[Dopamine D2 and D4 receptor genes distinguish the clinical presence of tics in obsessive-compulsive disorder]

An allelic association study between dopamine receptor gene polymorphisms D2 (DRD2) and D4 (DRD4), in obsessive-compulsive patients (OCD) with or without chronic motor or vocal tics (OCD+ or OCD-) was performed. Molecular genotypes were obtained using the polymerase chain reaction method (PCR) in 66 patients diagnosed according DSMIV criteria, 12/66 OCD patients presented tics, 54 Control subjects were also typed. OCD patients with tics compared to control had a higher frequency of TaqI A2 allele (p = 0.014); and an excess of homozygous individuals A2A2 (p = 0.001). In DRD4 genes polymorphisms, allele 7 showed a higher prevalence and frequency in those OCD+ tics compared to OCD- tics (91% vs. 48%). Most of the OCD patients with tics compared to those without tics showed an increased frequency of the DRD2-A2 (58% vs 27% respectively, p = 0.048) as well as an increased frequency of the DRD4-7-fold variant (48% in OCD with tics vs 9% in OCD without tics, p = 0.018). Similarly, when both alleles were combined (at least one copy of DRD2-A2 and DRD4-R7), patients with tics showed a higher frequency of this haplotype (83.3% vs. 40%, p = 0.016). OCD patients with tics may represent a different clinical and genetic subtype of the disorder.