KLF4 and popliteal pterygium syndrome: The 32 identified genes include Ripk4, a regulator of periderm development in the epidermal epithelium that has been implicated in human popliteal pterygium syndromes [69, 70], Klf4, a classical stem cell factor that also regulates epidermal periderm development [76–79], Tmeff2, which was previously identified as having a role in bat limb elongation [80], and Adamts5, a metalloprotease that has been implicated in interdigitation [81].