Untargeted metabolomics analysis as a potential screening tool for 3-methylglutaconic aciduria syndromes

The 3-methylglutaconic aciduria (3-MGA-uria) syndromes comprise a heterogeneous group of inborn errors of metabolism defined biochemically by detectable elevation of 3-methylglutaconic acid (3-MGA) in the urine. In type 1 (or primary) 3-MGA-uria, distal defects in the leucine catabolism pathway directly cause this elevation. Secondary 3-MGA-uria syndromes, however, are unrelated to leucine metabolism-specific defects but share a common biochemical phenotype of elevated 3-MGA. It is currently thought that this accumulation is due to an underlying buildup of acetyl-CoA in the mitochondria from impaired function of the TCA cycle with ensuing formation of trans-3-methylglutaconyl CoA and its subsequent byproducts, including 3-MGA. In these disorders, urine 3-MGA levels are known to be fluctuant and at times undetectable by standard urine organic acid analysis (UOA), thereby reducing the utility of this biochemical screening method. Here, we retrospectively evaluated a cohort of nine patients with confirmed 3-MGA-uria syndromes. It was observed that UOA analysis obtained from three separate patients did not identify detectable 3-MGA levels. This inherent limitation highlights the need for a more sensitive clinical modality. Untargeted metabolomics profiling is a rapidly emerging technology that is being used to detect and characterize biochemical abnormalities in many inborn errors of metabolism. Untargeted metabolomics profiling performed on plasma samples in this cohort identified significant elevations of 3-MGA in all nine individuals. This high degree of clinical sensitivity demonstrates the promising potential for untargeted metabolomics analysis as both an effective biochemical screening tool for 3-MGA-uria syndromes and a functional method to assist with validation of genomic variants of uncertain significance in these disorders.