A study of around 1,000 Australian and Dutch adolescents has pinpointed specific areas of DNA which may explain wide variations in intelligence

Janelle Miles:

Scientists carried out IQ tests and took blood samples from non-identical twins and siblings for the research, published this week in the American Journal of Human Genetics.

They identified locations on chromosomes 2 and 6 which they suspect contain genes regulating aspects of intelligence.

"The aim now is to try and look in those chromosome regions and find out which particular genes are driving this and then to find out what the variations within those genes are that are responsible for differences in intelligence," Brisbane-based geneticist Nick Martin said.

"It's possible that there are some genes that are only involved in intellectual disability and others responsible for high IQ, but my guess is that it'll probably be variations of the same genes."

Scientists believe between 40 and 80 per cent of variation in human intelligence is attributable to genetic factors.

Professor Martin, of the Queensland Institute of Medical Research (QIMR), and colleagues found where the twins and other sibling pairs had significant differences in IQ, they also had big variations in the identified regions of chromosomes 2 and 6.

Identifying responsible genes could help in the development of improved treatment for disorders like dyslexia and autism.

"My basic rule of life is if you want to fix something, you first find out what's going wrong," Prof Martin said.

"If you find out what the fundamental problem is, it may give us clues for new therapies which could possibly be pharmaceuticals or maybe even dietary therapy.

"But that's the long-term goal."

The region identified on chromosome 2 overlaps with an area that's been associated with autism and the targeted section of chromosome 6 has been implicated in reading disability and dyslexia, the researchers said.

Previously, the identification of genes underlying variations in human intelligence has been limited to neurological mutations which have severe cognitive effects such as in Pick's disease, a form of dementia occurring in middle age.

"Identifying genes for variation in the range of normal intelligence could provide important clues to the underlying mechanisms of milder but more-prevalent forms of impaired cognitive functioning, which are often associated with autism, schizophrenia, reading disorders and attention deficit disorder," the researchers said in the journal article.

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