75% of ASD patients test positive for folate receptor alpha antibodies (FRAA). FRAA block folate uptake in the brain and cause ASD. These antibodies bind with higher affinity to bovine folate receptors. This points to bovine folate receptor protein being the antigen that resulted in the synthesis of FRAA. Bovine folate receptor proteins are present in cow's milk. Cow's milk proteins contaminate numerous vaccines. Casein and casamino acids used as growth media for vaccine antigens are cow's milk derived. Women vaccinated with cow's milk contaminated proteins can synthesize FRAA. These FRAA can block folate uptake in the fetal brain. Detailed mechanism of disease causation and its similarity to the food allergy development process, are described.