A new study suggests there is no evidence that the MMR jab damages the intestine and in turn causes autism. The "leaky gut" theory goes that vaccines can damage the intestine wall which, in turn, causes digestive problems. These digestive problems are believed by some to lead to the production of peptides which can damage the brain. With a study group of over two-hundred boys, the researchers found no differences in the peptide levels between the autistic and control groups.