Variants in the L12 linker domain of KRT10 are causal to atypical epidermolytic ichthyosis.

Epidermolytic ichthyosis (EI) is a type of congenital ichthyosis, characterized by erythema and blistering at birth followed by hyperkeratosis. EI is caused by pathogenic variants in the genes KRT1 and KRT10, encoding the proteins keratin 1 (KRT1) and keratin 10 (KRT10), respectively, and is primarily transmitted by autosomal-dominant inheritance, although recessive inheritance caused by nonsense variants in KRT10 is also described. The keratins form a network of intermediate filaments and are a structural component of the cytoskeleton, giving strength and resilience to the skin. We present three cases of mild EI caused by pathogenic KRT10 variations in the L12 linker domain. To our knowledge, this is the first time L12 linker domain pathogenic variants are identified in KRT10 for EI. The aim of this study was to identify gene variants for patients with EI in KRT1 or KRT10. To establish the pathogenicity of the found variations in KRT10, we evaluated all patients and available family members clinically. Genetic analyses were performed using Sanger sequencing. Vectors containing wild-type or mutated forms of KRT10 were transfected into HaCaT cells and analyzed by high-resolution confocal microscopy. Genetic analysis of KRT10 identified a heterozygous de novo variant c.910G>A p.(Val304Met) in family 1, a familial heterozygous variant c.911T>C p.(Val304Ala) in family 2, and a familial heterozygous variant c.917T>C p.(Met306Thr) in family 3. All identified missense variants were located in the L12 linker domain of KRT10. In vitro study of aggregate formation of the missense variants in KRT10 only showed a very mild and not quantifiable aggregate formation in the KRT10 network, compared with the wild-type sequence. We report three different novel missense variants in the L12 linker domain of KRT10 in patients with an atypical, milder form of EI resembling peeling skin syndrome.