When targeted mice are bred with early embryonic Cre-expressing mice (EIIa-Cre, Hprt-Cre), ectoderm-specific Krt14-Cre, and limb mesenchyme-specific Prx-Cre mice, a variety of interesting phenotypes are observed that recapitulate various aspects of the human condition and prove that these mice provide a reliable animal model for human FDH. This evidence concerns the gene HPRT1 and focal dermal hypoplasia.