The COGA investigators divided their samples into two groups—an initial study sample and a larger replication sample—and conducted independent genomic screens with both groups. The initial sample entailed a complete genome survey of 987 members of 105 multi-generational families that were severely affected with alcohol dependence. The investigators then analyzed 292 genetic markers located across the genome in 382 affected sibling pairs. This analysis found evidence that specific markers located on chromosomes 1, 2, and 7 were linked with alcohol dependence (Reich et al. 1998), thereby suggesting multiple DNA regions that then could be searched in more detail to identify specific candidate genes for the development of alcohol dependence.
