The Hedgehog (HH) signaling pathway is involved in patterning and development of a variety of organ systems, including the nervous system, the skeletal system, the craniofacial structures, and the gastrointestinal tract. Recent evidence also implicates this signaling pathway in the postembryonic regulation of stem-cell number in epithelia and blood. The family of HH proteins consists of at least three different members, i.e., sonic HH (SHH), Indian HH (IHH), and desert HH (DHH). SHH is the most broadly expressed member of this family and is probably responsible for the major effects of this signaling pathway. The HH signal is received and transduced via a specific receptor complex composed of patched (PTCH) and smoothened (SMOH) transmembrane proteins. Abnormalities in this signaling cascade have been found in various developmental pathologies and neoplasms such as basal cell carcinoma. The abnormalities are associated with congenital or sporadic genetic alteration affecting function of different components of the HH signaling pathway, including SHH, PTCH, SMOH and GLI proteins.

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