WASHINGTON — Close relatives of people with autism often have subtle differences in the way they move their eyes, researchers said on Monday in a finding that might help doctors better diagnose and treat the condition. The differences would not be noticeable in everyday life but they strongly suggest that many components of autism are inherited, the University of Illinois at Chicago team said. "What we hope these tests do is to identify subgroups of individuals or subgroups of families that have some sort of risk for autism," Matthew Mosconi, who worked on the study, said in a telephone interview. "The eye movement differences are the same as the ones that we saw previously in the kids with autism. It is a way to get at the functioning of these specific brain systems that we think are part of the development of autism." The tests Mosconi's team developed may also form the basis for treatment, and for predicting which patients might respond to specific treatments, he said. "The differences that we found are very subtle. These are not the kinds of differences in eye movements that you would ever detect during conversation with someone," Mosconi said. Autism is a complex and mysterious brain disorder usually diagnosed in early childhood. It is characterized by difficulties in social interaction and communication, ranging from mild to profound impairment. Autism spectrum disorders are diagnosed in one in 110 children in the United States and affect four times as many boys as girls. Researchers agree there is a strong genetic component. In June, the world's largest genetic scan of people with autism in their families found that many patients have their own unique pattern of genetic mutation, not necessarily inherited. Mosconi's team tested the inherited traits by enrolling 57 parents or siblings of people with autism and comparing test results to 40 people with no autistic relatives. "Family members reported more communication abnormalities and obsessive-compulsive behaviors than controls," Mosconi's team wrote in the Archives of General Psychiatry. The eye tests have been shown in other studies to reflect which brain pathways are involved in some of the characteristic patterns seen in people with autism. One test involved switching the gaze quickly to follow a light as it popped on and off, while another involved tracking a slow-moving object. "We know a good amount of what actually is going on in the brain while people are doing these very simple tests," Mosconi said. "We can identify specific parts of the brain that don't seem to be functioning at the optimal level," Mosconi said. The tests can help scientists identify the brain systems at work in autism, a very complex condition which varies from person to person, Mosconi said. They could also help in the search for specific treatments. Behavioral therapy can help some very young children with autism, studies have shown.