The association between vitamin D receptor gene polymorphisms and asthma: a systematic review and meta-analysis

Numerous studies have reported on the genetic factors related to asthma. In recent years, the vitamin D receptor (VDR) has been identified as one of the asthma susceptibility genes that is closely associated with the pathogenesis of asthma. Randomized controlled trials (RCTs) related to asthma and the VDR were identified from the Chinese and English databases. The following keywords were used as search terms: "asthma", "vitamin D receptor", "VDR", "polymorphism", and "mutation". Meta-analysis was performed using RevMan 5.3 and Stata 13 software provided by the Cochrane system. A total of 7 RCTs were included in this meta-analysis, 6 of which described the correct random allocation methods, 6 described the allocation plan in detail, and 4 used the blinding method. The frequency of the CC + CA dominant genotype at the Apa I locus and the GG + GA genotype frequency at the Bsm I locus of the VDR gene were significantly higher in asthmatic patients compared to control healthy patients [odds ratio (OR) =0.81, 95% confidence interval (CI): 0.68 to 0.98, P=0.03