First, it is well-established that mosaic mutations can be passed on to offspring as germline heterozygous disease, for example, epidermal naevi with keratin 1 gene K1 and keratin 10 gene K10 mutations passed on as epidermolytic ichthyosis (Nomura et al., 2001; Paller et al., 1994) or mosaic NF1 being passed down as germline NF1 (Rasmussen et al., 1998; Tinschert et al., 2000; Zlotogora, 1993). The gene discussed is KRT10; the disease is epidermolytic ichthyosis.