Once linkage analyses have identified chromosome regions contributing to alcohol dependence, the next step is to examine individual candidate genes that are known to be located in those regions. This is typically done using gene association studies. In contrast to linkage studies, which examine whether relatives with a disorder share a given marker more often than expected by chance, association studies consider whether a particular variant of a gene is found more often in people with the disorder than in people without the disorder. Whereas linkage studies identify relatively large chromosomal regions that can contain numerous genes as contributors to the development of the disorder, association studies detect significant effects over smaller DNA regions and can be used to identify specific genes which contribute to the development of the disorder. Moreover, whereas linkage analyses must be conducted with relatives, association studies can be performed using either families or unrelated probands and controls.
