Hereditary vitamin D resistant rickets (HVDRR) case series: phenotype, genotype, conventional treatment, and...

Hereditary vitamin D resistant rickets (HVDRR) is a rare autosomal recessive disorder marked by end-organ resistance of 1,25-dihydroxyvitamin D secondary to various mutations in the vitamin D receptor gene. The currently accepted treatment modality involves bypassing the affected receptors in the gut with high-dose intravenous calcium. In a few limited case reports, cinacalcet, a calcimimetic, has been used as an adjunctive therapy.

Retrospective chart reviews were conducted to collect the clinical and biochemical data of 8 patients with HVDRR from 5 Saudi families. Four patients received only high-dose calcium, while the remaining 4 received adjuvant cinacalcet. Serum chemistry and PTH levels were measured before and during cinacalcet treatment. Gene sequencing was performed to identify the disease-causing mutation.

All 8 patients exhibited alopecia and secondary hyperparathyroidism. Other clinical and biochemical features of rickets were present to varying degrees. Genetic analysis revealed 3 distinct mutations: a ligand-binding domain mutation in 3 unrelated patients, a ligand-binding domain mutation in 2 sisters, and a missense DNA-binding domain mutation in 3 brothers. While the overall response to therapy was variable, none of the 4 patients who received adjunctive cinacalcet developed hypocalcaemia, and there was some initial promise in improving serum PTH levels.

This series provides new insight into the clinical and biochemical characteristics as well as treatment responses in Saudi children with HVDRR. The findings suggest that cinacalcet is a safe and potentially valuable adjuvant in this understudied population; however, further research is required to verify these results.