Quantitative trait locus analysis of candidate gene alleles associated with attention deficit hyperactivity disorder (ADHD) in five genes: DRD4, DAT1, DRD5, SNAP-25, and 5HT1B

It has been widely postulated that the categorical diagnosis of attention deficit hyperactivity disorder (ADHD) should be seen as the extreme end of a set of traits quantitatively distributed in the general population. A consequence of this is that the genes associated with DSM‐IV ADHD should also influence these underlying traits in non‐affected individuals. The aim of this study was to examine if specific candidate loci previously shown to be associated with DSM‐IV ADHD, also act as quantitative trait loci (QTLs) for ADHD‐symptoms in the general population. We have genotyped five candidate markers in a population‐based sample of male dizygous twin‐pairs (n = 329 pairs). We found little evidence to support a role for the previously‐nominated alleles of a DRD4 VNTR, a 5HT1B SNP, or a microsatellite marker near to DRD5, in the distribution of ADHD‐symptoms scores; however, we found some evidence to suggest that the DAT1 3′UTR VNTR and weak evidence that a microsatellite in SNAP‐25 may have a role in continuous measures of ADHD‐symptoms hyperactivity above and beyond their role in clinical ADHD