Does leaky gut syndrome really cause autism?

No: Many kids with autism have digestive problems. There is a problem with the calcium channels at the cell level in autistic spectrum disorders in both brain cells and some of the cells in certain parts of the digestive system. But the digestive problems are just another symptom, not the cause of the disorder.

No: "Leaky gut" is a pop diagnosis with just enough possible scientific basis to make it interesting. A scientifically-sound lab test (sucrose / mannitol) is available. In Crohn's and ulcerative gut disease, the leak is obvious but there's no increase in mental illness or most of the other diseases that folks attribute to "leaky gut". I'd be caution, and report anyone making this claim.