Generalist genes 'cause all learning disabilities'

August 30, 2004

Learning disabilities result from general problems in the brain rather than

specific genetic or neurological defects,...

A large but unidentified group of genes, each with very small effects on

overall brain function, work together to determine most of mental ability,

says Plomin, at the Institute of Psychiatry in London.

If Plomin's theory proves correct, common learning disabilities such as

dyslexia will need a dramatic redefinition. Dyslexia is commonly defined as

a reading problem in someone who has otherwise normal intelligence.

In fact, Plomin disputes the idea of learning disabilities at all, saying

instead that these people simply fall at the lower end of the spectrum of

cognitive ability...

researchers also checked if a child with a problem in maths was likely to

have a twin with a reading disability, and vice versa. They found the link

was more common in identical than fraternal twins...

In fact, genes that affect reading have a 70 per cent chance of also

affecting maths ability. " Genes are generalists - the same genes affect all

disabilities, " concludes Plomin.

" People look for a hole in the brain that causes a problem, but I think the

brain evolved to work together to solve a problem, " he told New Scientist.

Any specific differences in learning ability are probably due to

environmental effects, he says.

At this point, the implications for children with learning problems,

specific or not, are unclear. Scientists do not know which genes, or even

how many genes, are involved. Some candidate genes may be those involved in

general brain processes such as synaptic plasticity, Plomin says.

Furthermore, the individual effect of each gene involves is likely to be so

small - accounting for less than one per cent of the variation in general

cognitive ability - that studies attempting to find them will have to

analyse huge numbers of people.

Singer, Salford

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