Common genetic variations that can contribute to autism have been reliably identified for the first time in research that promises to improve the diagnosis and understanding of the disorder.

The DNA changes, which affect genes involved in early brain development, are together involved in up to 15 per cent of autism cases, the most extensive study of its kind yet conducted has found.

The findings significantly deepen scientific understanding of the genetic origins of autism, offering insights into the condition’s underlying biology that could eventually lead to new treatments.

While it has long been established that autism has a strong inherited component, previous research has failed to reveal any common DNA variants that were involved.

The new study has found a robust link between autism and six such variants. These do not invariably cause the condition, but they are about 20 per cent more common in children with autism than they are in those who are unaffected.

The results are especially significant because the variants lie between two genes, called CDH9 and CDH10, which are known to play an important role in forming nerve connections in the brain.

Hakon Hakonarson, of the Children’s Hospital of Philadelphia in the United States, who led the research, said: “Because other autism researchers have made intriguing suggestions that autism arises from abnormal connections among brain cells during early development, it is very compelling to find evidence that mutations in genes involved in brain interconnections increase a child’s risk of autism.”

Philip Johnson, the hospital’s chief scientific officer, said: “This comprehensive research opens the door to more focused investigations into the causes of autism disorders. It moves the field of autism research significantly ahead, similar to the way oncology research progressed a few decades ago with the discovery of specific genes that give rise to cancers.

“Our extensive paediatric genomics programme has pinpointed particular genes and biological pathways, and this discovery provides a starting point for translating biological knowledge into future autism treatments.”

In the study, which is published in the journal Nature, the research team compared the DNA of 3,100 individuals from 780 American families each with at least two autistic children. The scan was then repeated in a group of 1,200 people with autism and nearly 6,500 unaffected controls.

This revealed six genetic variants that were significantly more common in the autistic group. All were on chromosome five, and appear to affect the CDH9 and CDH10 genes.

Daniel Geschwind, of the University of California Los Angeles, another member of the study team, said that while these genetic variants do not directly cause autism, their presence appears to increase the risk of developing it.

“While this gene variant is common in the general population, we discovered that it occurs about 20 per cent more often in children with autism,” he said. “A major change like this in the genetic code is too common to be a simple mutation: it is a risk factor in the origin of the disease.

“This is a landmark finding. It’s no coincidence that a gene linked to autism has a higher concentration in key brain regions that regulate speech and the ability to interpret social interaction. Our research suggests that CDH10 is switched on at a very early stage and plays an important role in regulating the developing brain. This prenatal activity somehow makes the infant more susceptible to autism.”

The CDH9 and CDH10 genes affect the way that nerve cells in the brain communicate with one another, which is thought to be a problem in autistic spectrum disorders (ASD).

“These molecules are expressed on the cell surfaces of neurons, and they are involved with shaping both the physical structure of the developing brain and the functional connections among different brain regions,” Dr Hakonarson said.

“Although a particular gene variant may contribute a small risk for an ASD in a particular individual, we estimate that the variants we discovered may contribute to as many as 15 per cent of ASD cases in a population.”

Autism involves a characteristic triad of symptoms: impairments in social and communication skills, as well as repetitive behaviour and/or narrowly restricted interests. It is estimated that as many as one in 150 people have a disorder on the autistic spectrum.

Previous research has identified rare genetic variations that are involved in the condition, particularly of a type known as copy number variants in which entire stretches of DNA are duplicated, deleted or rearranged.

The new research provides by far the strongest indication yet that common genetic changes are also implicated in the disorder.

A second study led by Dr Hakonarson has found evidence of several copy number variants that are linked to autism. One of these affects a similar molecular pathway to the one that appears to be impaired by the common variations.

Professor Simon Baron-Cohen, of the University of Cambridge, welcomed the new reseach. He said: “The challenge for future research will be to establish which of these findings can be well-replicated in independent samples and by independent labs; what the functions of these genes are and where they are expressed; which aspects of the phenotype of autism they can explain; whether they relate to one subgroup or the whole autism spectrum; how many of these genes are necessary and sufficient to cause autism; and how they may interact with environmental factors.

“The puzzle is slowly being pieced together, and the science of autism is accelerating in promising ways.”

— Five people with autism spectrum disorders will meet Phil Hope, the Care Services Minister, today to respond in person to a public consultation on the Government’s national autism strategy. The consultation, which launches today, will run for 20 weeks and seeks views from people with autism, their carers, their families and service providers.

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