To our knowledge, this is the first study exploring the global concentrations of plasma IgM, total IgG, and IgG1-4 subclasses along with subclass autoantibodies toward conventional neuropathological amyloidogenic proteins i.e., α-syn, pSer129-α-syn, β-syn, γ-syn, Aβ and tau protein, in MSA and PD patients compared to a control group. The gene discussed is CD40LG; the disease is multiple system atrophy.