Purine nucleoside phosphorylase (PNP)-deficiency is a primary immune deficiency with PNP gene mutation, clinically characterized by a progressive combined immunodeficiency, neurologic symptoms including developmental delay, spasticity, ataxia, and pyramidal signs, and autoimmune manifestations including hemolytic anemia (114–118). Here, PNP is linked to hyperinsulinemic hypoglycemia, familial, 4.