MONDAY, Aug. 2 (HealthDay News) -- In another sign that autism is at least partly inherited, a new study reveals that close relatives of people with the disorder share something in common: their eyes are much more likely than those of other people to function abnormally.
"There are brain abnormalities that run in families with autism," said study co-author John A. Sweeney. "These findings might be telling us that there's an important genetic contribution to autism."
The causes of autism, which affects an estimated one in 110 children in the United States, are unclear, according to the U.S. Centers for Disease Control and Prevention. The number of children diagnosed with the disorder has risen in recent years, but it's not clear if that's largely due to more awareness or some other factor, such as something in the environment around these children.
Previous research has suggested that family members of autism patients are more likely to have some minor brain impairments than other people, said Geraldine Dawson, chief science officer of Autism Speaks, an advocacy organization.
In the new study, researchers looked for signs of eye abnormalities that are common in people with autism. They often have difficulty tracking moving objects in the first milliseconds that they look at those objects, explained Sweeney, director of the Center for Cognitive Medicine at the University of Illinois at Chicago.
The abnormalities are minor and probably have no significant impact on vision, Sweeney said. "These parents are walking around fine, and it's unlikely that these [abnormalities] are going to affect anyone's life."
Still, the vision abnormality suggests that something has gone awry in the brain.
Sweeney and colleagues studied the eye movements of 57 close relatives -- 42 parents and 15 siblings of people with autism. They compared them to 40 other people who were similar to them in age, gender and IQ but weren't close relatives of people with autism.
More than 50 percent of the family members of people with autism showed different signs of abnormal eye movements, Sweeney said. In the general population, about 5 percent of people might have the abnormalities, he added.
Essentially, the study suggests relatives of people with autism share an abnormality in the brain that, for them, didn't fully develop into autism.
Sweeney acknowledged that the study doesn't shed light on exactly how responsible genetics are for autism. Still, the findings fit in with research "that suggests the problems in autism are much more the results of genetic than environmental factors," he said.
The study also provides evidence that the genes thought to carry the risk for autism specifically affect parts of the brain such as the cerebellum and frontal cortex, Dawson said.
The study findings are published in the August issue of the Archives of General Psychiatry.
For more on autism, try the U.S. National Institute of Neurological Disorders and Stroke.