA) (Long et al. 1998) yielded several chromosomal locations with lod scores suggesting that they harbor loci influencing risk for AD. Recruitment for COGA was conducted at six sites in the United States. Participants were ascertained from nuclear and extended pedigrees containing at least two alcohol-dependent first-degree relatives in addition to an alcohol-dependent proband. The NIAAA study ascertained participants from among members of a Southwestern American Indian tribe. Both groups reported data consistent with loci influencing risk for AD mapping in the vicinity of an alcohol dehydrogenase (ADH) gene cluster on chromosome 4q (see below). Several other linkage peaks, even those that did not meet standard criteria for genomewide significance, have led to the identification
