The nevoid basal cell carcinoma syndrome is an autosomal dominant disorder characterized by multiple cutaneous basal cell carcinomas, jaw keratocysts and a variety of other tumours, and developmental abnormalities. Recently, this syndrome was shown to result from germ line mutations in human patched(PTC) gene, which encodes a membrane receptor and functions as an important developmental regulator and a tumour suppressor. Haploinsufficiency for the PTC locus is likely to give rise to developmental abnormalities characterized by symmetrical defects and malformed spine and ribs. Postnatal loss of the normal PTC allele leads to multiple basal cell carcinomas and other cancers. PTC mutations and loss of the remaining wild-type allele have also been identified in sporadic basal cell carcinomas and meduloblastomas.