In addition to the symptoms associated with immunodeficiency, such as depletion of T-cells, decline of lymphocyte activity, and an abrupt proliferation of both benign and opportunistic infections—PNP-deficiency is often characterized by the development of autoimmune disorders.

[citation needed] The disorder is caused by a mutation of the purine nucleoside phosphorylase (PNP) gene, located at chromosome 14q13.1.

[citation needed] Diagnosis is based on the clinical examination and on laboratory findings showing leukopenia, severe lymphopenia with low CD3, CD4, and CD8 counts and variable B cell function and immunoglobulin levels.

[citation needed] Differential diagnosis includes aplastic anemias, SCID, severe combined immunodeficiency due to adenosine deaminase deficiency, ataxia-telangiectasia, and viral meningoencephalitis.

Few newborn screening programs also measure purine metabolites in dried[citation needed] Supportive treatment, including intravenous immunoglobulin therapy, prophylaxis for Pneumocystis carinii, and physical, occupational, and speech therapy, reduces the risk of infection and may encourage optimal neurologic development for patients.