Assessment of methylcitrate and methylcitrate to citrate ratio in dried blood spots as biomarkers for inborn errors of propionate metabolism

Osama Y Al-Dirbashi,Claus-Dieter Langhans,Fatma Al-Jasmi,Jürgen G Okun,Aisha Al-Shamsi,Nahid Al Dhahouri,Zalikha Al Hammadi,Georg F Hoffmann,Majid Alfadhel,Khalid Al-Thihli,Jozef Hertecant

doi:10.1038/s41598-019-48885-9

Abstract

Deficiency of propionyl-CoA carboxylase causes propionic acidemia and deficiencies of methylmalonyl-CoA mutase or its cofactor adenosylcobalamin cause methylmalonic acidemia. These inherited disorders lead to pathological accumulation of propionyl-CoA which is converted in Krebs cycle to methylcitrate (MCA) in a reaction catalyzed by citrate synthase. In healthy individuals where no propionyl-CoA accumulation occurs, this enzyme drives the condensation of acetyl-CoA with oxaloacetate to produce citric acid (CA), a normal Krebs cycle intermediate. The competitive synthesis of CA and MCA through the same enzymatic mechanism implies that increase in MCA production is accompanied by decrease in CA levels. In this study, we assessed MCA concentration and the ratio of MCA/CA as plausible markers for propionic and methylmalonic acidemias. We measured MCA and CA in dried blood spots using liquid chromatography tandem mass spectrometry. The reference ranges of MCA, CA and MCA/CA in 123 healthy individuals were ≤0.63 µmol/L, 36.6–126.4 µmol/L and 0.0019–0.0074, respectively. In patients with propionic and methylmalnic acidemias (n = 7), MCA concentration ranged between 1.0–12.0 µmol/L whereas MCA/CA was between 0.012–0.279. This is the first report to describe the potential role of MCA and MCA/CA in dried blood spots as diagnostic and monitoring biomarkers for inherited disorders of propionyl-CoA metabolism.

Highlights

Propionic acidemia (PA) and methylmalonic acidemia (MMA) are inborn errors of propionyl-CoA metabolism caused by defects in enzymes required for correct catabolism of branched-chain amino acids, odd chain fatty acids and cholesterol[1]
Blood gases and calculated anion gap are non-specific markers that occur in other disorders[1,3,6], a number of complications occur in PA and MMA patients despite these biomarkers being within therapeutic targets
The challenge in managing PA patients is confounded by the lack of a reliable biomarker for monitoring and prognostication

Summary

Introduction

Propionic acidemia (PA) and methylmalonic acidemia (MMA) are inborn errors of propionyl-CoA metabolism caused by defects in enzymes required for correct catabolism of branched-chain amino acids, odd chain fatty acids and cholesterol[1]. MMA is a more etiologically heterogeneous disorder that can present as isolated MMA or in combination with homocystinuria. The former is caused by genetic defects in methylmalonyl-CoA mutase or its cofactor adenosylcobalamin. In MMA, accumulation of methylmalonic acid together with elevated glycine, propionylcarnitine, 3-hydroxypropionic acid and MCA is diagnostic[1,3,11]. We used liquid chromatography tandem mass spectrometry (LC-MS/MS) to simultaneously determine CA and MCA in DBS in the same analytical run This allowed for the calculation of MCA/CA ratio, a novel biomarker that may potentially apply for all disorders of propionate metabolism.

Methods

Results

Conclusion