Researchers have discovered a biomarker that can detect autism spectrum disorder (ASD) in preschool-aged children. The new study found that levels of the protein FABP4 were much lower in four- to six-year-old children with ASD than they were in other typically developing children. Experiments in mice that lacked FABP4 revealed changes in neurons that resemble those found in the postmortem brains of people with ASD.