The biochemical features of two families with purine nucleoside phosphorylase deficiency are compared. Laboratory studies and an evaluation of kinetic and physical properties of erythrocyte purine nucleoside phosphorylase give evidence that a) the degree of abnormality in uric acid and nucleoside concentrations in plasma and urine reflect the severity of the enzymatic deficiency and b) structural alterations of the mutant enzymes result from structural gene mutations and demonstrate genetic heterogeneity in the disease purine nucleoside phosphorylase deficiency.Purine nucleotide degradation is an intricately regulated enzymatic sequence. The relevance of these enzyme reactions to clinical disorders of immune function was first noted when adenosine deaminase deficiency was found associated with combined B-and T-cell dysfunction (1). The observations that purine nucleoside phosphorylase deficiency occurs with cellular immune dysfunction (2-8) and ecto-5'-nucleotidase Submitted for publication November 2, 1978; accepted January 9, 1979. deficiency occurs with agammaglobulinemia (9) further emphasized this relationship.Purine nucleoside phosphorylase is an integral part of the nucleotide degradation pathway. A deficiency of this enzyme blocks this reaction sequence and results in an immune disorder (2-8). The enzyme deficiency and the concomitant clinical syndrome may result from structural gene mutations (10,ll). We have examined the clinical features and biochemical properties of the enzyme from 3 patients in two families with purine nucleoside phosphorylase deficiency. The data indicate that the laboratory changes observed in the patients reflect the degree of enzyme deficiency and that altered properties of the deficient enzymes provide evidence for a structural gene alteration and genetic heterogeneity in the disease purine nucleoside phosphorylase deficiency.
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