In conclusion, our results provide limited support for an association between rs9291283 and CD in adolescence/young adulthood and AAD in adulthood. Unfortunately, we did not replicate previous findings showing associations between rs279871 and rs279858 with adolescent CD and adult AAD, respectively. However, perhaps the more important implication here is the importance of replication and combining studies. There is an increasing literature on negative and non-replicated findings and the field of behavior genetics has yet to identify the reasons for this (Hewitt 2012). There are many possibilities, including differences in sample ascertainment, assessment, as discussed above. It is equally likely that many of the initial positive associations are false positives, and this study demonstrates the utility of including an independent replication sample in the study design, so that the results from an individual sample can be weighted in the context of their reproducibility.
