Hypocalcemic vitamin D-dependent rickets (Orphanet_289157, an Orphanet rare-disease nomenclature identifier) (VDDR-I) is an early-onset hereditary vitamin D metabolism disorder characterized by severe hypocalcemia leading to osteomalacia and rachitic bone deformations, and moderate hypophosphatemia. Also known as: 1-alpha-hydroxylase deficiency, PDDRI, Pseudovitamin D-deficient rickets, VDDI, VDDR-I, Vitamin D dependent rickets type I, Vitamin D-dependency type I.