APP and Alzheimer disease: Somatic mutations have been identified in the α-synuclein gene, where a recombination mechanism resulted in somatic variants of the amyloid precursor protein gene causing AD, with the α-synuclein toxic gain of function effects resulting in PD and multiple system atrophy, single nucleotide variants affecting tau phosphorylation leading to AD and single nucleotide variants in DNA repair genes causing motor neuron disease [41,43].