The present study investigated the possible correlation of SLC6A4 polymorphisms (5-HTTLPR, rs25532, rs25531) in Iranian OCD patients considering gender, age of onset, family history of psychiatric disorders, obsessive and compulsive subtypes and severities.
The higher expressing 5-HTTLPR/rs25531 LA allele was more prevalent in TD probands than in controls (χ(2) = 5.75; P = 0.017; odds ratio [OR], 1.35); and, in a secondary analysis, surprisingly, it was significantly more frequent in probands who had TD alone than in those who had TD plus OCD (Fisher's exact test; P = 0.0006; OR, 2.29).
A noteworthy lack of association at the LPR, LPR-rs25531 and rare 425V variants suggests that hypotheses about OCD risk need revision to accommodate these new findings, including a possible gender effect.
No significant association of OCD with the 5-HTTLPR genotype was found even on inclusion of the rs25531 locus, which is part of the transcription factor binding site as reported in earlier studies.
Subgroups based on the age of OCD onset, gender, familiality, factor analysis-derived symptom dimensions, or comorbidity with other psychiatric disorders failed to identify SLC6A4- or BDNF-associated phenotypes, with one exception of overall number of comorbid anxiety disorders being significantly associated with 5-HTTLPR/rs25531.
Likewise, the higher expressing LAC haplotype (5-HTTLPR/rs25531/rs25532) was more frequent in TD probands than in controls (P = 0.024; OR, 1.33) and also in the TD alone group versus the TD plus OCD group (P = 0.0013; OR, 2.14).
Haplotype-based testing of rs25532 and all other known non-coding functional SLC6A4 variants revealed a highly significant omnibus association with OCD in a large case-control sample.
On the other hand, combined genotypes of SLC6A4 rs16965628 GG+GC were found to be risk fac</span>tors for OCD development (p=0.02, OR=3.464; 95% CI 1.214-9.883) in logistic regression analysis adjusted for age and gender.
Thus, the cumulative count of SERT I425V becomes 1.57% in OCD/TD spectrum conditions versus 0.15% in controls, with a recalculated, family-adjusted significance of χ(2) = 15.03 (P < 0.0001; OR, 9.0; total worldwide genotyped, 2914).
Similarly, three individuals (two with OCD/OCPD) carried the rare I425V SLC6A4 variant, but none of them passed it on to their six OCD-affected offspring, suggesting that it is unlikely to be solely responsible for the 'OCD plus syndrome', as reported by Ozaki et al.