Purine nucleoside phosphorylase (PNP) deficiency catalyses the conversion of the purine nucleosides inosine, deoxyinosine, guanosine and deoxyguanosine to the respective bases. The enzyme is assayed in red cell lysates using inosine as the substrate with products of the reaction separated from substrate by HPLC.
Inherited severe combined immunodeficiency. Children typically present with recurrent infections due to absent T-cell immunity. There may be B-cell dysfunction leading to autoimmunity. Neurological abnormalities are present in about 50% of patients. Uric acid in plasma may be low, but not always. The disorder is autosomal recessive.