Autism gives up some genetic secrets


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At least 30% of cases of autism spectrum disorder are caused by genetic mutations that occur in a child, but do not occur in either parent, new research has found.

These "spontaneous" cases of autism are called de novo mutations. A research team analysed the genomes of more than 2500 families in which a single child but neither parent or siblings have autism spectrum disorder. It was carried out by Cold Spring Harbor Laboratory, Yale University, the University of California and the University of Washington, with the results published in Nature. The team says 30% is likely a conservative estimate because some types of mutations cannot be detected with current technology.

The study found that autism caused by de novo mutations generally divides into two risk classes - comparatively high IQ males who were also high functioning were in one group. The other group was made of low IQ males and nearly all affected females, who tend to have low IQ.

Recurrent de novo gene-disrupting mutations were found in 27 genes, which make them likely to be causal factors in the most severe cases - low IQ males and females.

Girls are believed to have a still unidentified factor which protects them against damaging mutations. When females are affected by autism it is often because genes that are highly active in early development experience devastating mutations.

The research involved exome sequencing - that is sequencing only the 2% of the full human genome that encodes proteins.

Previous exome studies of intellectual disability and schizophrenia have turned up sets of genes that overlap those identified in the autism study, the authors say.

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