Hypocalcemic vitamin D-resistant rickets (Orphanet_93160, an Orphanet rare-disease nomenclature entry) (HVDRR) is a hereditary disorder of vitamin D action characterized by hypocalcemia, severe rickets and in many cases alopecia. Also known as: HVDRR, Hereditary vitamin D-resistant rickets, VDDR II, VDRR II, Vitamin D-dependent rickets type II, Vitamin D-resistant rickets type II.