Different genetic influences cause cognitive impairments in ADHD
09 November 2010
New research from the Institute of Psychiatry at King’s, suggests that cognitive impairments seen in patients with attention-deficit/hyperactivity disorder (ADHD) are caused by different genetic or familial influences. These findings could help geneticists home in on the genes causing ADHD and pave the way for the development of new treatments.
Patients with ADHD have widespread cognitive impairments, but it has not been clear whether these problems share a single underlying cause or result from several independent pathways.
Dr Jonna Kuntsi and colleagues studied a large sample of ADHD and control sibling pairs including 464 patients with ADHD, 456 of their siblings, and 345 controls, who carried out a series of computer-based tasks measuring different cognitive variables. The variables which showed the highest phenotypic correlation with ADHD were mean reaction time, variability in reaction times and omission and commission errors (the failure to respond to a signal and the failure to inhibit a response, respectively).
The results revealed two separate familial factors influencing ADHD, with the larger of the two (reaction time) reflecting 85% of the familial variance of ADHD, and the smaller factor (omission and commission errors) reflecting 13%.
While sibling studies are not able to distinguish between genetic influences and shared environmental influences, the results of previous twin studies suggest that the familial influences seen here are largely genetic.
The distinction between these two familial factors is consistent with recent theoretical models of two separable underlying neurobiological processes in ADHD, where the first process reflects a vigilance decrement, that is, patients becoming less vigilant over time during the tasks, and the second process reflects executive control on sustaining attention and inhibiting inappropriate responses during the tasks.
Dr Kuntsi said: 'The evidence from our study together with earlier findings raise the possibility that there is one set of familial influences on the core, stable impairment in ADHD and a second set of familial influences on cognitive impairments that relate to developmental executive function processes. If so, we may need to develop interventions that target specific stages of development and aspects of cognitive impairments in ADHD.'
The researchers are now in the process of conducting a follow-up study on the local sample of ADHD and control sibling pairs from this study. In the new study, the researchers will be able to measure participants’ brain processes directly using electrophysiology while they complete the cognitive tasks. The brain processes of patients whose condition has improved since the original study can then be compared with those who still have ADHD.
'The follow-up study enables us to directly address the developmental questions – why do some children with ADHD seem to grow out of their disorder while others do not,' said Dr Kuntsi.
The paper is published in the Archives of General Psychiatry: Kuntsi, J. et al. 'Separation of cognitive impairments in attention deficit/hyperactivity disorder into two familial factors'. Vol. 67 No. 11 pp. 1159-1167. November 2010.
The follow-up study is ongoing. Information can be found here:http://www.action.org.uk/our_research/attention_deficit_hyperactivity_disorder_adhd_why_do_some_children_grow_out_their