Direct Genetic Links to ADHD Identified

Article excerpt

Attention-deficit/hyperactivity disorder is a neurodevelopmental 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, published online, provide the first direct evidence of a genetic basis for ADHD, Dr. Nigel Williams of Cardiff University, Wales, and his colleagues reported (Lancet 2010 [doi: 10.1016/S0140-6736(10)61109-9]).

The investigators performed a genome-wide analysis of large, rare chromosomal deletions and duplications known as copy number variants (CNVs) in 366 children with ADHD and 1,047 controls. The genome-wide burden of CNVs was significantly greater in the ADHD patients, compared with that 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 significantly enriched for loci that have previously been implicated in those disorders - with particular overlap at a region on chromosome 16 that spans numerous genes, including one that affects brain development.

Furthermore, although the rate of CNVs was significantly 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 (rates of 0.424 and 0.075, respectively).

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 a result of bad parenting or other external factors, coauthor Dr. Anita Thapar said during a press conference on the findings. …