GDF2 and Alzheimer disease: Subsequent evidence revealed that BMP9 was critical for the differentiation, maturation, and phenotype maintenance of cholinergic neurons (López-Coviella et al., 2000, 2005; Schnitzler et al., 2010), suggesting that BMP9 may exert beneficial effects in the treatment of diseases associated with the profound degeneration of cholinergic systems, such as AD (Whitehouse et al., 1982; Grothe et al., 2010).