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Background: Hereditary palmoplantar keratodermas (hPPKs) comprise a heterogeneous group of skin disorders characterized by persistent palmoplantar hyperkeratosis. Loss‐of‐function variants in a serine peptidase inhibitor, SERPINA12, have recently been implicated in autosomal recessive diffuse hPPK. The disorder appears to share similarities with another hPPK associated with protease overactivity, namely Nagashima‐type PPK (NPPK) caused by biallelic variants in SERPINB7. Objectives: The aim of this study was to enhance the understanding of the clinical and genetic characteristics of serine protease‐related hPPKs caused by variants in SERPINA12 and SERPINB7. Methods: Whole‐exome sequencing (WES) was performed for hPPK patients. Haplotype analysis was completed for the patients with identified recessive SERPINA12 variants and their available family members. In addition, the current literature of SERPINA12‐ and SERPINB7‐related hPPKs was summarized. Results: The phenotype of SERPINA12‐related hPPK was confirmed by reporting three new SERPINA12 patients, the first of European origin. A novel SERPINA12 c.1100G>A p.(Gly367Glu) missense variant was identified confirming that the variant spectrum of SERPINA12 include both truncating and missense variants. The previously reported SERPINA12 c.631C>T p.(Arg211*) was indicated enriched in the Finnish population due to a plausible founder effect. In addition, SERPINA12 hPPK patients were shown to share a similar phenotype to patients with recessive variants in SERPINB7. The shared phenotype included diffuse transgradient PPK since birth or early childhood and frequent palmoplantar hyperhidrosis, aquagenic whitening and additional hyperkeratotic lesions in non‐palmoplantar areas. SERPINA12 and SERPINB7 hPPK patients cannot be distinguished without genetic analysis. Conclusions: Recessive variants in SERPINA12 and SERPINB7 leading to protease overactivity and hPPK produce a similar phenotype, indistinguishable without genetic analysis. SERPINA12 variants should be assessed also in non‐Asian patients with diffuse transgradient PPK. Understanding the role of serine protease inhibitors will provide insights into the complex proteolytic network in epidermal homeostasis. [ABSTRACT FROM AUTHOR]

Background: Hereditary palmoplantar keratodermas (PPK) represent a heterogeneous group of rare skin disorders with epidermal hyperkeratosis of the palms and soles, with occasional additional manifestations in other tissues. Mutations in at least 69 genes have been implicated in PPK, but further novel candidate genes and mutations are still to be found. Objectives: To identify mutations underlying PPK in a cohort of 64 patients. Methods: DNA of 48 patients was analysed on a custom‐designed in‐house panel for 35 PPK genes, and 16 patients were investigated by a diagnostic genetic laboratory either by whole‐exome sequencing, gene panels or targeted single‐gene sequencing. Results: Of the 64 PPK patients, 32 had diffuse (50%), 19 focal (30%) and 13 punctate (20%) PPK. None had striate PPK. Pathogenic mutations in altogether five genes were identified in 31 of 64 (48%) patients, the majority (22/31) with diffuse PPK. Of them, 11 had a mutation in AQP5, five in SERPINB7, four in KRT9 and two in SLURP1. AAGAB mutations were found in nine punctate PPK patients. New mutations were identified in KRT9 and AAGAB. No pathogenic mutations were detected in focal PPK. Variants of uncertain significance (VUS) in PPK‐associated and other genes were observed in 21 patients that might explain their PPK. No suggestive pathogenic variants were found for 12 patients. Conclusions: Diffuse PPK was the most common (50%) and striate PPK was not observed. We identified pathogenic mutations in 48% of our PPK patients, mainly in five genes: AQP5, AAGAB, KRT9, SERPINB7 and SLURP1. [ABSTRACT FROM AUTHOR]

The expression of type XV collagen was studied in cultured human dermal fibroblasts exposed to transforming growth factor- β (TGF- β), tumor necrosis factor- ??? (TNF- ???) or interleukin-1 β (IL-1 β), cytokines which have been shown previously to alter the expression of several extracellular matrix genes. TGF- β enhanced the expression of the type XV collagen gene (COL15A1) in a time-dependent manner, up to 4.3-fold after 24 h of incubation, whereas TNF- ??? and IL-1&beta reduced the mRNA steady-state levels by 32 and 80%, respectively. When TGF- β and TNF- ??? were added together to the cultures, the stimulatory effect of TGF- β on type XV collagen gene expression was abrogated, indicating antagonistic modulation by these 2 cytokines. These data suggest that the cytokines tested in this study may contribute to the regulation of type XV collagen synthesis in a variety of tissues which have recently been shown to express this particular collagen gene. [ABSTRACT FROM AUTHOR]