Chicago - July 16, 2009 - Japanese researchers have engineered mice that genetically mimic people with autism and they say studying these mice may help them discover what leads to the discorder.

"This is a mouse genetic-engineering feat," said Edwin Cook, an autism researcher from the University of Illinois at Chicago who was not involved in the study. The engineered mice have an extra copy of a chromosome that is believed to be associated with autism. The mice exhibit anxiety and poor social skills - traits commonly seen in autistic people.

Autism is difficult to study, particularly because it does not seem to be linked to one cause. Abnormal chromosomes - marked by partial extra copies or deletions of genetic data - are believed to account for 10 to 20 percent of autism cases. The most common mutation associated with autism is a partial extra copy of chromosome 15, an abnormality called chromosome 15q duplication syndrome, which occurs in 5 percent of autism cases.

Humans, like mice, have two copies of each chromosome - one each from the mother and the father. If an extra copy of chromosome 15 comes from the mother, the child has an 80 percent chance of developing autism, cook said. If the extra copy come from the father, the chance of developing autism is much lower. Scientists and doctocrs are not sure why.