[QUOTE=soccertese;1009361]
Others argue the failures have a simpler explanation — there’s nothing left to rescue; that trial patients’ nigrostriatal damage is too advanced to reverse.

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Which all leads back to my earlier posts that the NIH study and other studies may be using patients to far advanced. Its the reason why the study samples must include early stage patients if we are to get some answer as to the efficacy of these growth factor drugs. Even then it may be too late. Basically, these studies may be guaranteeing failure by insisting on a sample of late stage patients.

To quoted from the article you linked:

“Neurotrophic factors will only work if you start super early. If you wait until the formal diagnosis has been made, there's often a lot of destruction, and you can't really hope to reverse that.” British neuropathologist Chris Hawkes says by the time a patient gets a firm diagnosis of PD, “the pathology is far more advanced than you’d think…. And to put it crudely, the brain is well and truly pickled.”