AXIN2 and Familial exudative vitreoretinopathy: Due to the critical role of Wnt signaling in cell growth and normal stem cell progression, genetic alteration of the components within this pathway including the lost-of-function mutations/deletions of APC, LRP5, AXIN2 promotes different diseases, including bone density defects (LRP5, Wnt1) (Van Wesenbeeck et al., 2003), familial exudative vitreoretinopathy (FZD4) (Toomes et al., 2004) and colon cancer (APC, AXIN2) (Morin et al., 1997; Lammi et al., 2004).