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PNP gene
Reviewed by Medicinsk Expert•Last updated: 2026-10-22•Gene

PNP gene

The PNP gene provides instructions for an enzyme that clears waste from DNA breakdown, playing a vital role in maintaining the health of the immune system.

Normal Function

The PNP gene provides instructions for making an enzyme called purine nucleoside phosphorylase. While found throughout the body, it is most active in lymphocytes—white blood cells that protect the body against bacteria and viruses. These cells are produced in lymphoid tissues, including the thymus and lymph nodes.

Purine nucleoside phosphorylase is a "housekeeping" enzyme that clears away waste molecules called deoxyinosine and deoxyguanosine, which are generated when DNA is broken down. It converts deoxyinosine to hypoxanthine and deoxyguanosine to guanine.

Health Conditions Related to Genetic Changes

Purine nucleoside phosphorylase deficiency

More than 35 PNP gene mutations have been identified in individuals with purine nucleoside phosphorylase deficiency. This immune system disorder leaves the body unable to fight foreign invaders, leading to life-threatening, repeated infections. Some individuals also experience neurological problems, such as intellectual disability or difficulty coordinating movements (ataxia).

  • Mechanism: Mutations reduce or eliminate enzyme activity, causing a buildup of waste molecules. This leads to the accumulation of deoxyguanosine triphosphate (dGTP) to levels that are toxic to lymphocytes.
  • T Cell Vulnerability: T cells, particularly immature ones in the thymus, are highly vulnerable to dGTP. The buildup damages these cells and triggers their self-destruction (apoptosis).
  • Neurological Impact: The shortage of lymphocytes causes immune vulnerability, while the buildup of dGTP is thought to damage brain cells, leading to neurological symptoms.

Genomic Location

The PNP gene is found on chromosome 14.

Frequently Asked Questions

Diagnosis typically involves a blood test measuring purine nucleoside phosphorylase enzyme activity. If low activity is found, a DNA sequencing panel for the PNP gene confirms the mutation. Prior to testing, patients should avoid taking medications that interfere with enzyme assays, such as certain antibiotics or antimetabolites, and fast for at least 8 hours if a metabolic panel is also ordered.
PNP deficiency is inherited in an autosomal recessive manner, meaning both parents must carry a mutation for a child to be affected. Carrier parents have a 25% chance of having an affected child with each pregnancy. Prenatal testing via chorionic villus sampling or amniocentesis can detect the mutation. Pregnancies in affected mothers may carry higher risks of miscarriage or fetal growth restriction, so close obstetric monitoring is recommended.===
Infants and toddlers may show recurrent ear, sinus, or respiratory infections that do not respond to standard antibiotics. They may also have unexplained fatigue, poor growth, or developmental delays such as delayed speech or motor milestones. A sudden drop in white blood cell count, especially lymphocytes, can also be an early red flag.
The mainstay of treatment is hematopoietic stem cell transplantation (HSCT), which can restore normal enzyme activity and immune function. Early HSCT, ideally before severe infections or neurological damage occur, offers the best chance for a normal lifespan. Supportive care includes prophylactic antibiotics, antiviral agents, and immunoglobulin replacement. Gene therapy trials are emerging but not yet standard.
Source: MedlinePlus, National Library of Medicine

MedlinePlus brings together authoritative health information from the National Library of Medicine (NLM), the National Institutes of Health (NIH), and other government agencies and health-related organizations.

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