Association between PNPO and schizophrenia in the Japanese population

Accumulating evidence suggests that both homocysteine metabolism and monoaminergic neurotransmitter systems are important in schizophrenia pathology. We hypothesized that the gene PNPO (pyridoxine 5′-phosphatase oxidase gene) might be a candidate for susceptibility to schizophrenia because PNPO encodes pyridoxamine 5′-phosphate oxidase (EC 1.4.3.5), a rate-limiting enzyme in pyridoxal 5′-phosphate (PLP, vitamin B6) synthesis. PLP is a metabolically-active form of vitamin B6 and thus, is required as a co-factor for enzymes involved in both homocysteine metabolism and synthesis of neurotransmitters such as catecholamine. We examined 8 single nucleotide polymorphisms (SNPs) in PNPO and its 5′-flanking regions in 359 schizophrenia patients and 582 control subjects. Four marker regions of PNPO showed significant levels of allelic associations with schizophrenia (the highest was rs2325751, P = 0.004). In addition, the haplotype case–control study revealed a significant association (permutation P < 0.00001) between PNPO and schizophrenia. These findings suggest that variations in PNPO may contribute to overall genetic risk for schizophrenia in the Japanese population.