The Curth-Macklin type of ichthyosis hystrix (IHCM) is clinically characterized by severe fissuring and mutilating palmoplantar keratoderma. Affected individuals also exhibit extensive dark spiky or verrucous hyperkeratotic plaques over the large joints and trunk, which in some patients may cover almost the entire body. Structural and ultrastructural hallmarks include compact orthokeratotic hyperkeratosis, hypergranulosis with perinuclear edema, binucleated cells, and formation of perinuclear filamentous shells composed of feathery entangled keratin intermediate filaments (summary by Richardson et al., 2006 and Fonseca et al., 2013). The Lambert type of ichthyosis hystrix (IHL; 146600), in which palms and soles are spared, is caused by mutation in the KRT10 (148080) gene.

Dowling-Degos disease (DDD) is an autosomal dominant genodermatosis characterized by reticular pigmentation, usually in a flexural distribution. However, generalized DDD can also occur, with numerous hypopigmented or erythematous macules and papules on the neck, chest, and abdomen. The histopathology of DDD shows characteristic thin branch-like patterns of epidermal downgrowth (summary by Li et al., 2013). Review of Reticulate Pigment Disorders Muller et al. (2012) reviewed the spectrum of reticulate pigment disorders of the skin, tabulating all reported cases of patients with Dowling-Degos disease, reticulate acropigmentation of Kitamura (RAK), reticulate acropigmentation of Dohi (DSH, RAD; 127400), Galli-Galli disease (GGD), and Haber syndrome (HS). Of 82 cases, 26 (31.7%) were clinically diagnosed as DDD, 13 (15.9%) as RAD, 11 (13.4%) as GGD, 8 (9.8%) as RAK, and 8 (9.8%) as HS; in addition, 16 (19.5%) of the cases showed overlap between DDD and RAK. Muller et al. (2012) also published photographs of an affected individual exhibiting an overlap of clinical features of DDD, GGD, RAD, and RAK. The authors noted that in reticulate disorders of the skin, the main disease entity is DDD, with a subset of cases exhibiting acantholysis (GGD), facial erythema (HS), or an acral distribution (RAD; RAK). Muller et al. (2012) concluded that all reticulate pigment diseases of the skin are varying manifestations of a single entity. For a discussion of genetic heterogeneity of reticulate pigment disorders, see 179850.

Cole disease (COLED) is a rare autosomal dominant disorder characterized by congenital or early-onset punctate keratoderma associated with irregularly shaped hypopigmented macules, which are typically found over the arms and legs but not the trunk or acral regions. Skin biopsies of palmoplantar lesions show nonspecific changes including hyperorthokeratosis, hypergranulosis, and acanthosis. Hypopigmented areas of skin, however, reveal a reduction in melanin content in keratinocytes but not in melanocytes, as well as hyperkeratosis and a normal number of melanocytes. Ultrastructurally, melanocytes show a disproportionately large number of melanosomes in the cytoplasm and dendrites, whereas keratinocytes show a paucity of these organelles, suggestive of impaired melanosome transfer (summary by Eytan et al., 2013). Some patients also exhibit calcinosis cutis or early-onset calcific tendinopathy (Eytan et al., 2013).