The elevated ApoB levels in sALS CSF compared with HC and multiple sclerosis CSF were validated by ELISA, and we additionally detected low ApoB levels in SOD1, C9 and TARDBP CSF (Supplementary Fig. 3A), consistent with the absence of motor deficits and reduced extent or lack of ALS-like pathology in C9 and TARDBP CSF-injected mice, and SOD1 CSF-injected mice, respectively. Here, C9 is linked to amyotrophic lateral sclerosis.