GAD1 and autism: In the last decade, biochemical studies have revealed that there are highly significantly decreased levels of key synthesizing enzymes for GABA, glutamic acid decarboxylase type 65 and 67 (GAD65 and GAD67 isoforms) in the cerebellum and parietal cortex in autism (Fatemi et al., 2014) further suggesting that there are effects on the GABA system in the autistic brain.