FGF18 and hydrops fetalis: In conclusion, in HR overexpressing hairpoor mice, the HFSC quiescence is not maintained due to decreased HFSC niche signals including Fgf18, Bmp6, and Sfrp1. This leads to the telogen-to-anagen transition of HFs at the telogen phase, and proliferation of HF occurs through activation of the Wnt signaling in the hairpoor mouse (Fig. 6h).