An abnormal form of purine nucleoside phosphorylase in a family with a child with severe defective T-cell-and normal B-cell immunity.

1. Purine nucleoside phosphorylase and adenosine deaminase (ADA) were studied in normal red blood cells and lymphocytes and in the cells of a family with a child with a defective T-cell-and normal B-cell immunity. 2. In the propositus no purine nucleoside phosphorylase (NP) activity could be detected in her red cells and lymphocytes, while the ADA activity was somewhat increased. The NP activities of the father, mother and brother of the propositus are in the heterozygote range. The decreased activity of NP was not only found for the substrate inosine but also when guanosine or xanthosine were used as substrate. The mode of inheritance is autosomal recessive. 3. With starch gel electrophoresis no NP activity could be detected in the patient's haemolysate. The electrophoretic patterns of NP from the father, mother and brother of the patient seem to be the same as for normal NP with six bands of NP activity. 4. The nucleoside phosphorylases of the father, mother and brother of the patient were characterized by an increased KM for the substrate inosine, normal pH optimum and a decreased heat stability.