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.

Polycystic dysgenetic disease of the parotid gland (PDDP) is a rare benign condition of the parotid gland. The disorder presents often in childhood or young adulthood, but may occur later in life. It occurs most commonly in females. Features include fluctuating and nontender swelling of the parotid gland bilaterally, without defects in salivary function. Histology shows replacement of the lobular portion of the parotid gland by multiple epithelial-lined cysts arising from the intercalated ducts. The cysts often contain altered salivary secretions, including spheroliths or microliths; eosinophilic congophilic deposits have also been described. Chronic inflammation is not present. The condition is thought to result from a developmental defect of the intercalated duct system. Surgery may be indicated for diagnosis or for cosmetic reasons (summary by Smyth et al., 1993; Layfield and Gopez, 2002; Eley et al., 2011).