Antibodies and fragments thereof have high affinity for human α-
synuclein protofibrils and low binding of α-
synuclein monomers, wherein the antibodies or fragments have specified 
Complementarity Determining Region (CDR) sequences. Compositions comprise such an 
antibody or fragment and methods of detecting α-
synuclein protofibrils use such an 
antibody or fragment. In further embodiments, methods of preventing, delaying onset of or treating a neurodegenerative disorder with α-synuclein 
pathology comprise administering such an 
antibody or fragment, and such an antibody or fragment is used in the manufacture of a pharmaceutical composition for treatment of a neurodegenerative disorder with α-synuclein 
pathology. Such an antibody or fragment is used in the diagnosis or monitoring of the development of a neurodegenerative disorder with α-synuclein 
pathology, and in methods for reducing or inhibiting α-synuclein aggregation by administration of such an antibody or fragment.