IN THEIR EYES: Some autistic individuals have eye-movement deficits, and a new study shows that a similar pattern can be found in some of their close relations--even those who don't have other signs of the disorder. Image: WIKIMEDIA COMMONS/FRANZISKA F
The tangled web of autism symptoms and genetic markers has left researchers searching for patterns and trends in unusual places. New work examining the subtle symptoms shared by close relatives has underscored the disease's heritability. Findings published online August 2 in Archives of General Psychiatry add to the growing list of familial clues about the disease: shared eye-movement deficits.
Researchers working at the University of Illinois at Chicago's (U.I.C.) Center for Cognitive Medicine have found a striking trend: those with autistic relatives are more likely to show disrupted eye movement similar to their afflicted relation.
Large-scale genetic studies have turned up nuanced and conflicting results about the genetic basis of autism and its myriad symptoms. Other research has discovered that many people with an autistic relative or child might themselves have some subtle behavior variant as well, such as obsessive-compulsive tendencies or communication problems.
Eye movement is easier to study neurologically than complex social and behavioral patterns—in large part because "we know a lot about what parts of the brain are involved," says Matthew Mosconi, an assistant professor of psychiatry at the U.I.C. and lead author of the new study. And the new findings examine basic deficits unclouded by social tendencies, such as the aversion many people with autism spectrum disorder have to looking at faces.
To monitor test subjects' eye movements, fluidity and response time, the researchers used exacting projection and recording equipment. They tested 57 people (ages eight to 54) with immediate family members who had autism and 40 volunteers who did not have a family history of mental disorder. None of the subjects were themselves autistic or had other developmental disorders.
Subjects were tested for their rapid eye movement that allows focus to shift on multiple objects in the field of vision (aka saccade) and ability to follow objects moving across the visual field, known as smooth-pursuit.
Although not everyone with autism exhibits eye-movement deficits—and not everyone has both of the types studied—those who do, display a very specific and measurable difference that is extremely rare in the general, unaffected population, Mosconi says. "So when you do see some subtle deviation, that's very important," he notes.
The oculomotor deficits are subtle enough to "require very sensitive lab tests" to detect them, Mosconi says. Other differences in behavior and communication that have been found in some first-degree nonafflicted relatives of people with autism are more noticeable and can sometimes be detected in casual conversation.
Family members' eye-movement capabilities were not strongly correlated with their scores on other cognitive or social-behavioral tests, a result that Mosconi calls "exciting." Although weak relationships are often a disappointment in disease research, he says, this trend was illuminating "because that tells us that we're getting at a different part of the puzzle"—to which "there are so many pieces," he notes.
Studying individuals and families who have these eye abnormalities might eventually be able to shed light on the genetics behind the affected parts of the brain, Mosconi notes. "We wanted to move even a step closer—to try to attach these broader characteristics to genes," he says. Evidence that eye-tracking trouble is prevalent in some autistic individuals and their families suggests that abnormalities in the cerebellum—which helps control motor skills, attention and language—might be to blame. And that would mean that researchers could next "look in a much more focused way [for] specific genes that might be involved in cerebellar development."
But with genetic or other profiles for autistic risk still far off, Mosconi notes that simple tests such as those for eye movements or cognitive deficits could be used in the meantime to indicate a couple's risk of having an autistic child. And he and his colleagues are looking into shoring up the specificity of odds; some of the eye-movement patterns were specific to autism whereas others had similarities to other disorders, such as schizophrenia.
Although this study was relatively small and not designed to develop theories about disorder heritability risk and eye-movement abnormalities, Mosconi notes that potentially "there would be greater risk [of having a child with autism] if both parents are showing it."
But more research needs to be done to home in on how these patterns correlate with risk. And because not all of those with autism exhibit eye-movement abnormalities, it would not be a universal test. Nevertheless, eye and other cognitive exams are highly practical. "They're quick and sensitive tests, which is exciting," Mosconi says.