An Unusual Form of Vitamin D-Dependent Rickets in a Child: Alopecia and Marked End-Organ Hyposensitivity to Biologically Active Vitamin D

Abstract

A 12-yr-old female patient with an unusual form of vitamin D dependency and alopecia is described. She was a product of consanguineous mating and developed signs and symptoms suggesting vitamin D dependency early in life. Neither 150 μg/day (6 μg/kg·day) 1α-hydroxyvitamin D₃) nor 5 μg/day (0.2 μg/kg·day) 1,25-dihydroxyvitamin D₃ proved to have an effect on her abnormal serum chemistry. Seven million international units per day (about 2 × 10⁵ IU/kg·day) of native vitamin D restored her serum chemistry to normal and brought about marked improvement on skeletal radiographs, when her serum 25-hydroxyvitamin D, 1,25-dihydroxyvitamin D, and 24,25-di-hydroxyvitamin D were 4250, 4.8, and 35 ng/ml, respectively. Even with the high serum levels of vitamin D metabolites, her intestinal ⁴⁷Ca absorption rate remained in the lower normal range and urinary calcium excretion was decidedly low. Association of hypoparathyroidism was ruled out. These results suggest that this patient has extreme end-organ (intestine) hyposensitivity, probably of congenital origin, to the biologically active metabolites of vitamin D.