Our assessment of TP stability in blood stored at room temperature supports this explanation because many of the samples received for TP measurements in suspected MNGIE patients were collected with EDTA.
Only MNGIE patients have increased plasma concentrations of both dUrd (>5 [micro]mol/L) and dThd (>3 [micro]mol/L), whereas mutation carriers with partially reduced TP activity have no detectable pyrimidine nucleosides (<0.05 [micro]mol/L) in plasma.
On the basis of our results, we propose an algorithm using measurements of dThd and dUrd in plasma and TP activity in buffy coat to diagnose MNGIE. Fig.
In cases with moderately increased plasma nucleoside concentrations, we propose measurement of buffy coat TP activity to confirm the diagnosis of MNGIE. In this situation, a severe loss of TP function is considered diagnostic.
In conclusion, the algorithm for biochemical screening of possible MNGIE patients proposed here provides a simple and practical method to definitively confirm the diagnosis.
Mitochondrial neurogastrointestinal encephalomyopathy (MNGIE): clinical, biochemical, and genetic features of an autosomal recessive mitochondrial disorder.
Phenotypic variability in a Spanish family with MNGIE. Neurology 2002;59:455-7.
MNGIE: an autosomal recessive disorder due to thymidine phosphorylase mutations.
Four novel thymidine phosphorylase gene mutations in mitochondrial neurogastrointestinal encephalomyopathy syndrome (MNGIE) patients.
Partial depletion and multiple deletions of muscle mtDNA in familial MNGIE syndrome.
MNGIE neuropathy: 5 cases mimicking chronic inflammatory demyelinating polyneuropathy.
 Nonstandard abbreviations: MNGIE, mitochondrial neurogastrointestinal encephalomyopathy; TP, thymidine phosphorylase; dThd, thymidine; and dUrd, deoxyuridine.