Vitamin D binding protein gene polymorphisms and chronic obstructive pulmonary disease: a meta-analysis

Background: A number of polymorphisms in vitamin D binding protein (VDBP) (GC) gene have been implicated in risk of chronic obstructive pulmonary disease (COPD), but the results were controversial. GC1F, GC1S, and GC2 are three common variants of the VDBP gene [single nucleotide polymorphisms (SNPs): rs7041 and rs4588], which were reported to be associated with COPD. This study aimed to explore the association between VDBP gene polymorphisms and COPD. Methods: PubMed, EMBASE, Web of Science (Medline) and Chinese National Knowledge Infrastructure (CNKI) were searched for eligible case-control studies. Study quality was evaluated using the Newcastleottawa quality assessment scale (NOS). After the most appreciated genetic model was identified, a metaanalysis was performed to test the association between VDBP gene polymorphism and COPD. The pooled odds ratios (ORs) were performed respectively for the most appreciated genetic model, single allele comparison and homozygous gene model analysis. Summary receiver operating characteristic curve (SROC) analyses were applied to evaluate the diagnostic performance of polymorphism of VDBP to COPD. Results: Eight studies containing 2,216 participants were included. The analyses of the most appropriate genetic models offered significant results in recessive model of GC1F/1S group (OR = 2.18), co-dominant genetic model in GC1F/2 group (1F-1F vs. 2-2: OR = 4.87; 1F-2 vs. 2-2: OR = 1.73; 1F-1F vs. 1F-2: OR = 2.27). In single allele comparison, significant results were obtained in GC1F vs. GC1S and GC1F vs. GC2, with ORs were 1.47 and 1.77, respectively. In homozygous genes comparison, the OR was 2.51 in GC1F homozygote vs. other genotypes. Subgroup analyses offered the same significant results in Asian population, but not in Caucasian population. The SROC analyses showed the less accurate performance of polymorphism of VDBP to COPD. Conclusions: There is a close association between COPD and GC gene polymorphisms. The GC1F allele could be a risk factor, the GC1S and GC2 allele may be protective factors in Asian, but not in Caucasians.