title: Is MTHFD1 polymorphism rs 2236225 (c.1958G>A) associated with the susceptibility of NSCL/P? A systematic review and meta-analysis.
abstract: OBJECTIVE
  To investigate the association between the methylenetetrahydrofolate dehydrogenase 1 (MTHFD1) polymorphism rs 2236225 (c.1958G>A) and susceptibility to non-syndromic cleft of the lip and/or palate (NSCL/P).
  
  
  METHODS
  An extensive literature review has been conducted using PubMed, Web of Science, Cochrane Library, Google Scholar, the China National Knowledge Infrastructure (CNKI), and Wanfang Database for eligible researches. The terms for searching were "cleft lip OR cleft palate OR CLP OR CL/P OR oral facial cleft OR OFC" AND "methylenetetrahydrofolate dehydrogenase (NADP+ dependent) 1 OR methenyltetrahydrofolate cyclohydrolase formyltetrahydrofolate synthetase OR MTHFD1 OR MTHFD". Two independent researchers screened, evaluated and extracted the data of included studies. The pooled odds ratios (OR) with 95% confidence intervals (95% CI) were calculated by random effects model under five gene models. Subgroup, sensitivity analysis and publication bias were also assessed.
  
  
  RESULTS
  Ten case-control studies have been included in the systematic review and eight studies have been considered for the meta-analysis. Overall, the MTHFD1 polymorphism rs2236225 and the risk of NSCL/P showed pooled OR (95% CI) of 1.02 (0.86-1.21) under allelic model. A higher degree of heterogeneity was observed in Asian countries (I (2) = 75.6%) compared to non-Asian countries (I (2) = 48.9%). Similar consequence appeared in the subgroup of children (I (2) = 78.6%) compared with that of mothers (I (2) = 0.0%). There was no significant difference in the publication bias by the Begg's funnel plot (P = 0.711) and Egger's regression test (P = 0.746).
  
  
  CONCLUSIONS
  Our assessment suggested there was no significant association between the MTHFD1 polymorphism rs 2236225 (c.1958G>A) and the susceptibility to NSCL/P. Further investigations using a large sample size and a more advanced technique should be adopted to reach a more precise conclusion in the future.
authors: Department of Orthodontics, Peking University School and Hospital of Stomatology, Peking, 100081, China.
authors: Huaxiang
authors: H
authors: Zhao
authors: Department of Orthodontics, Peking University School and Hospital of Stomatology, Peking, 100081, China.
authors: Jieni
authors: J
authors: Zhang
authors: Department of Orthodontics, Peking University School and Hospital of Stomatology, Peking, 100081, China.
authors: Mengqi
authors: M
authors: Zhang
authors: Bybo Dental Group, Beijing, 100062, China.
authors: Feng
authors: F
authors: Deng
authors: Department of Orthodontics, Affiliated Hospital of Stomatology, Chongqing Medical University, Chongqing, 401147, China.
authors: Leilei
authors: L
authors: Zheng
authors: Department of Orthodontics, Peking University School and Hospital of Stomatology, Peking, 100081, China.
authors: Hui
authors: H
authors: Zheng
authors: Laboratory Center, Peking University School and Hospital of Stomatology, Peking, 100081, China.
authors: Feng
authors: F
authors: Chen
authors: Department of Orthodontics, Peking University School and Hospital of Stomatology, Peking, 100081, China.
authors: Jiuxiang
authors: J
authors: Lin
keywords: MTHFD1; Meta-analysis; NSCL/P susceptibility; Polymorphisms