Vitamin D binding protein (DBP) levels during tuberculosis treatment are affected by DBP genotype / haplotype but not by total vitamin D levels

Abstract

Background: Vitamin D Binding Protein (DBP), also known as group specific component of serum (Gc-globulin) has been associated with susceptibility to tuberculosis. Its functions are varied including internalisation of vitamin D and conversion to macrophage activating factor (MAF). Single nucleotide polymorphisms (SNPs) at exon 11(rs7041 and rs4588) result in GC1 and GC2 variants ( GC1 subdivided into GC1S and GC1F) . Methods: In an open label observational trial, patients with mycobacterial infection were supplemented with 100,000 units of cholecalciferol every 8 weeks and baseline bloods, vitamin D, DBP levels and various SNPs in the vitamin D axis were recorded. Results: In 49 active tuberculosis patients studied, the median vitamin D level was 12.1nmol/l. Vitamin D levels and DBP levels rose significantly (p There was no significant difference in baseline DBP levels in those who were severely deficient (25(OH)D levels ≤20nmol ) and those with levels >20nmol/l. This study shows that GC haplotype significantly affects the DBP level (p=0.022). Levels of DBP are higher with GC1S carriage and lower with GC1F carriage, with GC2 carriage DBP levels lying in between. Conclusion: Vitamin D does not influence DBP levels whilst genotype and haplotype influences DBP levels during mycobacterial infection.