All of these findings should be interpreted with caution. The sample sizes in all three studies were quite small. Nevertheless, given that Willour et al138 observed suggestive linkage to the same chromosome 9p region as reported by Hanna et al is noteworthy. In addition, as discussed above, four independent studies have reported an association of OCD and the glutamate transporter which is located in this region on 9p. Thus, the findings from the two studies by Hanna and colleagues135,137 and the one reported by Willour et al138 suggest that there may be a susceptibility locus in this region of 9p. Unfortunately, this region did not show any evidence for linage in the study completed by Shugart et al.136
