Abstract: The invention provides the art with a powerful diagnostic method of distinguishing relapse-remitting MS subjects from progressive MS subjects, based on the measurement of serum concentrations of N-acetylglucosamine (GlcNAc,), for the first time enabling rapid diagnosis of the progressive form of MS. GlcNAc serum concentration can also be used to assess neurodegenerative status and MS progression in subjects suffering from MS or other neurological conditions. The methods of the invention also allow for the identification of new therapeutics for MS and other neurological conditions and also enables the personalized efficacy assessment of a potential therapy for an MS subject.