RT Journal Article SR Electronic T1 Decreased serum pyridoxal levels in schizophrenia: meta-analysis and Mendelian randomization analysis JF Journal of Psychiatry and Neuroscience JO J Psychiatry Neurosci FD Canadian Medical Association SP 194 OP 200 DO 10.1503/jpn.170053 VO 43 IS 3 A1 Yukiko Tomioka A1 Shusuke Numata A1 Makoto Kinoshita A1 Hidehiro Umehara A1 Shin-ya Watanabe A1 Masahito Nakataki A1 Yoshimi Iwayama A1 Tomoko Toyota A1 Masashi Ikeda A1 Hidenaga Yamamori A1 Shinji Shimodera A1 Atsushi Tajima A1 Ryota Hashimoto A1 Nakao Iwata A1 Takeo Yoshikawa A1 Tetsuro Ohmori YR 2018 UL http://jpn.ca/content/43/3/194.abstract AB Background: Alterations in one-carbon metabolism have been associated with schizophrenia, and vitamin B6 is one of the key components in this pathway.Methods: We first conducted a case–control study of serum pyridoxal levels and schizophrenia in a large Japanese cohort (n = 1276). Subsequently, we conducted a meta-analysis of association studies (n = 2125). Second, we investigated whether rs4654748, which was identified in a genome-wide association study as a vitamin B6-related single nucleotide polymorphism, was genetically implicated in patients with schizophrenia in the Japanese population (n = 10 689). Finally, we assessed the effect of serum pyridoxal levels on schizophrenia risk using a Mendelian randomization (MR) approach.Results: Serum pyridoxal levels were significantly lower in patients with schizophrenia than in controls, not only in our cohort, but also in the pooled data set of the meta-analysis of association studies (standardized mean difference −0.48, 95% confidence interval [CI] −0.57 to −0.39, p = 9.8 × 10−24). We failed to find a significant association between rs4654748 and schizophrenia. Furthermore, an MR analysis failed to find a causal relationship between pyridoxal levels and schizophrenia risk (odds ratio 0.99, 95% CI 0.65–1.51, p = 0.96).Limitations: Food consumption and medications may have affected serum pyridoxal levels in our cross-sectional study. Sample size, number of instrumental variables and substantial heterogeneity among patients with schizophrenia are limitations of an MR analysis.Conclusion: We found decreased serum pyridoxal levels in patients with schizophrenia in this observational study. However, we failed to obtain data supporting a causal relationship between pyridoxal levels and schizophrenia risk using the MR approach.