NEFL and mucopolysaccharidosis: Serum neurofilament light-chain (NfL) levels were substantially decreased compared to baseline (median: 73%, p < 0.001 for longitudinal comparison) in IA patients, whereas they were rather unaffected by MPS treatment (median: 105%; p = 0.081 for longitudinal comparison; p = 0.004 for comparison of MPS and IA), although it is unknown whether NfL is retained by IA columns.