Association of high reaction time variability with the 7-repeat allele absence appears to be the most consistent result and seems to be specific to ADHD .
Speed of processing , set-shifting and cognitive impulsiveness were less frequently investigated but seem to be altered in the 7-repeat allele carriers .
High reaction time variability seems to be the most replicated cognitive marker associated with the 10-repeat homozygosity .
BACKGROUND We review ed systematic ally the results of genetic studies investigating associations between putative susceptibility genes for attention-deficit hyperactivity disorder ( ADHD ) and neuropsychological traits relevant for this disorder .
A Pilot Twin Study of Psychological Measures of Attention Deficit Hyperactivity Disorder
There has been much interest in the genetics of attention deficit hyperactivity disorder and molecular genetic studies are now underway . The success of genetic studies will depend on how well the phenotype is defined . Twin studies using parent and teacher rated question naires or interviews all appear to yield highly heritable measures . Nevertheless , there is evidence to suggest that parent measures are subject to rater bias . Consequently there has been much interest in obtaining more objective measures of related traits such as attention span and impulsiveness using , computerised neuropsychological tasks . However there have been few twin studies examining the genetic contribution to these neuropsychological measures . The present study aims to investigate whether performance on the  Matching Familiar Figures Test ( MFFT ) and Continuous Performance Task ( CPT )  is genetically influenced in childhood . 20 monozygotic ( MZ ) and 20 dizygotic ( DZ ) twin pairs were r and omly selected from the Greater Manchester Twin Register . Preliminary data suggest that MZ twins perform more similarly than DZ twins on the MFFT , but not the CPT . Future work needs to examine whether other neuropsychological measures commonly used in research on ADHD are genetically influenced using larger twin sample
Association of high reaction time variability with the 7-repeat allele absence appears to be the most consistent result and seems to be specific to ADHD .
Speed of processing , set-shifting and cognitive impulsiveness were less frequently investigated but seem to be altered in the 7-repeat allele carriers .
High reaction time variability seems to be the most replicated cognitive marker associated with the 10-repeat homozygosity .
BACKGROUND We review ed systematic ally the results of genetic studies investigating associations between putative susceptibility genes for attention-deficit hyperactivity disorder ( ADHD ) and neuropsychological traits relevant for this disorder .