Case report 668. Carbonic anhydrase II deficiency syndrome (osteopetrosis associated with renal tubular acidosis and cerebral calcification).

A 4-month-old infant with bronchiolitis was found to have hyperdense bones on chest roentgenograms. The diagnosis of osteopetrosis was demonstrated by generalized increased radiological bone density and by a bone biopsy showing persistence of calcified cartilage. The infant also had a mixed proximal and distal renal tubular acidosis requiring as much as 12 mEq/kg per day of sodium bicarbonate. Measurement of his erythrocyte carbonic anhydrase activity revealed a deficiency of CA II. His parents showed values of CA activity that were intermediate between controls and the proband. Thus, this is a patient with the CA II deficiency syndrome; he is the youngest reported case without any family history of osteopetrosis to be diagnosed initially on the basis of his radiographic features.