Currently available treatments for neurodegenerative diseases are exclusively palliative. In Alzheimer's disease (AD) they are focused on the cholinergic deficit and alterations in glutamate function related to neurotoxicity. Finding drugs that can attenuate or reverse neurodegenerative disease progression is challenging in the absence of a complete understanding of the underlying causes. Biomarkers represent any measure that can be used to indicate the presence of a disease state. Biomarkers are critical both for making an accurate diagnosis of each of the neurodegenerative diseases and for assessing their status and response to treatment. They are crucial for clinical trials from their initial design, to patient recruitment, to establishing objective end points. Neurodegenerative disease-associated genes continue to be identified at an ever-increasing rate using genome-wide association studies (GWAS) in cohorts of affected individuals. A large number of candidate genes and loci identified for neurodegenerative diseases, for example, in excess of 120 for AD.