Reticulate Acropigmentation Of Kitamura

A number sign (#) is used with this entry because of evidence that reticulate acropigmentation of Kitamura (RAK) is caused by heterozygous mutation in the ADAM10 gene (602192) on chromosome 15q21.

Description

Reticulate acropigmentation of Kitamura (RAK) is a rare pigmentary disorder that usually shows an autosomal dominant pattern of inheritance with high penetrance. Typical features include reticulate, slightly depressed, sharply demarcated brown macules without hypopigmentation, affecting the dorsa of the hands and feet in the first or second decade of life. The macules gradually darken and extend to the proximal regions of the extremities; progression of the eruptions stops in middle age. The increased pigmentation is found on the flexor aspects of the wrists, neck, patella, and olecranon. Other features include breaks in the epidermal ridges on the palms and fingers, palmoplantar pits, partial alopecia, and occasionally plantar keratoderma. Histopathologically, the brown macules show pigmentation in the tip of rete ridges with thinning of the epidermis, elongation and thinning of the rete ridges, and slight hyperkeratosis without parakeratosis. Only a few inflammatory cell infiltrates and no incontinentia pigmenti are seen in the dermis (summary by Kono 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 (see DDD1; 179850), 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.

Molecular Genetics

By whole-exome sequencing in a 4-generation Japanese family with autosomal dominant reticulate acropigmentation, Kono et al. (2013) identified a 5-bp insertion in the ADAM10 gene (602192.0001) that segregated with disease in the family and was not found in 102 Japanese controls. Sanger sequencing of ADAM10 in 5 more patients from 4 unrelated Japanese families identified 4 different mutations, including a splice site (602192.0002), a nonsense (Y143X; 602192.0003), and a missense (C524Y; 602192.0005) mutation as well as a 1-bp deletion (602192.0004). KRT5 (148040) mutations were excluded in all of the patients.