Abstract: The present disclosure relates to methods and compositions for elevating and stabilizing retromer protein for treating and/or preventing neurodegenerative diseases and disorders including Alzheimer's disease and Parkinson's disease, where retromer dysfunction and/or endosomal trafficking dysfunction is involved and/or implicated in the disease or disorder. The methods include the use of agents to elevate and stabilize specific retromer depending upon the neurodegenerative disease or disorder being treated. The method can also include the use of one or more biomarkers to detect and/or identify whether retromer dysfunction and/or endosomal trafficking dysfunction is involved and/or implicated in the disease or disorder.