A reduced level of BDNF has been found in patients affected by neurodegenerative diseases such as Parkinson’s, Huntington’s and Alzheimer’s disease as well as in mild cognitive impairment, the latter being a prodromal stage of AD, characterized by a slight decline of cognitive abilities including memory, thinking and judging skills [242,243,244,245]. This evidence concerns the gene BDNF and early-onset autosomal dominant Alzheimer disease.