Neurofilament light (NfL)—a protein released upon neuroaxonal injury into the cerebrospinal fluid (CSF) and plasma—has been identified as a promising biomarker for diagnostic and prognostic purposes, as it corresponds with neuroaxonal injury and degeneration in other neurodegenerative diseases such as pediatric multiple sclerosis, acute disseminated encephalomyelitis, spinal muscular atrophy and perinatal asphyxia [17,18,19]. Here, NEFL is linked to proximal spinal muscular atrophy.