Researchers have developed several strategies to identify genes that contribute to differences in the risk for alcohol dependence, including case–control studies and linkage analyses. These strategies depend on the premise that for a particular position in the DNA of these genes, more than one possible form exists. Each of these forms is termed an allele. The study methods used to identify genes that affect the risk for alcohol dependence assume that the presence of certain alleles increases the risk of alcoholism. These variants that affect risk can be located either directly within a gene or near a gene.
