Telegraph: Genetic link to autism may explain speaking problems

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Genetic link to autism may explain speaking problemsBy Highfield, Science Editor

Last Updated: 8:01am GMT 11/01/2008

A genetic link to autism has been found that may explain why affected children can take months or even years longer to speak.

Variants in this gene could help to diagnose the condition and, in the long run, provide valuable insights into how to develop more effective treatments.

Intriguingly the variants identified mostly affect boys, especially when inherited from mothers.

However, they are present in more than one third of the population, underlining how many genes contribute to the disorder and inheriting these gene variants does not mean that a boy will inevitably develop autism but will be more vulnerable to language-related problems.

The gene is most active in brain regions involved with thought and language, which suggests why affected children can have speech delayed, and the link with the developmental disorder is convincing because it has been confirmed by three teams of scientists.

The American Journal of Human Genetics publishes the findings of a team led by Prof Geschwind's team at the University of California, Los Angeles, along with one by Prof Aravinda Chakravarti and Prof Dan Arking from the s Hopkins University School of Medicine, Baltimore, and a team at Yale led by Prof State.

Confirmation by three groups, using different methods, suggests that several variants in the gene, called contactin-associated protein-like 2 (CNTNAP2), likely play a key role in the development of autism. The gene makes a protein that enables brain cells to communicate with each other through chemical signals and appears to play a role in brain cell development. "This gene not only may predispose children to autism," said Prof Geschwind, who searched for the gene in 500 affected families. "We think that it also may influence the development of brain structures involved in language, providing a tangible link between genes, the brain and behaviour."

The UCLA team examined CNTNAP2's presence in early brain tissue and discovered that the gene was most active in developing brain structures involved in language and thought, especially the frontal lobe. Statistical evidence for the gene was strongest in families with affected boys, who have three times the incidence compared with girls. "Finding genes is a first step in trying to better understand the disorder, and that many genes are likely to contribute," says Prof Geschwind, who is visiting the UK.

The Hopkins team studied almost 1,500 affected children and found that children with autism were about 20 percent more likely to have inherited the one gene variant from their mothers than from their fathers. "For males, individuals who get the version of the gene linked with autism from Mom have around 36% increase in risk relative to someone with no risk versions of the gene, and if the male child get the riskier version from both Mom and Dad, the risk increases by about 59%," Prof Arking says.

Prof Simon Baron-Cohen, a Cambridge University expert, comments: "CNTNAP2 is a very large gene that has already been associated with atypical brain development, including obsessive-compulsive disorder and epilepsy. The genetic variant identified in this study is a common variant in the general population, and may be more common in those who go on to develop autism. We will need further research to establish how big a risk this SNP contributes."

Around one per cent of the population is affected by autism but the causes remain complex and mysterious, with "autism spectrum disorders" ranging from severe retardation to milder versions such as Asperger syndrome, where sufferers are poor at reading emotions in others and understanding their motivation but can show impressive, albeit narrow, interests in anything from art to door knobs.

Because autism is a catch-all term for a wide range of symptoms - an inability to be social, such as eye contact and speech, and includes other symptoms, such as repetitive, obsessive behaviours - there is not going to be a single underlying cause, though earlier studies of twins underpin today's find that genes play a major role.

"Autism is highly heritable. Identifying the genes involved is crucial to our ability to map out the pathology of this isolating and sometimes terribly disabling disease, which currently has no cure," comments the director of the US National Institute of Mental Health, Dr Insel.

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