Google "MTHFR" and "autism" and other terms related to autism.

MTHFR stands for "methylene tetrahydrofolate reductase".   It's a key enzyme involved in metabolic pathways involved with folate and vitamin B12 (the methyl form).    A lack of it means that, among other things, toxic substances build up and impair biological processes in the body.   This is an area of medicine that has emerged in the last decade or so. 

There is genetic testing that corresponds to this enzyme's function being impaired.   There are other, similar, tests as well for markers like one called CBS and both forms of cobalamin (methyl and adenosyl) that could also be involved -- don't overlook this.   Do the genetic tests and find a good and experienced functional medicine expert.   You may need to look to the US for the functional medicine.   The testing can be done in Canada through Lifelabs Genetics.

With patience and applied functional medicine, autism can definitely be managed and even reversed.