MMP9 and mucopolysaccharidosis type 4A: The authors of [42] used liquid chromatography–tandem mass spectrometry (LC–MSMS) to measure the 4 disaccharides produced from GAGs in serum or plasma from 34 MPS IVA patients and identified 9 biomarkers that were significantly elevated in untreated MPS IVA patients: EGF, IL-1β, IL-6, TNF-α, MIP-1α, MMP-1, MMP-2, and MMP-9.