Scientists have made a breakthrough in the fight against autism, by identifying a genetic defect that appears to increase one's susceptibility to the condition.
The multi-institutional study involving Massachusetts General Hospital (MGH), found that a segment of chromosome 16 is either missing or duplicated in about one per cent of individuals with autism or related disorders.
The study's senior author, Dr. Mark Daly, of the Massachusetts General Hospital Center for Human Genetic Research, said that those people who have this chromosomal abnormality have "a very, very high risk of autism."
"While epidemiologic studies indicate a very large genetic component to autism, little is known about how specific genes are involved. We're still a long way from understanding how this chromosomal deletion or duplication increases the risk for autism, but this is a critical first step toward that knowledge," Dr. Daly said.
Moreover, the researchers found that the gene flaw does not appear to be inherited, as none of the parents of autistic kids with the flaw didn't have the defect.
Studies suggest that up to 90 per cent of cases of autism spectrum disorders have some genetic component, but only 10 per cent of cases can be attributed to known genetic and chromosomal syndromes.
Dr. Daly 's team decided to conduct a complete genome scan of samples from the Autism Genome Research Exchange, which contains DNA from families in which at least one child has autism or a related disorder.
The scan of more than 1,400 autistic children and a similar number of their unaffected parents revealed that an identical region of chromosome 16 was deleted in five of the kids with an autism spectrum disorder.
They then looked at clinical testing data from almost 1,000 patients from Children's Hospital Boston - about half of whom had been diagnosed with autism or a related developmental delay.
Among those with a developmental disorder, five children had the same deletion, and four more had a duplicated chromosome segment. No abnormalities were seen in DNA from children without autism or developmental delay.
Confirmatory data was also obtained by colleagues from deCODE Genetics of Iceland, who found the same deletion in 3 of almost 300 individuals with an autism spectrum disorder and also in a few with other psychiatric or language disorders. Among almost 20,000 members of the deCODE database who had not been evaluated for language or psychiatric disorders, the deletion was seen in only 2 individuals.
Results from the deCODE scan indicate that, while this chromosomal deletion occurs in only .01 percent of the general population, it is 100 times more prevalent in those with autism spectrum disorders.
"These large, non-inherited chromosomal deletions are extremely rare, so finding precisely the same deletion in such a significant proportion of patients suggests that it is a very strong risk factor for autism. We're now pursuing more detailed genetic studies to figure out which genes in this region are responsible for this effect in order to gain a better understanding of the underlying biology and potential clues to therapeutic approaches," Dr. Daly said.
He added that his team is now pursuing more detailed genetic studies to see if other genetic flaws can be found.
The findings could have important significance for improving diagnostic methods, Dr. Daly concluded.
The study is published in the New England Journal of Medicine.