In a mixed group of 58 CBS/PSP patients, Real-Time Quaking Induced Conversion (RT-QuIC) analyses documented no seeding activity for a-syn and the combination of a-syn RT-QuIC with CSF NfL levels discriminated 116 PD patients from PSP/CBS with an accuracy of 99% (p < 0.01). Here, NEFL is linked to Parkinson disease.