Purine Nucleoside Phosphorylase

Alternative Names

  • PNP
  • Nucleoside Phosphorylase
  • NP
  • Purine-Nucleoside:Orthophosphate Ribosyltransferase
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OMIM Number

164050

Gene Map Locus
14q11.2

Description

The PNP gene gives instruction for making an enzyme that catalyzes the phosphorolytic breakdown of the N-glycosidic bond in the beta-(deoxy)ribonucleoside molecules.  This enzyme contains three identical subunits and is found throughout the body but is most active in the lymphocytes.  Defects in this enzyme are the cause of purine nucleoside phosphorylase deficiency, a disorder characterized by profound T cell deficiency, recurrent and opportunistic infections, progressive neurologic manifestations, autoimmunity disorders and malignancy.

 

Molecular Genetics

The PNP gene was mapped to the long arm of chromosome 14 at position 11.2.  It has six coding exons spanning about 9 kb within the genomic DNA.  The encoded protein consists of 289 amino acids with a molecular weight of 32 kDa.  More than 27 different mutations in this gene have been identified in patients with purine nucleoside phosphorylase deficiency.  These mutations lead to the buildup of deoxyguanosine triphosphate (dGTP) that is toxic to lymphocytes.

 

Epidemiology in the Arab World

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Other Reports

Saudi Arabia

Al-Saud et al. (2009) described a two-year-old Arab boy born to first cousin parents with purine nucleoside phosphorylase deficiency.  He was the eighth child, his two older sisters died from recurrent infections.  The first sister died at the age of 3 years without definite diagnosis, while the second sister was diagnosed with PNP deficiency and also died at the age of 3 years.  He had two episodes of infections: first, a chest infection at the age of 2 months, and second, an ear infection at the age of 1 year.  He had developmental delays, was not able to sit or walk at the age of 1.5 years.  Performing sequence analysis for the PNP gene showed a novel homozygous missense mutation (c.487T>C), that resulted in an amino acid substitution (S163P) in the mature PNP enzyme this lead to a complete loss of PNP function.

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