Inborn errors of metabolism are rare diseases in which a single gene defect causes a clinically significant block in a metabolic pathway resulting either in an accumulation of substrate behind the block or a lack or deficiency of the product. Profiling metabolites in the pathway could allow for accurate and timely identification of patients who have these diseases and help physicians to devise effective treatment. Congenital disorders of glycosylation represent one of the largest groups of such metabolic disorders. In May 2019, Clinical Chemistry published a study on the development and validation of a plasma protein N-glycan assay using a flow injection-electrospray ionization-quadrupole time-of-flight mass spectrometry.