title: The taqI DRD2 A1 allele is associated with alcohol-dependence although its effect size is small.
abstract: BACKGROUND
  Numerous studies of the relationship between the TaqIA DRD2 A1 allele and alcohol-dependence have been performed and many of these have shown an association whereas others have not (Noble, 2003). This has consequently generated some controversy as to whether such an association actually exists (Noble, 2003). In the two recent meta-analyses by Noble (2003) and Young et al. (2004) some very important methodological issues have been discussed, which need to be addressed in forthcoming studies. Thus, the sample size is of great importance. In case-control studies it has been estimated that to detect the role of genes with small effect size of approximately 2, which is in the range of the DRD2 A1 allele-alcoholism relationship, case-control sets of 300-400 subjects are necessary (Noble, 2003).
  
  
  METHODS
  In the present study, we have consequently recruited a large number of subjects, 375 alcohol-dependent individuals, who were treated as inpatients for alcohol withdrawal symptoms and out of these 357 could be evaluated. As controls, 578 individuals screened and 254 individuals unscreened for alcohol consumption were used. Thus, the total number of subjects was 1217.
  
  
  RESULTS
  In the present study, in which the TaqI A1/A2 DRD2 polymorphism was in Hardy-Weinberg equilibrium in the patient group and the two control groups, we found that the TaqI DRD2 A1/A2 genotype frequency differed significantly between the alcohol-dependent group and both the total and screened control groups. Furthermore, the TaqI DRD2 A1 allele frequency was significantly overrepresented in the alcohol-dependent subjects as compared with both the total and screened control groups. The odds ratio for alcohol-dependency being associated with the A1 allele was 1.34.
  
  
  CONCLUSIONS
  Consequently, the findings in this study lend further support to the notion of an association between the DRD2 A1 allele and alcohol-dependence, although the effect size of the DRD2 A1 allele is small.
authors.affiliation: From the Institute of Clinical Neuroscience, Section of Psychiatry, the Sahlgrenska Academy at Göteborg University, Sweden. Claudia.Fahlke@psy.gu.se
authors.forename: Ulf
authors.initials: U
authors.lastname: Berggren
authors.forename: Claudia
authors.initials: C
authors.lastname: Fahlke
authors.forename: Erik
authors.initials: E
authors.lastname: Aronsson
authors.forename: Aikaterini
authors.initials: A
authors.lastname: Karanti
authors.forename: Matts
authors.initials: M
authors.lastname: Eriksson
authors.forename: Kaj
authors.initials: K
authors.lastname: Blennow
authors.forename: Dag
authors.initials: D
authors.lastname: Thelle
authors.forename: Henrik
authors.initials: H
authors.lastname: Zetterberg
authors.forename: Jan
authors.initials: J
authors.lastname: Balldin
mesh_terms: D000328:Adult; D000368:Aged; D000437:Alcoholism / Q000235:genetics*; D000483:Alleles; D016022:Case-Control Studies; D016009:Chi-Square Distribution; D005260:Female; D005787:Gene Frequency; D005838:Genotype; D006801:Humans; D008297:Male; D008875:Middle Aged; D010641:Phenotype; D016133:Polymerase Chain Reaction; D011110:Polymorphism, Genetic; D017448:Receptors, Dopamine D2 / Q000235:genetics*; D013548:Sweden; D019914:Taq Polymerase / Q000235:genetics
chemical_list: D017448:Receptors, Dopamine D2; D019914:Taq Polymerase