Purine nucleoside phosphorylase deficiency

Purine nucleoside phosphorylase deficiency
Classification and external resources
ICD-10	D81.5
ICD-9-CM	277.2
OMIM	613179
DiseasesDB	11044
eMedicine	ped/1957
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Purine nucleoside phosphorylase deficiency, often called PNP-deficiency, is a rare autosomal recessive metabolic disorder which results in immunodeficiency.

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 erythematosus, autoimmune hemolytic anemia, and idiopathic thrombocytopenic purpura have been reported with PNP-deficiency.

Neurological symptoms, such as developmental decline, hypotonia, and mental retardation have also been reported.

The disorder is caused by a mutation of the purine nucleoside phosphorylase (PNP) gene, located at chromosome 14q13.1. PNP is a key enzyme in the purine salvage pathway, and is required for purine degradation. Specifically, it catalyzes the conversion of inosine to hypoxanthine and guanosine to guanine (both guanine and hypoxanthine will be made into xanthine which will then become uric acid). A deficiency of it leads to buildup of elevated deoxy-GTP (dGTP) levels resulting in T-cell toxicity and deficiency. In contrast to adenosine deaminase deficiency (another deficiency of purine metabolism), there is minimal disruption to B cells.

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