NEFL and X-linked adrenoleukodystrophy: In other diseases, it is known that normalization or close-to-baseline decrease in NfL is possible with treatment, but the time lag between treatment initiation and time to stable decline of NfL appears highly variable among diseases and treatment modalities when considering antisense oligonucleotide, nusinersen-treated peadiatric spinal muscular atrophy versus treated adolescents or adults,86–88 heamatopoietic stem cell–transplanted X-linked adrenoleukodystrophy,89 antiviral-treated adult HIV dementia,90–92 or monoclonal antibody-treated adult multiple sclerosis.32,93