It has long been suspected that errors in a person's genetic blueprint may play a part in autism, and two such anomalies have now been found by researchers involved in the international Autism Genome Project.

During the last five years, this collaborative project has involved 120 scientists from 19 countries and 50 institutions in comparing the genomes of 1,200 families with multiple cases of autism - the largest survey of its kind ever conducted.

The work, described in Nature Genetics, implicates a region of chromosome 11 and a specific gene, located on chromosome 2, called neurexin 1. The latter belongs to a family of genes that help nerve cells communicate and which may have a critical role in autism spectrum disorders.

It is thought that there may be as many as six major genes involved in autism, and perhaps a further 30 that may confer a lesser degree of risk. A combination of mutations in any of these genes could increase the chance of being born with autism.

Although it will be some time yet before scientists have a more complete understanding of the genetics of autism, this latest discovery is a major step forward and it offers hope that a genetic test for autism, as well as more effective treatments, will eventually be developed.

Meanwhile, the project's work is continuing and the next phase, which will take three years and cost more than £7m, will focus in ever more detail on the suspect genes.

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First published in 2004

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