CHICAGO Three U.S. teams of scientists using different research approaches said on Thursday that different flaws in a single gene raise the risk of autism.
It is the second study published this week to find new genetic causes of autism, a complex and poorly understood set of disorders.
"We hope this means that this gene really does influence risk and that is why different labs all landed on it at the same time," said Dr. Matthew State of Yale University.
Two of the studies pointed to a genetic variation in the gene that is found commonly, and a third found a rare mutation of this same gene. All appear to be inherited.
"This convergence of rare and common variants in autism is unusual but reinforces the growing consensus among genetics researchers that both types of changes in DNA sequence are going to be important contributors," State said in an e-mail.
Autism includes a range of disorders, from the mild Asperger's syndrome to profound mental retardation and lack of ability to socialize. It affects as many as 1 in 150 children in the United States -- up to 1.5 million children and adults.
The three studies, published in the American Journal of Human Genetics, all point to contactin associated protein-Like 2 or CNTNAP2 -- a gene that makes a protein that allows brain cells to communicate.
Because speech delays are a hallmark of autism, researchers at the University of California, Los Angeles, studied the age when a child first speaks. A prior study of families with autistic children linked a specific region of chromosome 7 to autism.
The researchers scoured every gene in this region using DNA samples from 172 families. Four promising genes, including CNTNAP2, turned up. They cross-checked their findings on a new group of 304 families and the CNTNAP2 gene turned up consistently.
The findings not only point to the CNTNAP2 gene, but suggest the gene is important for language development.
"The fact that we found CNTNAP2 concentrated in the brain's structures that are involved in higher cognition gives us strong clues about how its disruption might adversely shape brain development, including speech and language," UCLA's Brett Abrahams said in a statement.
Researchers at Johns Hopkins University and the University of Illinois at Chicago used genome-wide screening techniques on families that had two or more children with autism.
They found that a single change in CNTNAP2 made children vulnerable to developing autism.
"It clearly suggests there is this very common factor that plays a role in autism," said Aravinda Chakravarti of Johns Hopkins University School of Medicine.
For the Yale study, State started with a patient with autism who had a rare chromosomal abnormality that disrupted CNTNAP2.
He looked at the entire DNA code of the gene in 635 people with autism as well as 942 healthy volunteers and found multiple rare changes in the sequence of CNTNAP2 in patients with autism, including one change in three families with autism that was not found in 4,010 chromosomes from healthy people.
State said researchers now need to gain a better understanding of the gene's role in normal brain development, and how genetic changes alter this process.
On Wednesday a team of researchers found a stretch of DNA on chromosome 16 that they said may cause 1 percent of autism cases.
(Editing by Maggie Fox and Mohammad Zargham)