No association between dopamine D2 receptor (DRD2) alleles and crack/cocaine dependence in Brazilians

Introduction: The causal mechanisms behind crack/cocaine use are still unknown, but genetic influences are suggested. Objective: To investigate the relationship between the genetic polymorphism TaqI (rs1800497) in the dopamine D2 receptor (DRD2) gene and susceptibility to crack/cocaine dependence in a group of addicts to crack/cocaine and a non-addicted group. Methods: The case group (n=515) was composed of crack/cocaine-dependent men and the control group (n=106) comprised men who were considered not dependent on crack/cocaine. The oral hygiene habits, decayed, missing, and filled teeth index, gingival index, and plaque index were evaluated. The reference single nucleotide polymorphism (rs1800497 C/T) of the DRD2 gene was genotyped by a real-time polymerase chain reaction technique. Student’s t-tests for independent samples or the non-parametric Mann-Whitney test were used to compare groups regarding quantitative variables. Results: The case group showed a mean time of 9.91±7.03 years of crack use, and 61.06±92.96 stones/week. The socio-demographic profile of the sample was White, single men, with basic education, blue-collar worker, smoker, and reporting alcohol use. There was a high frequency of gingival inflammation, plaque accumulation, and caries experience. For all genetic models tested, there was no significant difference in the genotypic frequency in rs1800497 of the DRD2 gene, between case and control groups (p>0.05). Conclusion: The genetic variant in the DRD2 did not increase the vulnerability to develop crack/cocaine dependence. The complex genetic nature of crack/cocaine dependence and a large variation of DRD2 allele frequencies, depending on the population group sampled, could be one explanation for the no association.