Purine nucleoside phosphorylase deficiency (PNP-def) presenting with lymphopenia and developmental delay: successful correction with umbilical cord blood transplantation.

Purine nucleoside phosphorylase deficiency is a primary immunodeficiency syndrome characterized by the triad of recurrent infection, neurologic dysfunction, and autoimmunity. This patient presented atypically with few infections and normal T-cell function. Progressive lymphopenia, ataxia, and developmental delay led to diagnosis. Umbilical cord blood transplantation corrected the immunodeficiency.