In The Politics of Autism, I discuss various ideas about what causes the condition. Here is just a partial list of correlates, risk factors, and possible causes that have been the subject of serious studies:
- Air pollution and proximity to freeways;
- Maternal thyroid issues;
- Autoimmune disorders;
- Induced labor;
- Preterm birth;
- Birth by cesarean section;
- Anesthesia during cesarean sections;
- Maternal and paternal obesity;
- Maternal diabetes;
- Maternal and paternal age;
- Grandparental age;
- Maternal post-traumatic stress disorder;
- Smoking during pregnancy;
- Cannibis use during pregnancy;
- Antidepressant use during pregnancy;
- Polycystic ovary syndrome;
- Infant opioid withdrawal;
- Zinc deficiency;
- Sulfate deficiency;
- Processed foods;
- Maternal occupational exposure to solvents;
- Estrogen in the womb;
- Morning sickness;
- Paternal family history.
In a study of medical registry records of nearly 400,000 parent-child pairs from Denmark, a Yale School of Public Health study found that parents who were themselves born very prematurely were nearly twice as likely to have children with autism spectrum disorder.
The study, recently published in the International Journal of Epidemiology, provides solid evidence that autism spectrum disorder risk factors can span multiple generations — a new hypothesis that previously lacked much empirical evidence in humans. According to senior author Zeyan Liew, assistant professor in the Department of Environmental Health Sciences, these findings can help spark further research into the underlying mechanisms of autism risk transmission in families.
“It’s already well established that preterm birth and low birth weight of the child are risk factors for autism,” he said. “But this is the first study to show that parental preterm birth and low birth weight might carry some risk for their future offspring as well.”
For their research, Liew and his team evaluated data collected from families across Denmark from 1978 to 2017 as part of its central medical records database. Researchers linked birth records of the parents to the medical records in their offspring to investigate whether there is a link between neonatal characteristics of the parents and autism spectrum disorder risk in their children. Their results suggest that women and men who were born at less than 37 weeks or low birth weight were more likely to have children diagnosed with autism spectrum disorder than those without adverse birth characteristics. The study authors reported that some other possible multigenerational risk factors they analyzed, such as grandparents’ education, place of residence, and their age at the time of pregnancy, only contributed minimally to the observed associations.
It remains unclear how exactly autism spectrum disorder risks travel across generations, but Liew said he has some hypotheses. For one, there has been growing evidence showing that changes in gene activity in response to environmental stimuli could be inherited across generations without changing the underlying DNA sequences — a phenomenon known as epigenetic inheritance. “These adverse characteristics at birth may act as a proxy measure of possible heritable epigenetic modifications as a result of harmful prenatal exposures affecting early life growth, which could help explain the multigenerational transmission of disease risk we observed,” Liew said.
This is the first study to show that parental preterm and low birth weight might carry some risk for their future offspring as well.Zeyan Liew