title: Association of vitamin D receptor gene polymorphisms with asthma risk: systematic review and updated meta-analysis of case-control studies.
abstract: BACKGROUND
  The association between vitamin D receptor (VDR) polymorphisms and asthma risk has been inconsistently investigated, but published studies demonstrated conflicting results. The aim of the current study was to investigate the impact of TaqI, BsmI, ApaI, and FokI VDR polymorphisms on asthma disease by using a meta-analysis approach.
  
  
  METHODS
  Following the preferred reporting items for systematic reviews and meta-analyses guidelines, a systematic search and meta-analysis of the literature were conducted. Subgroup analyses were performed to detect potential sources of heterogeneity from selected study characteristics.
  
  
  RESULTS
  A total of 2,097 cases and 1,968 controls in eight case-control studies were included in meta-analyses. A significant association was found between TaqI polymorphisms and asthma risk [OR 1.488 (95 % CI 1.019-2.174); P = 0.040] in a codominant model. In the same way, BsmI was significantly associated with asthma risk [OR 2.017 (95 % CI 1.236-3.851); P = 0.017] in the codominant model. The homozygote BB BsmI genotype was found to confer significant asthma risk. FokI polymorphism was marginally associated with asthma risk [OR 1.187 (95 % CI 0.975-1.446); P = 0.088] in the codominant model. In contrast, no significant association was found between ApaI polymorphism and asthma risk. Subgroup analyses revealed that gender and age modified significantly the association between FokI polymorphisms and asthma risk (P = 0.035 and 0.013, respectively). Publication year and serum 25(OH) D level tended, marginally, to moderate the association between FokI polymorphism and asthma risk.
  
  
  CONCLUSIONS
  TaqI, BsmI, and FokI VDR polymorphisms contribute to asthma susceptibility. The association between FokI polymorphism and asthma risk is influenced by study characteristics.
authors.affiliation: Department of Basic Sciences, Medicine Faculty of Tunis, Tunis El Manar University, 15 Rue Djebel Lakdar, 1007, Tunis, Tunisia, kalttizaoui@gmail.com.
authors.forename: Kalthoum
authors.initials: K
authors.lastname: Tizaoui
authors.forename: Anissa
authors.initials: A
authors.lastname: Berraies
authors.forename: Besma
authors.initials: B
authors.lastname: Hamdi
authors.forename: Wajih
authors.initials: W
authors.lastname: Kaabachi
authors.forename: Kamel
authors.initials: K
authors.lastname: Hamzaoui
authors.forename: Agnès
authors.initials: A
authors.lastname: Hamzaoui
mesh_terms: D001249:Asthma / Q000453:epidemiology* / Q000235:genetics* / Q000503:physiopathology; D016022:Case-Control Studies; D005260:Female; D056726:Genetic Association Studies; D020022:Genetic Predisposition to Disease / Q000453:epidemiology*; D006801:Humans; D008297:Male; D011110:Polymorphism, Genetic; D015995:Prevalence; D018167:Receptors, Calcitriol / Q000235:genetics*; D012016:Reference Values; D018570:Risk Assessment; D012720:Severity of Illness Index
chemical_list: D018167:Receptors, Calcitriol