Vitamin D Receptor Polymorphisms in Hypocalcemic Vitamin D-Resistant Rickets Carriers

Polymorphisms in vitamin D receptor genes and its relation with susceptibility to brucellosis: a case-control study

OBJECTIVE

One of the systemic infections is Brucellosis which is caused by facultative intracellular bacteria of the genus Brucella. Vitamin D is a fat-soluble prohormone, that metabolizes enzymes and its intracellular receptor creates the active hormone and also mediate in responses of immune system.

METHODS

Current research consists of 102 patients with brucellosis who were selected based on culture, PCR results serology, and clinical symptoms. The control group composed of 102 healthy people. The polymorphism of genes (Bsm I, Fok I, Taq I, Apa I) encoding Vitamin D receptor (VDR) were assessed by the PCR-RFLP method.

RESULTS

The results showed that ff, tt, aa, and bb genotypes in Fok I, ApaI, TaqI, and BsmI were significant in case/control groups (P-value ≤ 0.0001). The genotype frequency AA in the control group is higher than that of the study group, while genotype frequency aa in the study group is more than the control. The odds ratio for brucellosis in individuals with ff genotype is 37 times higher than that of Ff genotype. Also, the odds ratio of brucellosis in individuals with genotype tt, aa, and bb was 12, 53, and 6 times higher than those of the Aa, Bb, and Tt genotypes.

CONCLUSION

The genotypes aa and ff in the positions of the ApaI and FokI are of higher importance. The brucellosis risk in individuals accompanied aa genotype at Apa I is 53 times higher than that of the genotype AA, in other words, AA and BB, TT and FF genotypes are protective against the disease.

Impaired vitamin D sensitivity

Resistance to vitamin D has been known for decades as vitamin D resistant rickets, caused by mutations of the gene encoding for vitamin D receptor (VDR). Findings of extra-skeletal effects of vitamin D and learning of the molecular mechanisms used by its biologically active metabolite calcitriol revealed other ways leading to its impaired sensitivity. Calcitriol takes advantage of both genomic and non-genomic mechanisms through its binding to vitamin D receptor, located not only in the cell nuclei but also in a perinuclear space. On the genomic level the complex of calcitriol bound to VDR binds to the DNA responsive elements of the controlled gene in concert with another nuclear receptor, retinoid X receptor, and expression of the VDR itself is controlled by its own ligand. These elements were found not only in the promotor region, but are scattered over the gene DNA. The gene expression includes a number of nuclear transcription factors which interact with the responsive elements and with each other and learning how they operate would further contribute to revealing causes of the impaired vitamin D sensitivity. Finally, the examples of major disorders are provided, associated with impairment of the vitamin D function and its receptor.

Identification of a novel nonsense mutation in the ligand-binding domain of the vitamin d receptor gene and clinical description of two greek patients with hereditary vitamin d-resistant rickets and alopecia

BACKGROUND/AIMS

We analyzed the vitamin D receptor (VDR) gene in 2 Greek patients who exhibited the classical features of hereditary vitamin D-resistant rickets (HVDRR) type II, including severe bone deformities and alopecia. We also describe the clinical phenotypes and the response to treatment of our patients.

METHODS

Genomic DNA was extracted from peripheral blood samples of both patients. Coding region and flanking introns of VDR gDNA was amplified and direct sequenced.

RESULTS

A unique cytosine to thymine (C>T) transition was identified at nucleotide position 1066 (c.1066C>T) in the ligand-binding domain of the VDR gene of both patients, predicting the substitution of a glutamine to a terminal codon at position 356 (Gln356stop).

CONCLUSIONS

The novel nonsense mutation c.1066C>T (Gln356stop) is expected to result in a VDR protein 71 amino acids shorter and thus to affect the normal VDR function. In particular, the missing protein part alters the VDR heterodimerization with the retinoid X receptor which has been correlated with the presence of alopecia. Both patients were introduced to treatment with supraphysiological doses of 1α-calcidiol which improved their clinical phenotypes except for alopecia.