In recent years, scientists have uncovered just how vital our gut microbiome is to our overall health. It influences everything from how we react to fear and stress, to our weight, mental well-being, and even our likelihood of developing autoimmune conditions like lupus and type 1 diabetes.

Now, new research published in The Journal of Immunology adds to this growing body of knowledge. The study, conducted using animal models, points to a link between the gut microbiome and autism—but surprisingly, it’s not the child’s microbiome that matters most. According to the researchers, it’s the mother’s microbiome that could play a key role.

“The microbiome can shape the developing brain in multiple ways,” said lead researcher John Lukens, a PhD student at the University of Virginia School of Medicine.

“The microbiome is really important to the calibration of how the offspring’s immune system is going to respond to an infection or injury or stress.”

The study focuses on a molecule called interleukin-17a (IL-17a), produced by the immune system. IL-17a has already been linked to autoimmune disorders like rheumatoid arthritis and multiple sclerosis. It’s known to help fight fungal infections, but it also appears to influence how the brain develops in the womb.