Ultraviolet (UV) radiation is among the most prevalent environmental factors that influence human health and disease. Even 1 h of UV irradiation extensively damages the genome. To cope with resulting deleterious DNA lesions, cells activate a multitude of DNA damage response pathways, including DNA repair. Strikingly, UV‐induced DNA damage formation and repair are affected by chromatin state. When cells enter S phase with these lesions, a distinct mutation signature is created via error‐prone translesion synthesis. Chronic UV exposure leads to high mutation burden in skin and consequently the development of skin cancer, the most common cancer in the United States. Intriguingly, UV‐induced oxidative stress has opposing effects on carcinogenesis. Elucidating the molecular mechanisms of UV‐induced DNA damage responses will be useful for preventing and treating skin cancer with greater precision. Excitingly, recent studies have uncovered substantial depth of novel findings regarding the molecular and cellular consequences of UV irradiation. In this review, we will discuss updated mechanisms of UV‐induced DNA damage responses including the ATR pathway, which maintains genome integrity following UV irradiation. We will also present current strategies for preventing and treating nonmelanoma skin cancer, including ATR pathway inhibition for prevention and photodynamic therapy for treatment.

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Impetigo herpetiformis (IH) is a rare variant of generalized pustular psoriasis (GPP), which develops during pregnancy. GPP is associated with mutations of IL36RN, but it is still unclear whether the same is true of IH. A 20-year-old Japanese woman developed erythema and pustules on her trunk during the 27th week of her first pregnancy.

The palmoplantar keratodermas (PPKs) are a large group of genodermatoses comprising nearly 60 genetically distinct diseases. They are characterized by hyperkeratosis on the palms and soles with or without extrapalmoplantar hyperkeratotic lesions. Focal PPK is one of the hallmarks of pachyonychia congenita, a rare autosomal dominant disorder resulting from mutations in the keratin genes KRT6A, KRT6B, KRT16 or KRT17. Recently, in-frame deletion mutations of KRT6C have been identified in three families with focal PPK with slight or no nail changes. We report here a novel KRT6C mutation identified in a Japanese family with PPK with phenotypic heterogeneity, presenting with not only focal but also diffuse hyperkeratosis. The proband had diffuse hyperkeratosis on the soles and small focal hyperkeratoses on the palms, while the two other affected individuals showed focal hyperkeratoses on the soles. All three patients were heterozygotes for c.1414G>A in KRT6C, predicted to result in p.Glu472Lys. These findings strongly suggest that screening of patients with nonepidermolytic diffuse PPK, in whom the pathogenic mutations are yet to be determined, might identify mutations in KRT6C.

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