New evidence, supporting an association between attention deficit hyperactivity disorder and the DRD5 locus in the IRISH population

Abnormalities in the dopaminergic system have been proposed as contributory factors in the development of Attention Deficit Hyperactivity Disorder (ADHD). Recently, we reported preferential transmission of a 148 bp allele of a highly polymorphic microsatellite marker located 18.5 kb from the 5′ end of the DRD5 dopamine receptor on chromosome 4 (Daly et al., 1999). We have now examined this (CA)n repeat with a new study sample consisting of 56 trios (mother, father and affected child) and 2 duos (either parent and affected child), diagnosed according to the DSM - IV criteria. As in our previous sample the microsatellite marker was found to have twelve alleles with the 148 bp allele being the most frequent at 45.7%. HHRR (Haplotype Based Haplotype Relative Risk) showed significant preferential transmission of the 148 bp allele (Chisquare = 4.11, P <0.05). These findings are supported by Tahir et al., (2000), and Barr et al., (2000). Thus, we have replicated our previous findings in a new sample derived from the same population and conclude that DNA variants at or near DRD5 confer risk for the development of ADHD.