PNP is a member of the PNP/MTAP phosphorylase family of proteins. PNP catalyzes the reversible phosphorolysis of ribonucleosides and 2’-deoxyribonucleosides with specificity for guanine， hypoxanthine and their analogs. PNP deficiency is a rare autosomal recessive genetic disease linked to a severe defect in T-lymphocyte function and neurologic disorder in children， comprising four percent of combined immunodeficiency cases.
