The monoaminergic neurons show degenerative changes in the early stages of AD, and it has previously been shown that the progression of Aβ deposition is accompanied by a progressive loss of monoaminergic afferents to the forebrain in APP/PS1 mice, and that axonal degeneration is probably due to the atrophy or loss of monoaminergic neurons [173]. This evidence concerns the gene APP and Alzheimer disease.