We further compared longitudinal trajectories of serum BSN (sBSN) and serum neurofilament light chain (sNfL) in a cohort of people with primary progressive MS (PPMS) (n = 26) using linear mixed-effects models.<h4>Findings</h4>The synaptoneurosome screen revealed reduced levels of several presynaptic proteins, including BSN, in the cortex of EAE mice. Here, BSN is linked to primary progressive multiple sclerosis.