MAPT and Alzheimer disease: Several CSF biomarkers have already been identified for various diseases and are used in research, clinical trials and clinical practice, including CSF-specific IgG immunoglobulins in multiple sclerosis, the 14-3-3 protein in Creutzfeld-Jakob's disease (CJD), the tau protein, and the β-amyloid peptides in Alzheimer's disease (AD).