Purine nucleoside phosphorylase (PNP) deficiency is a primary immunodeficiency syndrome characterized by recurrent infections, neurologic symptoms, and autoimmune disorders. PNP deficiency causes a shortage of white blood cells called T cells that help fight infection. Some people with this condition develop neurologic symptoms, such as spasticity, ataxia, developmental delay, or intellectual disability. In addition, PNP deficiency is associated with increased risk of autoimmune disorders, such as autoimmune hemolytic anemia, idiopathic thrombocytopenia (ITP), autoimmune neutropenia, thyroiditis, and lupus. PNP deficiency is a autosomal recessive disorder caused by mutations in the PNP gene. Treatment with bone marrow transplantation can improve the immune system problems associated with this condition, but does not improve the neurologic symptoms. Source: Genetic and Rare Diseases Information Center (GARD), supported by ORDR-NCATS and NHGRI.