of gene combinations and the results they produce , says epidemiologist Elise Robinson of the Harvard T . H . Chan School of Public Health and an associate member of the Broad Institute . People who have both autism and intellectual disability , for example , tend to have more big-effect gene mutations than people with autism alone .
Facial communication Looking for these contributing gene variants isn ’ t simply an exercise in scientific curiosity or in finding potential targets for drug treatments . Because most of these genes direct how human brains develop and nerve cells communicate , learning about how they lead to autism can also reveal a lot about how everyone ’ s brain works .
For example , a key autism trait is atypical social behaviors , such as , sometimes , not focusing on “ social ” facial features like the eyes . Although the tendency to look into another person ’ s eyes seems like something we might learn simply from being around other people , autism research has revealed that genes underlie the instinct .
In a
2017 study , the authors first showed that identical twins are similar in how they look at a video with social content , such as faces . When viewing the same video , the identical twin pairs shifted their eyes with the same timing and focused on the same things far more than did two non-identical siblings or unrelated children . The fact that almost all twin pairs shared this tendency suggests solid genetic underpinnings for the behavior .
Having established a strong genetic contribution to this trait , the investigators , from Emory University and the Marcus Autism Center in Georgia and Washington University in St . Louis , then showed that the tendency to look at the eye and mouth areas of a human face is decreased in autistic children . They concluded that while not all of the inclination to look at certain parts of a face is genetic , much of it is .
Twin studies like this are powerful tools for evaluating how much genes dictate a feature , and such investigations reveal that the genetic contribution to autism is substantial . Autism also tends to cluster in non-twin family members : One in five infants
who has an older sibling with autism also develops it .
Genetic determinants Overall , genetics accounts for about 70 to 80 percent of factors contributing to autism , says neurologist Daniel Geschwind , director of UCLA ’ s autism research and treatment center . By comparison , a condition like depression has an underlying genetic contribution of about 50 percent , he says . Alessandro Gozzi , neuroscientist and group leader at the Istituto Italiano di Tecnologia , weights the power of genes even more , placing the shared diagnosis rate between twins as high as 95 percent , depending on how strict the diagnostic boundaries are . But regardless of the precise value , he says that the “ wide consensus ” among autism researchers is that genetics is a powerful determinant of autism .
Going the next step — finding the specific genes involved — is a monumental task . It ’ s also one that yields dividends for understanding brain function more broadly .
The candidate gene variants are today very numerous , but a few stand out for their potential to exert a large effect . Chaste cites
fragile X syndrome and
Rett syndrome as examples — both are genetic conditions ( termed syndromes because they are defined by a cluster of traits ) that are tied to variants of a single gene or chromosome
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