Table 1.

Studies investigating VDR gene polymorphisms, CYP2R1 variants, and asthma susceptibility in different populations

Study	N	Polymorphisms investigated	Population	Outcome
Fang et al31	101	VDR SNPs	Chinese	No association between Fok I and Bsm I polymorphisms of VDR gene and asthma development
Li et al32	467	Eight exons of VDR and all five exons of CYP2R1	Chinese Han	Association between GC variants and asthma susceptibility
Pillai et al33	139	12 SNPs in VDR, CYP24A1, and CYP2R1	Young African Americans	Association between CYP2R1 (SNP rs10766197) homozygous minor genotype and asthma. Association between CYP24A1 (SNP rs2248137) and lower vitamin D levels
Maalmi et al30	155	VDR SNPs	Tunisian children	No association between VDR SNPs and serum 25(OH)D levels. Association between VDR gene polymorphisms and susceptibility to asthma

Abbreviations: VDR, vitamin D receptor; SNP, single-nucleotide polymorphism; 25(OH)D, serum 25-hydroxyvitamin D.