Vitamin D‐dependent rickets type I and type II

Abstract Two distinct hereditary defects, vitamin D‐dependent rickets type I (VDDR I) and type II (VDDR II), have been recognized in vitamin D metabolism. VDDR I is suggested to be a deficiency of the renal 25‐hydroxyvitamin D (25(OH)D)‐1α‐hydroxylase. Muscle weakness and rickets are the prominent clinical findings. A normal physiologic dose of 1α‐hydroxyvitamin D 3 and 1,25‐dihydroxyvitamin D 3 is sufficient to maintain remission of rickets in this disorder. VDDR II consists of a spectrum of intracellular vitamin D receptor (VDR) defects and is characterized by the early onset of severe rickets and associated alopecia. This can be attributed to mutations in the VDR gene. Massive doses of vitamin D analogs and calcium supplementation is usually required for the treatment; however, the response to therapy is sometimes variable.