The mouse study even offers a possible explanation as to why: Childhood infections may cause the body to over-express genes that code for microglia, the central nervous system’s primary immune cells. That, in turn, can affect brain development, which could be at play in some traits commonly associated with autism, such as difficulty communicating verbally or recognizing familiar faces.

So the researchers experimented with drugs that target microglia, and found that they not only prevented those social issues in adult mice — they might have reversed them.

Among boys genetically predisposed to autism, a severe childhood infection could make that diagnosis more likely.