The results are the first to suggest a trans-generational contributor to the developmental disorder.
The study, published in the journal JAMA Psychiatry, is the first to examine the potential legacy that a mother’s experience with childhood abuse could have on the health of her own children. The findings are especially sobering given the latest statistics released from the Centers for Disease Control, which found a significantly higher rate of autism spectrum disorders (ASD) — one in 50 compared to one in 88 from a report released in 2012 — among school-aged children than previously thought.
The authors of the JAMA Psychiatry paper studied more than 50,000 women enrolled in the Nurse’s Health Study II, who were asked about any history of abuse before they were 12. The questions delved into both physical and emotional abuse, as the women evaluated whether they had been hit hard enough to leave bruises, as well as whether adults or caregivers had insulted, screamed or yelled at them. They also filled out questionnaires about whether their own children were diagnosed with autism spectrum disorders. The scientists also had access to the nurses’ health records, so they could adjust for other maternal health factors known to influence autism risk, including nine pregnancy-related conditions such as preeclampsia, gestational diabetes, alcohol consumption and smoking.
Women who reported physical, emotional, or sexual abuse when they were young were more likely to have a child with autism compared to women who were not abused. The more severely the women were abused, the higher their chances of having a child with autism; compared to women who weren’t abused, those who endured the most serious mistreatment were 60% as likely to have an autistic child.
Because it’s possible that a mother’s exposure to abuse as a child could also lead her to engage in behaviors associated with harming the fetus — such as smoking, drinking during pregnancy, using drugs, being overweight, having preterm labor or giving birth to a premature or low birth weight baby — the scientists also calculated how much these factors contributed to the risk of ASD in the next generation. To their surprise, these conditions explained only 7% of the heightened risk among the abused women. That meant that abuse was exerting more lasting effects on the women’s bodies that were translating into an increased risk of autism in their children.
How? The researchers believe that some of the lifestyle circumstances associated with abuse, such as poor nutrition, could be responsible for some of the association. It’s also possible that abuse causes biological changes in a woman’s immune system, including disruption of the stress response, that could lead to harmful effects on a developing fetus. Studies have shown that autistic children showed abnormal stress responses, and it’s possible that a mother’s altered stress reaction could be passed on to her child. “Maternal inflammation affects the developing brain, and maternal inflammation and immune function have been hypothesized to be causes of autism,” the researchers write.
The researchers also speculate that childhood abuse can leave women in a state of chronic stress; the constant release of stress-related hormones could also increase a developing child’s chances of developing autism, since such androgens have been associated with autistic symptoms. Finally, a mother’s childhood abuse could be an indicator of a genetic risk for mental illness, which is often associated with abuse of youngsters. Studies showed that mental illness and autism may share genetic risk factors, “therefore, the perpetration of child abuse by grandparents and experience of abuse in childhood by the mother may be indicators of genetic risk for autism in the child,” the study authors write.
“Childhood abuse is associated with a wide array of health problems in the person who experiences it, including both mental health outcomes like depression and anxiety, and physical health outcomes like depression and anxiety, and physical health outcomes like obesity and lung disease,” said senior study author Marc Weisskopf, an associate professor of environmental and occupational epidemiology at Harvard School of Public Health, in a statement. “Our research suggests that the effects of childhood abuse may also reach across generations.”
Is that legacy enough to explain the apparent rise in ASD documented in the most recent government data? The CDC data was based on parental reports of autism; a representative sample of parents were asked whether a doctor had diagnosed their child with autism, and some experts caution that such reports are not as reliable as health records documenting the disorder. Still, the latest statistics suggest that at least awareness of ASDs is increasing, and with it, potential explanations for what might be contributing to the disorder.
If childhood abuse turns out to be one of these reasons for the rise in autism cases, then efforts to prevent it take on new urgency, since such interventions can benefit more than just one victim.