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Purine nucleoside phosphorylase deficiency, often called PNP-deficiency, is a rare autosomal recessive metabolic disorder which results in severe combined immunodeficiency.
The disorder is caused by a disruption of the purine nucleoside phosphorylase, a key enzyme in the purine salvage pathway.
This enzyme is required for purine degradation. Specifically, it catalyzes the conversion of inosine and guanosine to hypoxanthine. A deficiency of it leads to build up of elevated deoxy-GTP (dGTP) levels resulting in T-cell toxicity and deficiency.[1][2]
In contrast to adenosine deaminase deficiency (another deficiency of purine metabolism), there is minimal disruption to B cells.[3]
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. Lupus-erythematosis, autoimmune hemolytic anemia, and idiopathic thrombocytopenic purpura have been reported with PNP-deficiency.[4]
Neurological symptoms, such as developmental decline, hypotonia, and mental retardation have also been reported.
PNP-deficiency is extremely rare. Only 33 patients with the disorder in the United States have been documented.[4]
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