FGF9 and Huntington disease: A number of other growth factors have been proposed for HD treatment, including BDNF, ciliary neurotrophic factor, and fibroblast growth factor 9 (Anderson et al, 1996; Emerich et al, 1997; Mittoux et al, 2000; Zuccato & Cattaneo, 2007; Xie et al, 2010; Yusuf et al, 2018).