We summarize here lessons learned from studies on skeletal and extra-skeletal functions of
vitamin D in hereditary 1, 25-dihydroxyvitamin D–resistant rickets (HVDRR) patients with a
mutant, nonfunctioning vitamin D receptor (VDR). During childhood, HVDRR patients are
dependent on intestinal VDR, demonstrate low intestinal fraction calcium absorption, and
have a bone calcium accretion rate that leads to hypocalcemia and rickets. After puberty,
there is recovery in intestinal calcium absorption and in bone calcium accretion and …