Understanding the transition between these different stages is a major challenge, especially in view of the recent development of disease modifying therapy.<h4>Methods</h4>This is an observational study, CSF levels of Tau, pTau181, pTau217, Aβ38/40/42, sAPPα/β, BACE1 and neurogranin were measured in the BALTAZAR cohort of cognitively impaired patients and in the Alzheimer's Disease Neuroimaging Initiative (ADNI). The gene discussed is BACE1; the disease is Alzheimer disease.