Deficiency-type rickets due to decreased sensitivity to vitamin D.

Rickets indistinguishable clinically and biochemically from that caused by vitamin D deficiency developed in an infant with a history of adequate vitamin D intake. Clinical and biochemical features of resistant rickets were not present. Although absorption of vitamin D was normal, as judged by serum vitamin D activity, alterations in calcium and phosphorus metabolism were similar to those of a D-deficient subject. When the infant was given 2,500 I.U. vitamin D daily, calcium and phosphorus balances became normal. It is concluded that this patient represents an instance of decreased sensitivity to vitamin D, with deficiency-type rickets occurring despite intake of recommended amounts of the vitamin.