Association between early-onset alcoholism and the dopamine D2 receptor gene

We examined the allelic association between the dopamine D2 receptor (DRD2) gene and alcoholism in 100 biologically unrelated Japanese alcoholics and 93 unrelated controls. Genomic DNA was prepared from peripheral white blood cells using the phenol-chloroform method. A 310-bp region surrounding the TaqA site at the DRD2 locus was amplified by polymerase chain reaction (PCR), and the PCR product was incubated with TaqI. The A1 allele remained intact while the A2 allele was cut. The frequency of the A1/A1 genotype and the frequency of the A1 allele were higher in early-onset alcoholics than in controls, P < 0.05 and P < 0.01, respectively. Moreover, the frequency of the A1/A1 genotype and the frequency of the A1 allele were higher in early-onset alcoholics with family histories of alcohol dependence than in controls, P < 0.01 and P < 0.01, respectively. The results indicate that the DRD2 gene is associated with susceptibility to early-onset alcoholism, and that each additional A1 allele shifts onset of alcoholism to an earlier age.