Background: We report a novel mutation in a case of hereditary vitamin D resistant rickets (HVDRR) without alopecia and successful management of this condition with the intravenous formulation of calcium chloride delivered via gastric tube.
Clinical case: A 22 month old male (length -3.4 SDS; weight -2.1 SDS) presented with failure to thrive, short stature, severe hypocalcemia and gross motor delay. He did not have alopecia. Initial blood tests and history were thought possibly to suggest vitamin D deficiency rickets: calcium 5.1mg/dL, (8.8-10.8); phosphorus 4.1mg/dL, (4.5-5.5); alkaline phosphatase 1481 U/L (80-220); intact PTH 537.1 pg/mL (10-71). Subsequently, vitamin D studies returned that were consistent with HVDRR: 25-hydroxyvitamin D 34 ng/mL (20-100); 1,25-dihydroxyvitamin D 507 pg/mL. This diagnosis was confirmed by DNA sequencing. His subsequent clinical course was complicated by the fact that IV calcium was not a viable option for this patient, and his calcium levels could not be well controlled on oral calcium citrate or calcium glubionate therapy. Eventually, we were able to maintain calcium levels above 8 mg/dL using the intravenous preparation of calcium chloride administered via gastric tube.
Genetic studies: A unique homozygous T to C base substitution was found in exon 6 in the vitamin D receptor (VDR) gene. This mutation causes leucine to be converted to proline at position 227 in helix 3 in the VDR ligand binding domain (LBD). The mutation rendered the VDR non-functional, leading to HVDRR, with absence of alopecia.
Conclusion: HVDRR should be considered in a patient with profound hypocalcemia which is refractory to conventional therapy of vitamin D deficiency rickets even without evidence of alopecia. We report the first case of HVDRR with a novel mutation in the LBD that was successfully treated with enteral treatment using a calcium chloride infusion.
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