can be investigated (Lesch et al., 2008). Furthermore, using controls unscreened for the presence of psychiatric disorders can be expected to reduce power, though the effect of this is modest, given that the prevalence is at most 5% (McCarthy et al. 2008). The X-chromosome was not analyzed in most of the studies, due to a limitation of the FBAT-program. As a clear difference in prevalence of ADHD exists between genders, this might still be an interesting target to look at.
