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. Many 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 90% of affected individuals by age 30 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.

Darier-White disease (DAR), also known as keratosis follicularis, is an autosomal dominant skin disorder characterized by warty papules and plaques in seborrheic areas (central trunk, flexures, scalp, and forehead), palmoplantar pits, and distinctive nail abnormalities (Sakuntabhai et al., 1999). Onset is usually before the third decade, and penetrance is complete in adults, although expressivity is variable. Involvement may be severe, with widespread itchy malodorous crusted plaques, painful erosions, blistering, and mucosal lesions. Secondary infection is common. Sun, heat, and sweating exacerbate the symptoms. Darier disease never remits, but oral retinoids may reduce hyperkeratosis. Neuropsychiatric abnormalities, including mild mental retardation and epilepsy, have been described in association with Darier disease in a few families (Burge and Wilkinson, 1992); whether this is an association based on pleiotropism of the mutant gene or reflects coincidence is not clear. Histologic findings are (1) mild nonspecific perivascular infiltration in the dermis; (2) dermal villi protruding into the epidermis; (3) suprabasal detachment of the spinal layer leading to the formation of lacunae containing acantholytic cells; (4) in the more superficial epidermis, dyskeratotic round epidermal cells ('corps ronds'), the most distinctive feature; and (5) in the stratum corneum, 'grains' that resemble parakeratotic cells embedded in a hyperkeratotic horny layer. Electron microscopy reveals loss of desmosomal attachments, perinuclear aggregations of keratin filaments, and cytoplasmic vacuolization. Ultrastructural and immunologic studies suggest the disease results from an abnormality in the desmosome-keratin filament complex leading to a breakdown in cell adhesion.

Generalized basaloid follicular hamartoma syndrome is a rare, genetic skin disease characterized by multiple milium-like, comedone-like lesions and skin-colored to hyperpigmented, 1 to 2 mm-sized papules, associated with hypotrichosis and palmar/plantar pits. Lesions are usually first noticed on cheeks or neck and gradually increase in size and number to involve the scalp, face, ears, shoulders, chest, axillas, and upper arms. In severe cases, lower back, lower arms, and back of the legs can be involved. Mild hypohidrosis has also been reported.

Dowling-Degos disease-3 (DDD3) is an autosomal dominant disorder characterized by progressive spotted and reticulate pigmentation of the flexures (summary by Li et al., 2006). For a general phenotypic description and a discussion of genetic heterogeneity of Dowling-Degos disease, see DDD1 (179850).

Epidermodysplasia verruciformis-3 (EV3) is characterized by onset in childhood or early adulthood of persistent disseminated flat warts and pityriasis versicolor-like lesions of the skin that are induced by cutaneous human papillomaviruses (HPVs) of the beta genus. Some patients develop nonmelanoma skin cancer, particularly on areas of the body exposed to the sun. Patients are otherwise healthy and normally resistant to other microorganisms, including other viruses and skintropic pathogens, and even all other cutaneous and mucosal HPVs (de Jong et al., 2018). For a discussion of genetic heterogeneity of susceptibility to epidermodysplasia verruciformis, see EV1 (226400).

The basal cell nevus syndrome (BCNS), also known as Gorlin syndrome, is characterized by numerous basal cell cancers and epidermal cysts of the skin, calcified dural folds, keratocysts of the jaws, palmar and plantar pits, ovarian fibromas, medulloblastomas, lymphomesenteric cysts, fetal rhabdomyomas, and various stigmata of maldevelopment (e.g., rib and vertebral abnormalities, cleft lip or cleft palate, and cortical defects of bones) (summary by Koch et al., 2002). For a discussion of genetic heterogeneity of BCNS, see BCNS1 (109400).