Study yields evidence of genetic basis for ADHD

Attention-deficit/hyperactivity disorder is a neurodevelopment disorder, rather than a purely social construct according to British researchers who have found that a type of genetic variation associated with brain disorders such as schizophrenia and autism also occurs in excess in ADHD patients.

The findings provider the first direct evidence of a genetic basis for ADHD was reported.

They performed a genomewide analysis of large, rare chromosal deletions and duplications known as copy number variants (CNVs) in 366 children with ADHD and 1,047 controls.  The genomewide burden of CNVs was significantly greater in the ADHD patients than in the controls — rates of 0.156 and 0.075, respectively, they found.

The CNVs identified in this study are similar to those found in patients with schizophrenia and autism, and are enriched for loci that have previously been implicated in those disorders — with particular overlap at a region on chromosome 16 that spans a number of genes, including one that affects brain development.

Furthermore, although the rate of CNVs was significant higher in children with ADHD with and without intellectual disability, compared with the general population, the rate was particularly high in those with intellectual disability, defined as those with an IQ of less than 70.

The findings are noteworthy because despite evidence that ADHD might be a genetic condition — for example, it has an estimated heritability of 76% — there has been a great deal of debate over whether it is result of bad parenting or other external factors.

ADHD can be stigmatizing and finding this direct genetic link to ADHD should help clear this misunderstanding and address this issue of stigma. This will be the start of a much more scientific venture because our findings are going to help us unravel the biologic basis of ADHD.

The subjects were recruited from community clinics and had met diagnostic criteria for ADHD or hyperkinetic disorder. They were aged 5-17 years (mean, 10.5 years), were of white U.K. origin and had a mean IQ of 86. Controls were unrelated, ethnically matched children from the 1958 British Birth Cohort.

Our results emphasize that further investigation of CNVs in ADHD is a priority for research into this disorder. Also, the finding that more than a third of ADHD children with intellectual disability carried a large, rare CNV — and the fact that none of these children had not been assessed for this type of mutation by clinical services — suggests that routine referral to clinical geneticists and screening for such mutations could be helpful for children with ADHD who also have intellectual disability.