IDS and mucopolysaccharidosis type 2: Notably, the intrathecal administration of idursulfase to patients with MPS II or recombinant sulfamidase to patients with MPS IIIA decreased GAG/HS concentrations in the CSF but was hardly effective for cognitive function in most cases [146,147,148,149,150], casting doubt on the use of CSF HS as a surrogate biomarker for brain HS deposition and neurological dysfunction.