What is receptor defect rickets (type II vitamin D–dependent rickets)?

Updated: Jun 19, 2020
  • Author: Horacio B Plotkin, MD, FAAP; Chief Editor: Jatinder Bhatia, MBBS, FAAP  more...
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Receptor defect rickets (type II vitamin D–dependent rickets)

Receptor defect rickets (hereditary 1,25-dihydroxyvitamin D–resistant rickets [HVDRR]) results from a recessively inherited abnormality in the calcitriol receptor, causing an end-organ resistance to the vitamin.

The clinical picture, which is evident early in life, consists of rickets with very severe hypocalcemia and alopecia, although a variant without alopecia has been reported. Patients without alopecia appear to respond better to treatment with vitamin D metabolites. Serum levels of 1,25(OH)2 vitamin D3 are typically elevated. HVDRR can be lethal in the perinatal period. Because calciferol receptors are in many tissues, other, more subtle dysfunctions may occur. Patients are hypocalcemic and usually normophosphatemic.

Several mutant forms of receptor defect rickets are recognized, with a wide range of severity and response to calcitriol therapy. Some patients are totally resistant to therapy. Some others have benefited from intravenous calcium (400-1400mg/m2/day) followed by oral therapy with high doses of calcium (with secondary risk of nephrocalcinosis, hypercalciuria, nephrolithiasis, and cardiac arrhythmias). Patients with mutations in the ligand-binding domain (LBD) region of the receptor are more likely to respond to high-dose vitamin D treatment than are patients with mutations in the deoxyribonucleic acid (DNA)–binding domain (DBD) region of the receptor.

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