Nevoid Basal Cell Carcinoma Syndrome

CLINICAL CHARACTERISTICS: Nevoid basal cell carcinoma syndrome (NBCCS) is characterized by the development of multiple jaw keratocysts, frequently beginning in the second decade of life, and/or basal cell carcinomas (BCCs) usually from the third decade onward. Approximately 60% of individuals have a recognizable appearance with macrocephaly, frontal bossing, coarse facial features, and facial milia. Most individuals have skeletal anomalies (e.g., bifid ribs, wedge-shaped vertebrae). Ectopic calcification, particularly in the falx, is present in more than 90% of affected individuals by age 20 years. Cardiac and ovarian fibromas occur in approximately 2% and 20% of individuals respectively. Approximately 5% of all children with NBCCS develop medulloblastoma (primitive neuroectodermal tumor), generally the desmoplastic subtype. The risk of developing medulloblastoma is substantially higher in individuals with an SUFU pathogenic variant (33%) than in those with a PTCH1 pathogenic variant (<2%). Peak incidence is at age one to two years. Life expectancy in NBCCS is not significantly different from average. DIAGNOSIS/TESTING: The diagnosis of NBCCS is established in a proband who fulfills existing diagnostic clinical criteria. Identification of a heterozygous germline pathogenic variant in PTCH1 or SUFU on molecular genetic testing establishes the diagnosis if clinical features are inconclusive. MANAGEMENT: Treatment of manifestations: Best provided by specialists experienced with the condition; keratocysts usually require surgical excision; early treatment of BCCs to ensure complete eradication of aggressive BCCs and to preserve normal tissue to prevent disfigurement; sonic hedgehog inhibitors such as vismodegib to treat severe BCCs; preservation of ovarian tissue whenever ovarian fibromas require surgical treatment. However, the cost of treatment has meant that the National Institute for Health and Care Excellence in the UK has judged the treatment not cost effective. Prevention of primary manifestations: Avoidance of direct sun exposure through the use of complete sunblock and covering of exposed skin with long sleeves, high collars, and hats. Surveillance: Monitoring of head circumference throughout childhood; developmental assessment and physical examination every six months in the first years of life because of increased risk for medulloblastoma; in those older than age eight years, orthopantogram every 12-18 months to identify jaw keratocysts; skin examination at least annually. Agents/circumstances to avoid: Radiotherapy if there are alternative treatments, especially in childhood; diagnostic x-rays should be used sparingly; direct sun exposure should be limited; excessive sun exposure increases the likelihood of developing BCCs. Evaluation of relatives at risk: Because of the need for surveillance for complications of NBCCS (medulloblastoma in children; jaw cysts and BCCs in adults) and the need to avoid sun exposure, clarification of the genetic status of at-risk relatives, including children, is appropriate. GENETIC COUNSELING: NBCCS is inherited in an autosomal dominant manner. Approximately 70%-80% of individuals with NBCCS have an affected parent and about 20%-30% have NBCCS as the result of a de novo pathogenic variant. The offspring of an affected individual are at a 50% risk of inheriting NBCCS. Prenatal testing for pregnancies at risk is possible if the PTCH1 or SUFU pathogenic variant has been identified in an affected family member.