Hypomelanosis of Ito: pigmentary mosaicism with immature melanosome in keratinocytes

Shining Light on Autophagy in Skin Pigmentation and Pigmentary Disorders

Autophagy is a vital process for cell survival and it preserves homeostasis by recycling or disassembling unnecessary or dysfunctional cellular constituents. Autophagy ameliorates skin integrity, regulating epidermal differentiation and constitutive pigmentation. It induces melanogenesis and contributes to skin color through melanosome turnover. Autophagy activity is involved in skin phenotypic plasticity and cell function maintenance and, if altered, it concurs to the onset and/or progression of hypopigmentary and hyperpigmentary disorders. Overexpression of autophagy exerts a protective role against the intrinsic metabolic stress occurring in vitiligo skin, while its dysfunction has been linked to the tuberous sclerosis complex hypopigmentation. Again, autophagy impairment reduces melanosome degradation by concurring to pigment accumulation characterizing senile lentigo and melasma. Here we provide an updated review that describes recent findings on the crucial role of autophagy in skin pigmentation, thus revealing the complex interplay among melanocyte biology, skin environment and autophagy. Hence, targeting this process may also represent a promising strategy for treating pigmentary disorders.

[Differential diagnostics of hypomelanoses]

Hypomelanoses of the skin encompass a wide spectrum of congenital and acquired alterations in melanin pigmentation. These diseases can be localized or universal. The pathobiology of cutaneous hypomelanoses is heterogeneous and includes defects in melanoblast migration from the neural crest to the epidermis, alterations in melanogenesis and melanin transfer to keratinocytes, and destruction of pigment cells by autoimmune and inflammatory processes. Importantly, some congenital forms of universal hypomelanoses are associated with involvement of internal organs (e.g., Hermansky-Pudlack or Chédiak-Higashi syndrome) and require interdisciplinary patient management. In recent years, significant progress has been made in our current understanding of the pathophysiology especially of vitiligo, thus, resulting in promising new treatment strategies. This disease being one of the most common forms of acquired hypomelanoses of the skin can now be treated in a guideline-oriented and evidence-based manner.

Cutaneous mosaicisms: concepts, patterns and classifications

A mosaic is an organism composed of two or more genetically distinct cell populations derived from a genetically homogeneous zygote. Cutaneous mosaicisms are the clinical expressions of these disorders. The main event which allows the existence of mosaicism is a genetic mutation, either structural or functional. Cutaneous mosaicisms usually manifest by specific patterns on the skin and the archetypic pattern is the system of Blaschko lines, but others include checkerboard, phylloid, large patches without midline separation and lateralization. Since 1901, when Blaschko lines were first described, the study of mosasicism has helped to elucidate the behavior of numerous genetic diseases, generating therapeutic perspectives for these pathologies, including the promising gene therapy.