APP and Alzheimer disease: For instance, certain pathogenic mutations in the gene coding for the amyloid‐β precursor protein (APP) cause AD, in the α‐synuclein gene are related to PD, in huntingtin are related to Huntington's disease (HD) or in microtubule‐associated protein tau are associated with frontotemporal dementia (FTD) with parkinsonism (Bertram & Tanzi, 2005).