Background: Linear unilateral basal cell nevus represents a linear collection of macules and papules histologically similar to basal cell carcinoma but with benign clinical behavior. We describe a patient who initially presented at the age of 6 months with a unilateral linear basal cell nevus on the right flank. The differential diagnosis included the nevoid basal cell carcinoma syndrome. Constitutional PTCH mutations are causative of the nevoid basal cell carcinoma syndrome, and somatic PTCH mutations are found in the vast majority of basal cell carcinomas. Somatic SMO mutations have also been found in some basal cell carcinomas.
Methods: Histologic examination of the lesions is performed. Short tandem-repeat molecular analysis at the PTCH locus and sequencing of PTCH and SMO genes is performed.
Results: Histologic examination revealed features initially indistinguishable from basal cell carcinoma. Short tandem-repeat DNA analysis did not reveal loss of heterozygosity at the PTCH locus. DNA sequencing of both the PTCH and the SMO genes from the patient's lesions revealed neither inactivating mutations of PTCH nor activating mutations of SMO.
Conclusion: Molecular examination indicates that the PTCH and SMO genes are not involved in the pathogenesis of the patients' congenital linear unilateral basal cell nevus. Furthermore, we discuss the relationship between linear basal cell nevus and basaloid follicular hamartoma.