College of American Pathologists (CAP)/American College of Medical Genetics and Genomics (ACMG) proficiency testing for urinary glycosaminoglycan analysis: A summary of performance

Based on the data reviewed, best patient care for those at risk of an MPS is achieved by a combination of total GAG analysis and GAG fractionation. Development of liquid-chromatography-tandem-mass-spectrometry-based methods for quantitative, differentiated GAG analysis or disease-specific GAG-derived nonreducing end oligosaccharide fragments in combination with multiplexed lysosomal enzyme assays will likely improve diagnostic accuracy. The decline of laboratories participating in PT is concerning because MPS are increasingly included in newborn screening programs and urinary GAGs can be used to monitor the effectiveness of new therapies.