We analysed CSF candidate biomarkers for degenerative CNS processes (namely phosphorylated heavy chain (pNf‐H), light‐chain neurofilaments (NfL), total tau protein (T‐Tau), neurogranin, β‐secretase BACE‐1 and alpha‐synuclein) in 193 CSF samples of 44 paediatric SMA types 1, 2 and 3 patients before and under nusinersen treatment and related them to standardized clinical outcome scores in a single‐centre pilot study. The gene discussed is BACE1; the disease is proximal spinal muscular atrophy.