Ptch2 plays redundant roles during embryogenesis (Motoyama et al., 1998b; Zhulyn et al., 2015), and the phenotypes of Ptch2 mutants are manifested at postnatal stages; the mutation causes alopecia (hair loss) and epidermal hyperplasia (Nieuwenhuis et al., 2006). Here, PTCH2 is linked to alopecia.