Azara Blog: ADHD allegedly has a genetic link

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Date published: 2010/09/30

The BBC says:

The first direct evidence of a genetic link to attention-deficit hyperactivity disorder has been found, a study says.

Scientists from Cardiff University, writing in The Lancet, said the disorder was a brain problem like autism - not due to bad parenting.

They analysed stretches of DNA from 366 children who had been diagnosed with the disorder.

But other experts agued ADHD was caused by a mixture of genetic and environmental factors.

At least 2% of children in the UK are thought to have attention-deficit hyperactivity disorder (ADHD).

Affected children are restless and impulsive. They may also have destructive tendencies, and experience serious problems at school and within family life.

The researchers compared genetic samples from ADHD children, with DNA from 1,047 people without the condition.

They found that 15% of the ADHD group had large and rare variations in their DNA - compared with 7% in the control group.

Professor Anita Thapar said: "We found that, compared with the control group, the children with ADHD have a much higher rate of chunks of DNA that are either duplicated or missing.

"This is really exciting - because it gives us the first direct genetic link to ADHD.

"We have looked at lots of potential risk factors in the environment - such as parenting or what happens before birth - but there isn't the evidence to say they're linked to ADHD.

"There's a lot of public misunderstanding about ADHD. Some people say it's not a real disorder, or that it's the result of bad parenting. "Finding this direct link should address the issue of stigma."
[Oliver James, a clinical child psychologist and broadcaster] said: "Only 57 out of the 366 children with ADHD had the genetic variant supposed to be a cause of the illness.

"That would suggest that other factors are the main cause in the vast majority of cases.

"Genes hardly explain at all why some kids have ADHD and not others."

It is unbelievable how much press coverage this study generated. Unfortunately the Cardiff researchers seem to be desperate to prove that ADHD has a genetic cause, and that is not a good start. And, as Oliver James and others have mentioned, the numbers quoted by the researchers are so weak that their headline posturing does not really stand up to scrutiny. For example, the probability that you have ADHD given that you have these "large and rare variations" in your DNA is 15% x 2% / (15% x 2% + 7% x 98%) = 4.2%, and so the probability that you do not have ADHD given that you have these "large and rare variations" in your DNA is 95.8%. Thus if you have these "large and rare variations" then you are 95.8/4.2 = 23 times as likely not to have ADHD as to have ADHD. This is not a particularly useful predictor of having ADHD.

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