In 1961, Prader et al. (1961) reported on a new form of vitamin D resistant rickets, which differed from the classic hypophosphatemic type (Albright et al. 1937) by its early onset (within the first year of life), the development of severe hypocalcemia with tetany, moderate hypophosphatemia and hyperaminoaciduria both reflecting secondary hyperparathyroidism, enamel hypoplasia and the complete correction of all clinical and biochemical evidence of rickets (including stunted growth rate) with high daily doses of vitamin D. In the initial report identifying this hereditary form of pseudo-vitamin D deficiency rickets (PDDR), transmission was reported to be autosomal dominant. Later, recessive inheritance was established (Fanconi & Prader 1969). In view of the fact that to maintain health, intake of vitamin D had to be consistently in vast excess of the recommended daily allowance (400 IU), the term 'vitamin D dependency' (VDD) was proposed to describe the new syndrome (Scriver 1970).