When this study appeared last year, many media sources reported it as evidence that scientists had found “the ADHD gene”. There are two problems with this interpretation. Firstly, only a small proportion of patients carried “large rare” CNV. 85% did not carry any, although more detailed future studies, able to detect smaller CNVs, might have found more (the smaller they are, the harder they are to detect.)
The deeper problem is that there wasn’t just one CNV. In fact, there were dozens of different large deletions or duplications in the ADHD group. This is similar to the results of other CNV studies.
Furthermore, even when the same CNV turns up repeatedly in many independent patients, these patients very often have different diseases. Many of the leading risk CNVs for autism, say, have also been found in ADHD and schizophrenia, epilepsy, or intellectual disability – and vice versa.
To take just one example, the “15q13.3” deletion, so called because it affects a particular part of Chromosome 15, has been found in people with schizophrenia, epilepsy, autism, and possibly even antisocial behaviors.
So although scientists set out trying to discover the genetic causes of named psychiatric disorders like “autism” and “schizophrenia,” they’re increasingly finding that these diagnoses don’t correspond to particular genes at all.
Instead, it may be that these diagnostic categories are just describing particular symptoms of certain genetic disorders. So, rather than saying that 15q13.3 deletion causes schizophrenia, for example, in the future we might say that some of the features of schizophrenia are amongst the effects of the 15q13.3-deletion-syndrome.
It’s only early days yet, but as this research advances further, and as technology allows ever-smaller CNVs to be picked up, these kinds of genetic findings may present a serious challenge for existing psychiatric diagnostic systems.
Are you a scientist? And have you recently read a peer-reviewed paper that you would like to write about? Please send suggestions to Mind Matters editor Gareth Cook, a Pulitzer prize-winning journalist at the Boston Globe. He can be reached at garethideas AT gmail.com or Twitter @garethideas.