Purine nucleoside phosphorylase deficiency associated with selective cellular immunodeficiency.

We studied a 15-month-old girl who had normal T-cell and B-cell immunity at birth, after which a gradual decrease in T-cell immunity developed. This selective cellular immunodeficiency was inherited as an autosomal recessive trait: two older sisters had the same immunodeficiency. Adenosine deaminase activity was present in erythrocytes and lymphocytes of the patient, parents and a healthy brother. Purine nucleoside phosphorylase activity was not found in the patient's erythrocytes and lymphocytes (the parents and brother had intermediate values, indicating that the enzyme deficiency too was inherited as an autosomal recessive trait). Analysis of serum and urine from the patient and of serum from her two deceased sisters showed high levels of inosine and guanosine in addition to hypouricemia and hypouricosuria. The bone marrow was megaloblastic, and the blood hypochromic microcytic. The patient had spastic tetraparesis. Intoxication of the T lymphocytes after birth by metabolic products may explain the progressive cellular immunodeficiency.