5-HT polymorphisms and response to SSRIs in OCD Corregiari FM et al. this study, the evaluated groups were extreme. Non- responders were unresponsive to at least three different SRIs and remained symptomatic; responders met tight remission criteria; and controls (healthy volunteers) who neither mental health nor major medical problems. Many putative patients and volunteers were excluded. These strict criteria may have increased the study power but decreased the external validity. Because the data can be interpreted as false positive (at the 0.01 level of significance), further investigations using a larger sample size are necessary to confirm our results. Prospective studies with larger sample sizes and using selection criteria according to the subjects’ genotype would be interesting. In addition, the examined polymorphisms may be in linkage disequilibrium with yet to be identified markers or genes that contribute to OCD. Additionally, further research should be performed to evaluate whether the endocrine response to citalopram can be considered an endophenotype. CONCLUSIONS The conclusions of this study are as follows: (1) The T allele of the 5-HTR2A T102C polymorphism was more frequent among OCD patients. (2) The CC genotype of the HTR2A C516T polymorphism was more frequent among OCD patients who were nonresponsive to several SRI trials than among the SRI- responsive patients. (3) The CC genotype of the HTR1B G681C polymorphism was associated with higher cortisol and prolactin responses to citalopram and a higher platelet-rich plasma serotonin concentration among health volun- teers. However, this pattern was not observed among nonresponsive OCD patients with the same genotype after chronic SRI treatment. ACKNOWLEDGMENTS This research was supported by FAPESP (Fundac¸a˜o de Amparo a` Pesquisa do Estado de Sa˜o Paulo) grant number 99/00170-4. We thank Elisabete Miracca for technical support. 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