Despite decades of extensive research, the precise causes of autism are still a mystery.
About 1 in 36 US children have been diagnosed with autism, a complex group of developmental conditions characterized by repetitive behaviors and difficulties with social interactions. Recent studies have suggested that maternal sickness during pregnancy increases the risk of autism in the child.
But new research from NYU Langone Health found “no convincing evidence” that autism can be caused by a mother contracting an infection, suffering depression or having other health troubles while pregnant.
Instead, the researchers said autism diagnoses can often be chalked up to genetics, exposure to pollution and access to healthcare.
“We saw no association between the individual [diagnostic codes on medical records] indicating maternal infection and [a child’s] autism diagnosis,” senior study author Magdalena Janecka told The Post, “however, we cannot say conclusively that maternal infection does not cause autism.”
Inside the ‘first’ of its kind study
Janecka’s team analyzed more than 1.1 million Danish pregnancies. Denmark’s registry data is better organized and more comprehensive than the US system, said Janecka, an associate professor in the Department of Child and Adolescent Psychiatry and the Department of Population Health at NYU Grossman School of Medicine.
Researchers narrowed their focus to 236 maternal conditions reported in the health records. They were able to attribute most of the children’s autism diagnoses to factors such as the mother’s age during pregnancy — kids of older mothers are more likely to have autism — and genetics.
For example, the researchers said if a woman experiences depression during her pregnancy and her child is diagnosed with autism, it’s much more likely the pair share genes that cause both conditions instead of the depression causing autism in the developing fetus.
“Many mothers of children with autism feel guilty about it,” said Janecka, “thinking that they did something wrong during pregnancy, and it is heartbreaking.”
She told The Post that over 350 genes are associated with autism and developmental delay — and many more likely contribute.
“These 350 genes are associated with particularly high risk and often occur de novo in the child — i.e. the mutation occurs only in parents’ sperm or egg, so both parents are unaffected but the mutation is passed to the child,” Janecka explained. “If the child has one of these mutations, they are very likely to be diagnosed with autism or [developmental delay].”
Beyond the mother’s medical history
When the explanation wasn’t immediately clear, the researchers included siblings in the analysis. If a mother was diagnosed with the same condition while pregnant with her child with autism and her child without autism, that would suggest other factors were at play.
“We believe our study is the first to comprehensively examine the entire medical history of the mother and explore a wide range of possible associations, controlling for multiple concurrent conditions and confounding factors,” said lead study author Dr. Vahe Khachadourian, a research assistant professor in the Department of Child and Adolescent Psychiatry at NYU Grossman School of Medicine.
The team also analyzed fathers’ medical histories. After accounting for familial factors, the only maternal diagnosis still strongly linked to autism was pregnancy complications related to the fetus.
“Our interpretation is that these fetal diagnoses likely do not cause autism, but are instead early signs of it,” Janecka said. “The predominant hypothesis is that autism really starts prenatally. Even before a child receives a diagnosis for autism, developmental changes have been happening the entire time.”
What’s next for the research
There were limitations to the study, published Friday in the journal Nature Medicine. For instance, researchers didn’t analyze medication use during pregnancy.
Janecka told The Post the team plans to use genetic data from the children it studied to identify which maternal conditions are most indicative of elevated genetic predisposition to autism.
In the meantime, autism diagnosis rates continue to rise. Researchers have speculated that much of the surge may be due to enhanced screening practices, diagnostic criteria changes and increased awareness among parents and clinicians.
For pregnant couples worried about their child’s autism risk, Janecka recommends seeing a genetic counselor.
“It appears that autism occurs largely due to genetic factors, which are difficult to test for,” she noted. “If a couple has a history of autism among their close family members, they can speak to a genetic counselor to learn about the likelihood their child will also have the diagnosis.”
