Friday, 8 October 2010

ADHD, Genes, and Neurology

A Brain post, this one.

ADHD - Attention Deficit Hyperactivity Disorder. First, an explanation of what we know about it:

The excellent necroblog on the subject, ADHD and More, has a very good article on it.

British researchers compared the genomes of 366 white British children from 5 to 17 years old with attention deficit hyperactivity, or ADHD, to those of more than 1,000 similar children without the disorder. The scientists focused on a sequence of genes linked to brain development that has previously been connected to conditions like autism and schizophrenia.

In children without ADHD, about 7 percent of them had deleted or doubled chromosomes in the analyzed gene sequence. But among children with the disorder, researchers discovered about 14 percent had such genetic alterations. Scientists also found that 36 percent of children with learning disabilities in the study had the chromosomal abnormalities, compared to those with a normal IQ.

"This is the first time we've found that children with ADHD have chunks of DNA that are either duplicated or missing," said Anita Thapar, a professor at the MRC Centre in Neuropsychiatric Genetics and Genomics at Cardiff University who was one of the study's authors.
They got it factually wrong when the referred to "chromosomes" - we're talking about sequences of DNA, usually multiply-repeated ones, that we have good evidence are important in neurological development, not chromosomes as such. To use an analogy, like anomalies in the tread-pattern of a tyre, rather than a car with a missing or extra wheel.

As is typical, the effect is subtle. There is no "ADHD gene", just some sequences that make it more likely that a smaller-sized random hormonal glitch will cause real effects, rather than requiring a larger one - which happens sometimes too.
Peter Burbach, a professor of molecular neuroscience at University Medical Center Utrecht in the Netherlands, was surprised some of the genetic defects found for ADHD were identical to ones for autism and schizophrenia.
"This is not a structural abnormality in the brain, it's just the last phase of development that's gone wrong," he said. "It could be the brain just needs to be fine-tuned."
Perhaps. But I think not - we can certainly provide work-arounds and neural circuitry that will attenuate some of the worst effects, even convert them into advantages under some circumstances. But the basic structure will remain, even if asymptomatic due to deliberately induced anomalies in the more plastic parts of brain structure.

I don't think it's the last stage that's gone wrong. More like a very early one. Still, if we get a good result at the end by coarse-tuning of the plastic neurology during childhood, the effect is close to normal, and may be superior in some ways.

The corollary is that if the child is exposed to a malign environment when growing up, the symptoms of ADHD may be induced, even with a normal basic brain structure. Coarse-tuning the wrong way.

This may be a general rule (to a greater or lesser extent)in much neuro-atypicality.


Hedo said...

If the same/similar abnormalities exist between autism, ADHD and schizophrenia, that definitely serves to explain a good deal of my family's neurological history on both sides. My dad, brother and I all have ADHD, (though it's suspected that I might actually be on the Autism spectrum, beyond the overlap ADHD has) and my maternal aunt had schizophrenia. Seems like I was practically doomed/destined to end up with my layout! Haha.

Jennifer said...


Anonymous said...

Hence the absolute necessity for early childhood intervention if these young people are to have any chance later on in life. And the training needs to be continued all throughout life to maintain what has been achieved. Inactivity and lack of stimulation will turn these people into zombies later in life.