Finally, two studies by a Japanese group have examined the association of NMDA-related genes in schizophrenia. Prior studies in Caucasians have found associations with glutathione-synthesis-related genes, but an attempt [9] to replicate this finding in the Japanese population found no significant associations with schizophrenia. In another study [10] by the same group, associations with D-amino acid-oxidase-related genes were examined in 1656 Japanese schizophrenia patients and 1842 matched controls. Again, no significant associations were seen. As prior studies in other groups were strongly positive, the authors concluded that ethnic differences might have led to the negative result.
