For years, neurology has assumed that clinical observations will match nicely onto something we can measure in biology. This led to assumptions that Alzheimer’s, Parkinson’s, and other diseases of brain aging each have a unifying biology. However, every attempt to target such biology has failed.
In reality, each of these diseases is made of a range of abnormal biological pathways. To treat individuals diagnosed with a degenerative brain disease, we must target only those who have evidence of the abnormal biological pathway against which a treatment is designed.