Diagnosis of immunodeficiency caused by a purine nucleoside phosphorylase defect by using tandem mass spectrometry on dried blood spots

J Allergy Clin Immunol. 2014 Jul;134(1):155-9. doi: 10.1016/j.jaci.2014.01.040. Epub 2014 Apr 24.

Abstract

Background: Purine nucleoside phosphorylase (PNP) deficiency is a rare form of autosomal recessive combined primary immunodeficiency caused by a enzyme defect leading to the accumulation of inosine, 2'-deoxy-inosine (dIno), guanosine, and 2'-deoxy-guanosine (dGuo) in all cells, especially lymphocytes. Treatments are available and curative for PNP deficiency, but their efficacy depends on the early approach. PNP-combined immunodeficiency complies with the criteria for inclusion in a newborn screening program.

Objective: This study evaluate whether mass spectrometry can identify metabolite abnormalities in dried blood spots (DBSs) from affected patients, with the final goal of individuating the disease at birth during routine newborn screening.

Methods: DBS samples from 9 patients with genetically confirmed PNP-combined immunodeficiency, 10,000 DBS samples from healthy newborns, and 240 DBSs from healthy donors of different age ranges were examined. Inosine, dIno, guanosine, and dGuo were tested by using tandem mass spectrometry (TMS). T-cell receptor excision circle (TREC) and kappa-deleting recombination excision circle (KREC) levels were evaluated by using quantitative RT-PCR only for the 2 patients (patients 8 and 9) whose neonatal DBSs were available.

Results: Mean levels of guanosine, inosine, dGuo, and dIno were 4.4, 133.3, 3.6, and 3.8 μmol/L, respectively, in affected patients. No indeterminate or false-positive results were found. In patient 8 TREC levels were borderline and KREC levels were abnormal; in patient 9 TRECs were undetectable, whereas KREC levels were normal.

Conclusion: TMS is a valid method for diagnosis of PNP deficiency on DBSs of affected patients at a negligible cost. TMS identifies newborns with PNP deficiency, whereas TREC or KREC measurement alone can fail.

Keywords: Purine nucleoside phosphorylase; T-cell receptor excision circle; delayed-onset; inherited disorder; late-onset; newborn screening; purine nucleoside phosphorylase–combined immunodeficiency; severe combined immunodeficiency; tandem mass spectrometry.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Adolescent
  • Child, Preschool
  • DNA Repair
  • Deoxyguanosine / analysis
  • Deoxyguanosine / metabolism
  • Dried Blood Spot Testing
  • Female
  • Guanosine / analysis
  • Guanosine / metabolism
  • Humans
  • Immunologic Deficiency Syndromes / diagnosis*
  • Immunologic Deficiency Syndromes / genetics
  • Immunologic Deficiency Syndromes / pathology
  • Infant
  • Infant, Newborn
  • Inosine / analogs & derivatives
  • Inosine / analysis
  • Inosine / metabolism
  • Lymphocytes / pathology
  • Male
  • Mutation*
  • Neonatal Screening
  • Primary Immunodeficiency Diseases
  • Purine-Nucleoside Phosphorylase / deficiency*
  • Purine-Nucleoside Phosphorylase / genetics*
  • Purine-Pyrimidine Metabolism, Inborn Errors / diagnosis*
  • Purine-Pyrimidine Metabolism, Inborn Errors / genetics
  • Purine-Pyrimidine Metabolism, Inborn Errors / pathology
  • Tandem Mass Spectrometry

Substances

  • Guanosine
  • Inosine
  • Purine-Nucleoside Phosphorylase
  • Deoxyguanosine
  • deoxyinosine

Supplementary concepts

  • Purine Nucleoside Phosphorylase Deficiency