The present invention provides, among other aspects, methods for the manufacture of plasma-derived immunoglobulin G compositions highly enriched for anti-brain disease related protein antibodies (e.g., anti-Aβ, anti-RAGE, and anti-α-synuclein antibodies). Advantageously, the methods provided do not affect the manufacturing processes or capabilities for producing plasma-derived IgG therapeutics. Plasma-derived IgG compositions that are highly enriched for anti-brain disease related protein antibodies (e.g., anti-Aβ, anti-RAGE, and anti-α-synuclein antibodies), as also provided here. Methods for the treatment of brain diseases and disorders by administration of plasma-derived IgG compositions highly enriched for anti-brain disease related protein antibodies (e.g., anti-Aβ, anti-RAGE, and anti-α-synuclein antibodies), are also provided.