Over 80 candidate gene studies have been published over the last decade (Table III) . As noted above, association studies have examined candidate genes that function within the serotonergic and dopaminergic systems and more recently the glutamatergic system based on knowledge of the pathophysiology and pharmacology of OCD. However, with the exception of the glutamate transporter gene SLCL1A1,81-84 none have been consistently replicated. While some of the more recent published studies have larger sample sizes, all have inadequate sample sizes to achieve genome -wide significance (ie, 5x10-8). Some recent studies have moved beyond simply documenting that individuals with OCD are more likely to have a specific allele or candidate gene that other nonaffected individuals (ie, association studies) and have begun to explore the function of some of the genes being studied. Preliminary results suggest that may be a promising approach.85 However, none of these studies have yet been replicated, so it is too early to reach any definite conclusions.
