Linear basal cell nevus with a novel mosaic PTCH1 mutation.

The patched tumor suppressor gene (PTCH1) encodes a receptor, which is a key component of the hedgehog signalling pathway. Mutations in PTCH1 are implicated in the development of sporadic basal cell carcinomas (BCC), as well as those in Gorlin Syndrome. Rarely, BCCs may develop in a linear pattern along lines of Blaschko due to cutaneous mosaicism. In cases in which there are other features of Gorlin syndrome, genomic analysis has demonstrated lesional mutations in the Hedgehog signalling pathway. Causative mutations, however, have not been firmly demonstrated in the cases of linear and segmental BCCs in otherwise healthy individuals. Herein, we report a case of a 31 year-old Caucasian woman with linear development of multiple superficial BCCs in a Blaschkoid distribution without other characteristic findings of Gorlin syndrome. Genomic analysis of lesional skin by whole-exome sequencing identified a novel heterozygous mutation PTCH1: NM_000264.3, Exon 15, c.2336-2337insGGTAGGA, p.Asp779Glufs*13 in PTCH1, shared by two discrete samples within the lesion, while no mutations were found in the non-lesional skin or peripheral blood. Given the young age of our patient and linear distribution of BCCs on non-sun exposed skin, our findings suggest segmental mosaicism. The patient was treated with topical 5% imiquimod with histologically confirmed clearance of BCCs in 2 months.