| Summary: | <p>Abstract</p> <p>Background</p> <p>Conflicting associations with heroin dependence have been found involving the A1 allele of dopamine D2 receptor gene (<it>DRD2</it>) <it>Taq</it>I A polymorphism.</p> <p>Methods</p> <p>We compared two samples of unrelated Spanish individuals, all of European origin: 281 methadone-maintained heroin-dependent patients (207 males and 74 females) who frequently used non-opioid substances, and 145 control subjects (98 males and 47 females).</p> <p>Results</p> <p>The A1-A1 genotype was detected in 7.1% of patients and 1.4% of controls (<it>P </it>= 0.011, odds ratio = 5.48, 95% CI 1.26–23.78). Although the A1 allele was not associated with heroin dependence in the entire sample, the frequency of A1 allele was higher in male patients than in male controls (24.4% vs. 16.3%, <it>P </it>= 0.024, odds ratio = 1.65, 95% CI 1.07–2.57). A logistic regression analysis showed an interaction between <it>DRD2 </it>alleles and gender (odds ratio = 1.77, 95% CI 1.15–2.70).</p> <p>Conclusion</p> <p>Our results indicate that, in Spanish individuals, genotypes of the <it>DRD2 Taq</it>I A polymorphism contribute to variations in the risk of heroin dependence, while single alleles contribute only in males.</p>
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