APP and Alzheimer disease: Elevated expression levels of genes encoding the pathological hallmarks are not without precedent in other neurodegenerative diseases, such as duplication of the APP gene (amyloid precursor protein, causal for Alzheimer’s disease) (Sleegers et al., 2006), and locus triplication of α-synuclein (causal for Parkinson’s disease) (Singleton et al., 2003).