BsmI, ApaI and TaqI Polymorphisms in the Vitamin D Receptor Gene (VDR) and Association with Lumbar Spine Pathologies: An Italian Case-Control Study

Abstract

Three adjacent single nucleotide polymorphisms of the vitamin D receptor gene (VDR) BsmI (rs1544410), ApaI (rs7975232), and TaqI (rs731236) are commonly studied in several pathologies. We aimed to evaluate the distribution of VDR BsmI, ApaI, and TaqI allele, genotype, and haplotype frequencies in an Italian cohort of 266 patients with lumbar spine disorders assessed by Magnetic Resonance Imaging and 252 asymptomatic controls. The exposure to putative risk factors was evaluated by a questionnaire. Polymorphisms were detected by PCR-RFLP and TaqMan® SNP Genotyping Assay. The results were statistically adjusted for the identified conventional risk factors. The three SNPs were in linkage disequilibrium. For all cases BbAaTT was a 3-fold risk factor OR = 3.38), whereas bbAATT (OR = 0.22), and bbaaTT (OR = 0.47) genotypes were found to be protective. Specifically, for patients affected by disc herniation only (n = 88) and all lumbar pathologies excluding stenosis and/or spondylolistesis (n = 215) B allele, Bb, Aa, and BbAaTT genotypes were risky, whereas b allele, bb, aa, and bbaaTT genotypes were protective. In patients affected by osteochondrosis with or without disc hernation (n = 50), T allele, Aa, and bbAaTT genotypes were risky, whereas t allele, AA, tt genotypes were protective. In patients affected by stenosis and/or spondylolistesis (n = 51) no significant associations were found. This is the first study showing an association of the three genetic VDR variants BsmI, ApaI, and TaqI and lumbar spine pathologies. Our study contributes to delineate genetic risk factors for specific subgroups of patients with lumbar spine pathologies highlighting the importance of haplotype analysis, and of detailed clinical evaluation of the patients for identification of genetic biomarkers.

Fig 1

Structure of the genomic region of the VDR and location of BsmI, ApaI and TaqI (*in the coding sequence, exon 9) SNPs located near the 3’ terminus of the gene (a). Representative gels for the determination of BsmI (b), ApaI (c) and TaqI (d) genotypes in three patients are showed. In the first lane there is a molecular weight DNA ladder (M) for size estimation of the DNA fragments. The letter “A” indicates the PCR amplicons which are of 825 bp for BsmI and 740 bp for ApaI and TaqI. After digestion of the PCR product with BsmI restriction enzyme an undigested 825 bp fragment (homozygous genotype BB), partially digested 825, 650 and 175 bp fragments (heterozygous genotype Bb), or totally digested 650 and 175 bp fragments (homozygous genotype bb) are present (b). After digestion of the PCR product with ApaI restriction enzyme an undigested 740 bp fragment (homozygous genotype AA), partially digested 740, 530 and 210 bp fragments (heterozygous genotype Aa), or totally digested 530 and 210 bp fragments (homozygous genotype aa) are present (c). After digestion of the PCR product with TaqI restriction enzyme, digested 495 and 245 bp fragments (homozygous genotype TT), partially digested 495, 290, 245 and 205 bp fragments (heterozygous genotype Tt), or totally digested 290, 245 and 205 bp fragments (homozygous genotype tt) are present (d). All the images of the original gels from which we cropped the representative images showed in Fig 1 are available as S1–S6 Figs.

Fig 2. LD plots (r²) are shown for all subjects (a), controls (b) and cases (c).