Researchers have made an important discovery in the search for answers to the mystery of autism, according to a large study in U.S. quoted by media reports on Thursday.

They found that a rare genetic variation dramatically raises the risk of developing autism. In fact, kids with the genetic flaw have a 100-fold increased chance of developing autism than kids without it.

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."

The researchers found that a segment of chromosome 16 is either missing or duplicated in about one percent of individuals with autism or related disorders.

"We've provided very compelling evidence that this particular small stretch of the genome provides an important clue to the biological roots of autism," Dr. Mark Daly said.

When the biological pathways involved are figured out, scientists can try to design drugs to target chemicals in the brain to treat autism.

Autism, a complex, poorly understood disorder, is characterized by repetitive behaviors and poor social interaction and communication skills. The research has mainly centered on genetic causes, and on whether it could be caused by the mercury-based preservative once used in childhood vaccines, which has been repeatedly discounted.

The number of children diagnosed with autism has risen in recent years to as many as one in 150 American children, but experts are unsure whether its prevalence really is increasing or the trend is due to a broader definition of autism.

(Agencies via Xinhua News Agency January 11, 2008)