disorder may contribute to increased oxidation of GSH [ 47 ]. Glutathione synthesis also requires dietary glutamate and glycine. No difference in serum levels of glutamate has been reported between children with autistic disorder and controls [ 69 , 70 ], however, it was significantly higher in adults with autistic disorder [ 75 ], the level being positively correlated with social functioning as measured by the autism diagnostic interview (ADI-R) [ 103 ] which is commonly used to evaluate the core symptoms of autism which may shed light on the significantly higher level detected in mixed samples of children with autism spectrum disorders [ 86 , 87 ]. In contrast, platelet glutamic acid was significantly lower in children with autistic disorder [ 68 ]. Platelet glutamate receptors have been shown to have heightened sensitivity in major depression, schizophrenia and other psychoses [ 104 - 106 ]. This relationship has not, however, been examined in autism spectrum disorders to date. Serum and plasma glycine does not differ between children [ 60 , 69 , 70 , 86 , 87 ] or adults [ 107 ] with and without autism spectrum disorders. As glycine acts as a powerful inhibitory neurotransmitter in the brain and spinal chord [ 108 ] and glycine transporters are differentially expressed throughout the CNS [ 109 ], it may be relevant for future studies of children with autism spectrum disorders to examine whether there are abnormalities in expression of glycine transporters in the CNS or in glycine transport