Reticulate pigmentary disorders are autosomal dominant pigmentary disorders caused by abnormalities in the keratin 5 and keratin 14 genes. Here, we report three cases of reticulate hyperpigmentation disorders with clinical overlaps of the reticulate acropigmentation of Kitamura, Dowling-Degos disease (DDD), and dyschromatosis symmetrica hereditaria (DSH), all three having limited treatment options.

Reticulate pigmentary disorders (RPDs) are a group of inherited and acquired skin conditions characterized by hyperpigmented and/or hypopigmented macules. Inherited RPDs include dyschromatosis symmetrica hereditaria (DSH), dyschromatosis universalis hereditaria (DUH), reticulate acropigmentation of Kitamura (RAK), Dowling-Degos disease (DDD), dyskeratosis congenita (DKC), Naegeli-Franceschetti-Jadassohn syndrome (NFJS), dermatopathia pigmentosa reticularis (DPR), and X-linked reticulate pigmentary disorder. Although reticulate pattern of pigmentation is a common characteristic of this spectrum of disorders, the distribution of pigmentation varies among these disorders, and there may be clinical manifestations beyond pigmentation. DSH, DUH, and RAK are mostly reported in East Asian ethnicities. DDD is more common in Caucasians, although it is also reported in Asian countries. Other RPDs show no racial predilection. This article reviews the clinical, histological, and genetic variations of inherited RPDs.

Dyschromatosis symmetrica hereditaria (DSH) and reticulate acropigmentation of Kitamura (RAK) are rare, inherited pigmentary diseases. DSH shows a mixture of pigmented and depigmented macules on the extremities. RAK shows reticulated, slightly depressed pigmented macules on the extremities. The causative gene of DSH was clarified as ADAR1 by positional cloning including linkage analysis and haplotype analysis in 2003. Ten years later, the causative gene of RAK was identified as ADAM10 by whole-exome sequencing, in 2013. ADAR1 is an RNA-editing enzyme which catalyzes the deamination of adenosine to inosine (A-to-I) in double-stranded RNA substrates during post-transcription processing. Inosine acts as guanine during translation, resulting in codon alterations or alternative splice sites that lead to functional changes in proteins when they occur in coding regions. In 2012, it was clarified that ADAR1 mutations cause Aicardi-Goutières syndrome 6, which is a severe genetic inflammatory disease that affects the brain and the skin. A zinc metalloprotease, a disintegrin and metalloprotease domain-containing protein 10 (ADAM10), is involved in the ectodomain shedding of various membrane proteins and shows various functions in vivo. ADAM10 is known to be involved in the ectodomain shedding of Notch proteins as substrates in the skin. We speculate that the pathogenesis of RAK and Dowling-Degos disease (DDD, a pigmentary disease similar to RAK) is associated with the Notch signaling pathway. In addition, ADAM10 mutations proved to be associated with late-onset Alzheimer disease. This review comprehensively discusses the updated pathophysiology of those genetic pigmentary disorders.

Reticulate acropigmentation of Kitamura (RAK) is a rare, autosomal dominant disorder first described in Japan characterised by a reticulate pattern of slightly atrophic, angulated, hyperpigmented macules affecting the acral areas of the body. We hereby report a case of RAK in a young Indian male with adermatoglyphia that has not been previously reported in the literature.