Population studies have shown that a portion of people with autism suffer from constipation and other gastrointestinal problems. A subset of these individuals also have “leaky guts”—that is, weakened intestinal walls that allow undesirable compounds to enter the bloodstream. Seeking to understand these phenomena, Sarkis K. Mazmanian and Paul H. Patterson of Caltech and colleagues studied the intestines of mice that display autismlike behaviors such as repetitive movements, antisocial tendencies, and impaired communication. The researchers generated these mice—a common animal model for autism—by triggering a severe immune reaction in pregnant females. In addition to exhibiting autistic behaviors, the offspring born to these females had leaky guts. A few weeks after treating the newborns with a one-week course of Bacteroides fragilis, a probiotic, or beneficial gut bacterium, the team found that the mice had stronger intestinal walls, vocalized more, and repeated motions less than their nontreated counterparts (Cell 2013, DOI: 10.1016/j.cell.2013.11.024). Autism is a heterogeneous disorder that involves many genes, Mazmanian notes. But he says his team’s findings suggest that gut physiology plays a role and could lead to new treatments.