Decades of research show that autism has no single cause. Experts agree that it results from a complex interaction between genes and the environment, unique to each individual.
“What causes autism in one person is unlikely to be the cause in another,” says Laura Grofer Klinger, PhD, executive director of the UNC TEACCH Autism Program. “It’s a gene-environment interaction, and that’s what makes it so complicated.”
Families and individuals with autism naturally seek answers about why their brains work differently. At the same time, misinformation makes understanding the condition even harder. Evidence-based research, however, provides some insights.
Genetics and Family Links
UNC researchers, studying autism for more than 50 years, have found that autism often runs in families. About 20% of babies with an older sibling on the spectrum will develop autism, and identical twins show a particularly high concordance. Children with certain genetic disorders, such as Fragile X syndrome, also have a higher likelihood of autism.
Scientists have identified hundreds of genetic changes linked to autism, though the full picture is still unclear. “Sometimes these changes are inherited; sometimes they happen spontaneously,” says Rebecca Baum, MD, chief of UNC’s Division of Developmental Behavioral Pediatrics.
UNC studies using MRI scans revealed that brain differences appear in six-month-old infant siblings of children with autism, even before behavioral signs emerge. “Brain changes are present long before symptoms appear,” Dr. Klinger says.
Environmental Factors in the Womb
Exposure to environmental factors during pregnancy may also influence autism risk. Research points to air pollution, maternal infections or fevers, and certain pregnancy complications as potential contributors.
Some studies have examined medications, including acetaminophen (Tylenol). While a few studies suggested a possible link, larger and more reliable research has found no clear association. “Untreated fever poses a higher risk than taking Tylenol,” Dr. Klinger emphasizes.
Parental Age
Children born to older parents may have a slightly higher risk of autism. Theories include increased pregnancy complications for older mothers and higher likelihood of genetic mutations in sperm from older fathers. Overall, the risk remains low, and more research is needed.
Vaccines and Autism
Extensive research has shown that vaccines do not cause autism. Early symptoms typically appear between 15 months and three years, coinciding with routine vaccinations, which sometimes leads parents to mistakenly associate the two.
Rising Autism Rates
Autism diagnoses have risen dramatically: in 2000, about 1 in 150 children were diagnosed; today, it is 1 in 31. Experts say this is partly due to greater awareness among parents and pediatricians and changes in diagnostic criteria. Today, autism is recognized as a spectrum, including individuals without intellectual disabilities, expanding the number of people who meet the criteria.
“Many children from the 1980s would be diagnosed under today’s standards, and some are now being diagnosed as adults,” Dr. Klinger notes.
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