The present invention provides methods for assessing whether a subject is at risk of developing a neurological disorder, diagnosing or confirming whether a subject is afflicted with a neurological disorder, assessing whether PD has progressed in a subject afflicted with PD, assessing whether a neurological disorder is developing in a subject who has been identified as being at risk of developing the neurological disorder, assessing whether a subject afflicted with a neurological disorder is likely to benefit from a therapy, assessing whether a subject afflicted with a neurological disorder has benefited from a therapy, treating a subject afflicted with a neurological disorder, and prophylactically treating a subject who has been identified as being at risk of developing a neurological disorder. The present invention also provides epitopes, compounds and compositions relating to these methods.