BTG2 and Mobius syndrome: In fact, our recent study demonstrated that a new MB Shh-type mouse model, which lacks the MB-suppressor gene Tis21 (Ptch1+/-/Tis21-/-), develops MBs with high frequency in consequence of a defect of migration of the GCPs out of the EGL (Farioli-Vecchioli et al., 2007, 2012).