MMP9 and mucopolysaccharidosis type 4A: Eight biomarkers were significantly elevated in untreated MPS IVA patients as well: EGF, IL-1β, IL-6, MIP-1α, MMP-9, HSNS, mono-sulfated KS, and di-sulfated KS, and four biomarkers were elevated in MPS IVA patients under ERT: IL-6, TNF-α, mono-sulfated KS, and di-sulfated KS.