Mutations in the human homologue of Drosophila patched (PTCH) in basal cell carcinomas and the Gorlin syndrome: different in vivo mechanisms of PTCH inactivation.

The nevoid basal cell carcinoma (Gorlin) syndrome (NBCCS) is an autosomal dominant disorder characterized by multiple developmental defects and cancer susceptibility, in particular to basal cell carcinoma. The human homologue of Drosophila patched (PTCH) was recently identified, mapped to the NBCCS locus on chromosome 9q22.3, and found mutated in patients with NBCCS and also in sporadic basal cell carcinomas. Here we show germ-line PTCH mutations in three families with NBCCS. We demonstrate that a germ-line PTCH frameshift deletion in one patient with NBCCS was accompanied by loss of the normal copy of PTCH in a tumor developed in the same patient. Another basal cell carcinoma from this patient did not show the loss of the normal copy of PTCH, instead a missense mutation in a highly conserved residue was identified in the nondeleted allele, illustrating two different mechanisms of PTCH inactivation in different tumors derived from the same NBCCS patient. We also show somatic PTCH mutations in 4 basal cell carcinomas identified by analyzing 18 non-NBCCS patients with sporadic tumors. These data provide further support for PTCH as an important tumor suppressor gene in the development of the most common human cancer.