Quantitative trait locus analysis

Alcoholism is a quantitative disorder that is caused by the combined influe nces of numerous genes (i.e., quantitative trait loci [QTLs]) and environme ntal factors. To identify QTLs for alcoholism, researchers compare subject groups (e.g, inbred mouse strains) that differ in both their genetic makeup (i.e, genotype) and alcohol-related trait (e.g., sensitivity to certain al cohol effects). Using statistical tests one can then determine whether a sp ecific gene or DNA region contributes to the trait of interest. This strate gy requires that the relevant gene exists in several variants (i.e, is poly morphic). To conduct such QTL analyses, researchers study either a large po pulation of mice that all differ in their genotypes or compare several stra ins, each of which has a fixed genotype. However, QTL analyses still have s everal limitations. Nevertheless, such studies already have identified seve ral DNA regions and genes that may affect the response to alcohol and thus may contribute to the risk for alcoholism.