In recent years, science has made it increasingly clear that our gut microbiome—the trillions of bacteria and microorganisms living in our digestive tract—plays a far more significant role in our overall health than we once believed. From influencing our emotions and behavior to shaping our immune responses and determining our likelihood of developing chronic illnesses, the microbiome touches almost every aspect of human health.

Now, researchers have uncovered a surprising new connection: a potential link between a mother’s gut bacteria and the risk of her child developing autism. According to a groundbreaking study published in The Journal of Immunology, scientists from the University of Virginia School of Medicine have discovered that the gut microbiome of a pregnant mother—not the child’s own microbiome—may impact the development of autism spectrum disorder (ASD) in her offspring.

The study, led by Ph.D. candidate John Lukens, sheds light on a new biological pathway that may influence neurodevelopmental conditions. “The microbiome can shape the developing brain in multiple ways,” Lukens explained in a press release. “It’s really important for calibrating how the offspring’s immune system will respond to infection, injury, or stress later in life.”

Central to the study is a molecule called interleukin-17a (IL-17a), which is produced by the immune system and is known for its role in inflammatory responses. IL-17a has already been linked to conditions such as rheumatoid arthritis, multiple sclerosis, and psoriasis. It also helps protect the body from certain infections, especially fungal ones. However, IL-17a appears to have another powerful effect: it can influence the development of the fetal brain.

To explore this connection, the researchers conducted experiments using lab mice. Female mice from two different labs were used in the study. The first group had gut bacteria that made them more likely to produce IL-17a in response to immune stimulation, while the second group served as a control, with gut bacteria that didn’t trigger this same response.

In one part of the experiment, scientists blocked IL-17a in both groups of mice. The result? The offspring of both groups displayed typical behavior patterns after birth—essentially, no signs of autism-like symptoms. However, when the IL-17a molecule was not blocked and the pregnancy was allowed to progress normally, offspring from the first group of mice—those with gut bacteria primed for a strong IL-17a response—developed behaviors resembling those seen in autism, including impaired social interactions and repetitive actions.

To confirm that the gut bacteria were the root of this effect, researchers went a step further. They performed fecal transplants, introducing the gut bacteria from the first group of mice into those from the second group. The idea was to replicate the microbiome environment from the autism-prone mice in the control mice. As expected, once the second group adopted the new microbiota, their offspring began showing the same autism-like traits.

This research provides compelling evidence that the gut microbiome of a pregnant mother can influence the neurological development of her child, at least in animal models. Though these findings cannot yet be directly applied to humans, they offer an exciting and potentially groundbreaking direction for autism research.

“This is only the beginning,” said Lukens. “Our next step is to investigate whether similar microbiome-related patterns can be observed in human pregnancies. We also want to better understand what specific components or bacteria in the mother’s gut are contributing to this effect.”

Lukens emphasized that IL-17a may only be one part of a much larger and more complex picture. There are likely many other molecules and immune pathways involved in neurodevelopment, and it’s too early to say that this is the definitive cause of autism. Still, the findings highlight a previously underappreciated factor that may contribute to the condition.

Autism spectrum disorder is a complex and multifaceted condition with many potential contributing factors, including genetics, environmental exposures, and now—possibly—gut health. If further research confirms a similar relationship in humans, it could open the door to new preventative strategies. For example, improving maternal gut health through diet, probiotics, or other interventions could one day reduce the risk of autism in future generations.

At the very least, this study underscores how interconnected the body’s systems truly are. A mother’s gut bacteria, which we typically associate with digestion, could be influencing something as complex as her child’s brain development. It’s a humbling reminder of how much we still have to learn—and how seemingly unrelated parts of the body can play surprising roles in health and disease.