Scientists have found the first substantial evidence that autism may be caused by genetic differences that damage the connections in the brain in early childhood.
Three studies have identified genetic variations which may help explain the origins of the condition, including one that could account for as many as 15% of autism cases.
The researchers believe the findings could help the process of identifying people with an autistic spectrum disorder, improve medical treatments, and potentially lead to diagnostic tests for the condition. About 500,000 people in Britain are autistic, including some 133,500 children, according to the National Autistic Society (NAS), which campaigns on their behalf.
People with autism have difficulty relating to those around them and often have higher than usual rates of mental illness, unemployment and social exclusion.
Two papers published online in Nature, by Hakon Hakonarson and colleagues at the Centre for Applied Genomics at the Children’s Hospital of Philadelphia, show that mutations in genes that play a role in establishing connections within a child’s brain increase his or her chances of developing autism. While a single genetic variant may pose a small increased risk for a child, the researchers claim to have identified variants that may explain up to 15% of the prevalence of autism.
Philip Johnson, the hospital’s chief scientific officer, likened the significance of the findings to previous breakthroughs in knowledge about the links between genetics and cancer. “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,” he said. “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.”
The third paper, published in Molecular Psychiatry, sets out research among those with autism and their families work by a team led by Professor Tony Monaco, of the Wellcome Trust Centre for Human Genetics at Oxford University. It also shows that genes involved in the growth and development of nerve cells in the brain could increase someone’s susceptibility to autism. “This does seem to fit with what we know from brain scans – that people with autism may show different or reduced connectivity between different parts of the brain,” said Monaco.
However, Richard Mills, research director of the charity Research Autism, cautioned that the research did not answer many key questions. “People shouldn’t get too excited about thinking that this research identifies a gene for autism. These studies add to the overall picture of how genes interact with each other and how they influence connections within the brain, but it’s not groundbreaking in terms of telling us which genes are implicated and their interaction with the overall environment.”
The NAS welcomed the new research. A spokeswoman said: “There is evidence to suggest that genetic factors are responsible for some forms of autism. However, the difficulty of establishing gene involvement is compounded by the interaction of genes with environmental factors. Various studies over many years have sought to identify candidate genes, but so far inconclusively.”
The exact causes of autism are still unknown, and many experts believe the type of behaviour that leads to people being diagnosed with autism may have more than one cause, she added. Other theories advanced in recent years as potential contributory factors include drinking during pregnancy, older fathers and early television viewing, though none has been substantiated.
The government today starts a 20-week consultation into how support and services for people with autism can be improved in areas such as health, employment and training.
The Office of National Statistics research shows that about 90 in 10,000 children have an autistic spectrum disorder. No study has been undertaken into the prevalence of autism among adults.