The neuroprotective effects of NPY include interaction with brain-derived trophic factors; for example, in Alzheimer's disease (AD), Aβ25–35 reduces intracellular nerve growth factor (NGF) and brain-derived neurotrophic factor (BDNF), whereas NPY fully restores the levels of these growth factors [82]. This evidence concerns the gene NPY and early-onset autosomal dominant Alzheimer disease.