New ratio as a useful marker for early diagnosis of proximal urea cycle disorders.

Abstract Background and aims Proximal urea cycle disorders (PUCDs) are not included in most newborn screening programs due to the lack of adequate markers to monitor. Failure to alter citrulline and glutamine levels, the prognostic markers commonly used, can results in high false negative. Therefore, new biomarkers, prognostic of PUCDs, are strongly desirable. Materials and methods We used tandem mass spectrometry to analyze blood spot from PUCDs patients during their follow up in our referral center focusing on glutamine to glutamate (Gln/Glu) ratio. We reanalyzed the same specimens of three patients after two months and the specimen of a new patient with suspicious of PUCD disorder. Results Specimens of our patients shown a significant elevation of the ratio Gln/Glu compared to that of a healthy population (p  Conclusion Our preliminary results suggest that the Gln/Glu ratio could be a very useful diagnostic marker, more stable over time than glutamine, which could improve the performance in early PUCDs identification.