A rationale for treatment of hereditary vitamin D-resistant rickets with analogs of 1α,25-dihydroxyvitamin D3

Hereditary vitamin D-resistant rickets (HVDRR) is caused by heterogeneous inactivating mutations in the vitamin D receptor (VDR). Treatment of HVDRR patients with high doses of oral calcium and supraphysiologic doses of 1 alpha ,25-dihydroxyvitamin D-3 (1,25D(3)) has had limited success. In this study we explored the use of vitamin D analogs as a potential therapy for this disorder. The rationale for the use of vitamin D analogs is that they bind the VDR at different amino acid residues than 1,25D(3), and their ability to modulate VDR functions differs from that of the natural hormone. In this report, we examined the VDR from three HVDRR patients with mutations in the ligand-binding domain of the VDR (histidine 305 to glut mine, arginine 274 to leucine, and phenylalanine 251 to cysteine) for their responses to two vitamin D analogs, 20-epi-1,25D(3) and 1 beta -hydroxymethyl-3-epi-16-ene-26a,27a-bishomo-25D(3) (JK-1626-2). Our results reveal that vitamin D analogs partially or completely restore the responsiveness of the mutated VDR. Analog treatment seemed to be more successful when the mutation affects the amino acids directly involved in ligand binding rather than amino acids that contribute to a functional VDR interface with dimerization partners or coactivators of transcription.