 The purpose of this study is to assess the efficacy of oral glycine as an augmentation strategy in two psychotic patients with a triplication 4 copies of the gene glycine decarboxylase GLDC. Subjects will first undergo a double-blind placebo-controlled clinical trial in which one 6-week arm will involve glycine maximum daily dose of 0.8 gkg, administered on a TID dosing schedule and one 6-week arm will involve placebo. A 2-week period of no treatment will occur between treatment arms. A 6-week period of open-label glycine maximum daily dose of 0.8 gkg, administered on a TID dosing schedule will follow the double-blind placebo-controlled clinical trial. Prior to the double-blind placebo-controlled clinical trial and at the end of the open-label glycine trial, the following procedures will be carried out: structural MRI 3T, Proton 1H MRS 4T, fMRI 3T, steady-state visual evoked potentials, and EEG. Positive, negative, and affective symptoms and neurocognitive function as well as plasma levels of large neutral and large and small neutral and excitatory amino acids and psychotropic drug levels will be assessed periodically. In addition, 1H MRS 4T for 2 hours after a single oral dose of a glycine-containing drink will be assessed at baseline. Pharmaceutical grade glycine powder Ajinomoto or placebo will be dissolved in 20 solution and prepared by the McLean Hospital Pharmacy. 