PTCH1 (patched homolog 1) is a twelve-pass transmembrane protein that acts as a receptor of Hedgehog signaling pathway (PMID: 8906794). Hedgehog pathway plays a critical role in embryonic development and tissue homeostasis, and its dysregulation has been implicated in many human diseases including congenital disorder and cancer (PMID: 23719536; 23532857). In the absence of Hedgehog proteins (SHH, IHH and DHH in humans), PTCH1 represses the activity of Smoothened (SMO). Binding of Hedgehog proteins to PTCH1 inhibits the repression of SMO, resulting in the activation of downstream targets through the Gli transcriptional effectors (PMID: 23719536; 17139287). The gene of PTCH1 is considered to be a tumor suppressor gene. Mutations of this gene have been associated with basal cell nevus syndrome, esophageal squamous cell carcinoma, trichoepitheliomas, transitional cell carcinomas of the bladder, as well as holoprosencephaly.