PTCH1 and hydrops fetalis: BCC develops upon supra-physiological Hh-pathway activation in epithelial cells, with the most prevalent mutations in the inhibitory Hh-receptor gene Ptch1. Like HF formation, Hh-driven BCC is characterized by active Wnt/b-catenin signaling (Yang et al., 2008), and early epithelial BCC buds express typical HF-lineage markers even if they don't originate from HFs (Kasper et al., 2011; Yang et al., 2008; Youssef et al., 2012).