Unfortunately, after decades of research and hundreds of unsuccessful phase III clinical trials, it's clear that the pharmacological industry and a cohort of academic laboratories are unable to create drugs that slow significantly the progression of neurodegenerative diseases.
Some courageous scientists interrogate basic hypotheses or design longer, more complex better clinical trials. For example, Alzheimer's disease can't seriously be attributed to any molecular dysfunction, as it would mean that a lot of cerebral functions would be affected, not only memory issues, and anyway, memory issues in Alzheimer's are much more complex than described in textbooks: They did not simply vanish: The patient looks to be living today in the context of the past. Sometimes the patient can discuss simultaneously at two levels: In the context of the past (when they were infants) and in the context of today.
Others are currently busy breaking the thermometer. If the clinical diagnosis makes it impossible to validate current clinical trials, then change the way success is defined: Abandon clinical criteria and use molecular criteria. They did it recently for Alzheimer's disease and now they propose it for Parkinson's disease..
The immediate consequence will be a flurry of successful clinical trials, even if patients get no improvements, as they did for Aducanumab.
There will also be false positives, people will be diagnosed sick because of the presence of a molecule but without any clinical signs.