Malignant atrophic papulosis (MAP) is a rare, chronic, thrombo-obliterative vasculopathy characterized by papular skin lesions with central porcelain-white atrophy and a surrounding teleangiectatic rim. Systemic lesions may affect the gastrointestinal tract and the central nervous system (CNS) and are potentially lethal.

Dermatopathia pigmentosa reticularis (DPR) is a rare heritable disorder consisting of a triad of cutaneous findings including reticulate hyperpigmentation, noncicatricial alopecia, and onychodystrophy. Variable features include adermatoglyphia, hypohidrosis or hyperhidrosis, and palmoplantar hyperkeratosis (Heimer et al., 1992).

Ring dermoid of cornea (RDC) is an autosomal dominant condition characterized by bilateral annular limbal dermoids with corneal and conjunctival extension (summary by Xia et al., 2004).

White sponge nevus is a rare autosomal dominant disorder of noncornifying squamous epithelial differentiation that presents clinically as white, soft, thick plaques of the oral mucosa. Less frequently, the mucous membranes of the nose, esophagus, genitalia, and rectum are involved. Histopathologic features, including epithelial thickening, parakeratosis, extensive vacuolization of the suprabasal keratinocytes, and compact aggregates of keratin intermediate filaments in the upper spinus layers resemble those found in epidermal disorders shown to be associated with keratin defects (summary by Richard et al., 1995). Genetic Heterogeneity of White Sponge Nevus White sponge nevus-2 (WSN2; 615785) is caused by mutation in the KRT13 gene (148065) on chromosome 17q21.

Pterygium of the conjunctiva refers to a wing-shaped thickening in the bulbar conjunctiva. The process begins near one corner of the eye, most commonly the inner canthus. The progressive head is typically fleshy and can infiltrate the cornea and block vision. Surgical excision is curative, although recurrence may occur after surgical removal (summary by Hecht and Shoptaugh, 1990). Reviews Saw and Tan (1999) reviewed the prevalence, demography, and risk factors for pterygium, noting that surveys had revealed an increased prevalence in countries between 37 degrees north and south of the equator, suggesting that ultraviolet light might be a risk factor in the development of pterygia. Other studies showed that pterygium was a proliferative rather than a degenerative disease. The authors concluded that it was unlikely that there was a sole risk factor for pterygium, and that other possible contributing factors included age, hereditary factors, and dry eyes.