There are some studies that suggest a link between diet, autism spectrum disorder and gut epithelial changes. However, there is no conclusive evidence on whether gluten and/or casein have a role in influencing the behaviour, cognitive and social functioning of individuals with autism but gluten free exclusion diets may be used within complementary and alternative therapies. Currently there is not enough evidence to support the use of gluten free exclusion diets for the treatment of autistic spectrum disorders.
Further information can be found from the updated Cochrane Review: Milward C. et al. (2009) Gluten and casein-free diets for autism spectrum disorder. Cochrane Database of Systematic Reviews, Issue 2. Art. No.: CD003498.