The hedgehog signaling pathway is constitutively active in cells of basal cell carcinoma and medulloblastoma. This activation is caused by the mutational inactivation or the deletion of the Patched-coding gene PTCH or by activating mutations in the gene SMO, which codes for Smoothened. Other mutations include inactivating mutations in the gene that codes for Sufu, which prevents Gli from entering the nucleus, as well as activating mutations in the genes coding for Gli1 and Gli2.

The hedgehog signaling pathway-Part 3:
The hedgehog signaling pathway-Part 1: