Recent studies show that our gut microbiome deeply affects health — influencing “our response to fear and negative stimuli,” weight, mental health, and even autoimmune diseases. A new study in The Journal of Immunology adds autism to that list, linking the condition not to a child’s microbiome, but to the mother’s.

“The microbiome can shape the developing brain in multiple ways,” said lead researcher John Lukens from the University of Virginia. It helps “calibrate how the offspring’s immune system is going to respond to an infection or injury or stress.”

The key may be a molecule called interleukin-17a (IL-17a), known for fighting infections but also affecting brain development in the womb. Researchers tested mice with different gut microflora — one group prone to IL-17a inflammation and another not. When IL-17a was blocked, both groups gave birth to neurotypical pups. Without intervention, pups from the first group developed autism-like behaviors.

A fecal transplant confirmed the connection: transferring gut bacteria from the first group to the second caused their offspring to show the same autism-like traits.

While early and based on animal studies, the findings suggest that “the health of the mother’s gut plays at least some role” in autism development. Future research will explore whether similar patterns occur in humans.