No association between the dopamine D-2 receptor TaqI A1 allele and earlier age of onset of alcohol dependence according to different specified criteria

Background: The presence of the Al allele of the dopamine D, receptor TaqI restriction fragment length polymorphism has been reported to be associated with an earlier age of onset of alcohol dependence as a marker for severit y. Methods: We tested this hypothesis with special regard to the definition of the age of onset of alcoholism in 243 patients with alcohol dependence, ac cording to DSM-IV criteria assessed by the standardized interview Munchner Composite International Diagnostic Interview (M-CIDI), consecutively admitt ed for detoxification. Additionally, the Addiction Severity Index (ASI) was performed. The TaqIA polymorphism was amplified by polymerase chain reacti on (PCR), and the PCR product was digested by the restriction enzyme TaqI. Patients were subsequently divided into an A1 (presence of at least one A1 allele, n = 88) and an A2 group (absence of an A1 allele, n = 155). The fol lowing criteria for different definitions of age of onset were used: (1) ag e of onset of the first occurring symptom necessary for the diagnosis of al cohol dependence according to M-CIDI; (2) age of onset of the last symptom of alcohol dependence according to M-CIDI; (3) age of onset of more than 3 drinking days per week on a regular basis according to ASI; (4) age of onse t of more than 3 drinking days - of more than five drinks per drinking day- or at least one binge drinking episode per week on a regular basis accordi ng to ASI. Results: The frequency of the A1 allele in our patient sample was 0.208. No statistically significant association between the Al allele and the age of onset of alcoholism was found. The mean age of onset according to criterio n 1 was 30.4 +/- 10.8 years for the A1 group and 30.2 +/- 10.2 years for th e A2 group (p = 0.89); for criterion 2, it was 33.3 +/- 10.0 years for the A1 group and 33.9 +/- 10.2 years for the A2 group (p = 0.77); for criterion 3, it was 18.0 +/-: 7.5 years for the A1 group and 18.1 +/- 6.1 years for the A2 group (p = 0.92); and for criterion 4, it was 22.3 +/- 9.7 years for the A1 group and 21.8 +/- 8.5 years for the A2 group (p = 0.76). Conclusions: No association was found between the A1 polymorphism and age a t onset of alcohol dependence according to different specified criteria.