on neuropsychological performance (Doyle et al. 2005; Rommelse 2008) and those based on neuroimaging (Castellanos and Tannock 2002), i.e. brain activity and structure. Recent genome-wide linkage studies of neuropsychological endophenotypes for ADHD indeed suggest that these measure offer increased power for finding loci compared to clinical phenotypes (Doyle et al. 2008; Rommelse et al. 2008c). A pooled GWAS on memory performance also suggests this (Papassotiropoulos et al. 2006). ‘Imaging genetics’ studies would be thought to be particularly powerful, requiring even smaller sample sizes (Dreher et al. 2008; van Haren et al. 2008). Studies using such ADHD endophenotypes for GWAS are currently ongoing.
