"These findings confirm the role of genetics in autism and are a major step in narrowing the search for the specific genes involved," said Duane Alexander, M.D., Director of the National Institute of Child Health and Human Development (NICHD) and co-chair of NIH's Autism Coordinating Committee.

At least one in 500 people are affected by some form of autism, a neurodevelopmental disorder that causes problems with communication and social interaction, as well as repetitive actions and interests. Earlier studies with families and twins have shown that there is likely to be a strong inherited component to autism. Because of the wide range of patients' symptoms, many researchers suspect the disorder is the result of a complex interaction between several different genes involved with brain signaling and development. Unidentified environmental factors are also likely to play a role.

In this study, researchers screened the DNA of more than 150 pairs of siblings with autism. They found extremely strong evidence that two regions on chromosomes 2 and 7 contain genes that are involved with autism. Likely locations for autism-related genes were also found on chromosomes 16 and 17, although the strength of the correlation was somewhat weaker. The findings will appear in the September issue of the "American Journal of Human Genetics."

Chromosome 7 is known to be associated with many language disorders and has been shown to be linked with autism in some earlier studies, but not all.

"Because of the size of this study and the strength of the correlation found, there is now little doubt that the so- called language disorder chromosome is significantly involved with the development of autism," said Marie Bristol-Power, Ph.D., NICHD Special Assistant for Autism.

Researchers were particularly excited by evidence of an autism link on chromosome 2, since this area had recently been identified by another, independent research group. NICHD is currently supporting a range of research looking at the interaction between the genes for early brain development located on chromosome 2 and environmental influences.

"We wouldn't be looking for genes on chromosome 2 if not for these findings. Now we can be fairly certain that genes on chromosomes 2 and 7 are linked with autism," said Dr. Ed Cook from the University of Chicago, a participating researcher on the project.

Dr. Bristol-Power noted that the project's international scope was critical in getting a sufficiently large number of patients who were diagnosed using the same methods. Drawing DNA from a large number of people allows researchers to make more definitive claims of linkage between the DNA region and the disease.

"Teams from all over the world worked together to produce this result," said Dr. Bristol-Power. "This kind of collaboration is how the problem of autism will eventually get solved. Even larger numbers, 400-500 pairs of relatives, are needed to get more definitive answers, and collaborative international efforts to complete a genome scan on such numbers are now underway."

This work was carried out by members of the International Molecular Genetic Study of Autism Consortium, a group of clinicians and scientists from the UK, USA, France, the Netherlands, Denmark, Italy, and Greece. (For more information, see website http://www.well.ox.ac.uk/~maestrin.iat.html.) The US component of their work was conducted as a part of the Yale/University of Chicago/UCLA Collaborative Program of Excellence in Autism (CPEA), part of the Network on the Neurobiology and Genetics of Autism, a research initiative funded by NICHD and the National Institute on Deafness and Other Communication Disorders.

"It is encouraging to know that so many investigators in the consortium are working together for so many years to accomplish the goals of adding to our understanding of the causes of autism," said Dr. Cook. "It is even more encouraging to know how many outstanding investigators in other research groups, including other members of the CPEA, are now focusing their talents on this often devastating illness. Most importantly, none of this would be moving forward without the outstanding participation of families of individuals with autism."

Researchers currently know little about what is going wrong in the brains of autistic children, and they hope to gain answers by locating the specific genes involved and understanding their functions.

"We will continue to search for the individual genes which are linked with the development of autism," said Dr. Fred Volkmar of the Yale Child Study Center. "Knowledge of the genes will lead us to better, earlier diagnoses and interventions and, ultimately, better treatment options."

This work has been funded by the U.K. Medical Research Council, The Wellcome Trust, BIOMED 2 (grant CT-97-2759), EC Fifth Framework (grant QLG2-CT-1999-0094), Telethon- Italy (grant E.1007), the Janus Korczak Foundation, Deutsche Forschungsgemeinschaft, Fondation France Télécom, Conseil Régional Midi-Pyrénées, Danish Medical Research Council, Sofiefonden, the Beatrice Surovell Haskells Fund for Child Mental Health Research of Copenhagen, the Danish Natural Science Research Council (grant 9802210), the National Institute of Child Health and Development (grant 5-P01-HD-35482), and two other NIH Institutes, the National Institute of Mental Health (grants NIH K05 MH01196 and K02 MH01389) and the National Center for Research Resources (grant MO1 RR06022 GCRC NIH).