Two cases of KRT1 mutation-associated epidermolytic ichthyosis without typical epidermolytic hyperkeratosis in the neonatal skin lesions.

Epidermolytic ichthyosis (EI) is a rare genetic disorder of keratinization caused by mutations in either KRT1 or KRT10. Histopathologically, epidermolytic hyperkeratosis (EHK) is a hallmark of EI. Here, we report two EI cases in which KRT1 mutation was confirmed by molecular study, but without typical EHK present on skin biopsies performed within 1 week of age. Our cases demonstrate that EHK may not be evident in EI if skin biopsy is performed during the neonatal period.

Interleukin-18 as a severity marker and novel potential therapeutic target for epidermolytic ichthyosis.

BACKGROUND: Epidermolytic ichthyosis (EI) is a major form of nonsyndromic inherited ichthyosis, characterized by erythroderma, marked hyperkeratosis and scale, bulla and erosion at birth, associated with KRT1/KRT10 mutations. The cytokine and chemokine profiles in EI are poorly understood, and specific treatment options have not been established. AIM: To explore novel biomarkers and therapeutic targets in patients with EI. METHODS: We analysed cytokine levels in serum and skin samples from 10 patients with inherited ichthyosis, including seven patients with EI. Wild-type and mutant KRT1 constructs were established and transfected into HaCaT cells, an immortalized keratinocyte cell line, for in vitro immunoblotting and immunocytochemistry analyses. RESULTS: Multiplex cytokine/chemokine analysis revealed that 10 cytokines/chemokines [interleukin (IL)-1ß, IL-4, IL-17A, IL-16, IL-18, IL-1 receptor-α, macrophage colony-stimulating factor, interferon-α2, basic fibroblast growth factor and monocyte chemotactic protein-3] were significantly increased in patients with EI. Furthermore, IL-18 levels were significantly higher in patients with EI [n = 7; 2714.1 (1438.0) pg mL-1] than in healthy controls [n = 11; 218.4 (28.4) pg mL-1, P < 0.01]. Immunohistochemical analyses showed that IL-18 expression was elevated in skin samples from patients with EI. Serum IL-18 levels correlated with the severity of ichthyosis, as measured by the Ichthyosis Scoring System. Immunoblotting analysis revealed that mature IL-18 levels were increased in the supernatant of mutant KRT1 expressing HaCaT cells. Additionally, these cells showed NLRP3 aggregation in the cytoplasm and ASC clustered around mutant keratin aggregations. These findings suggest that mutant keratin might promote the activation of the NLRP3 inflammasome and its downstream caspase-1-mediated IL-18 release in keratinocytes from patients with EI. CONCLUSIONS: Our results suggest that serum IL-18 is a severity marker released from the skin of patients with EI. Blockade of IL-18 may be a useful novel therapeutic option for patients with EI.

A de novo variant in the keratin 1 gene (KRT1) in a Chinese shar-pei dog with severe congenital cornification disorder and non-epidermolytic ichthyosis.

A 3-months old Chinese shar-pei puppy with ichthyosis was investigated. The dog showed generalized scaling, alopecia and footpad lesions. Histopathological examinations demonstrated a non-epidermolytic hyperkeratosis. The parents of the affected puppy did not show any skin lesions. A trio whole genome sequencing analysis identified a heterozygous de novo 3 bp deletion in the KRT1 gene in the affected dog. This variant, NM_001003392.1:c.567_569del, is predicted to delete a single asparagine from the conserved coil 1A motif within the rod domain of KRT1, NP_001003392.1:p.(Asn190del). Immunohistochemistry demonstrated normal levels of KRT1 expression in the epidermis and follicular epithelia. This might indicate that the variant possibly interferes with keratin dimerization or another function of KRT1. Missense variants affecting the homologous asparagine residue of the human KRT1 cause epidermolytic hyperkeratosis. Histologically, the investigated Chinese shar-pei showed a non-epidermolytic ichthyosis. The finding of a de novo variant in an excellent functional candidate gene strongly suggests that KRT1:p.Asn190del caused the ichthyosis phenotype in the affected Chinese shar-pei. To the best of our knowledge, this is the first description of a KRT1-related non-epidermolytic ichthyosis in domestic animals.

Deep Phenotyping of Superficial Epidermolytic Ichthyosis due to a Recurrent Mutation in KRT2.

Superficial epidermolytic ichthyosis (SEI) is an autosomal dominant inherited ichthyosis. SEI is caused by mutations in KRT2 and frequently shows erythroderma and widespread blistering at birth. We report the clinical manifestations of two patients from a Japanese family with SEI caused by a hotspot mutation, p.Glu487Lys, in KRT2. In addition, we summarize previous reports on SEI patients with the identical mutation. One of the two patients had disease onset at the age of 7 months. The other patient's age of onset is unknown, but it was in childhood. Neither of the two patients showed erythroderma. To perform deep phenotyping, we studied the age of onset and the frequency of erythroderma in 34 reported SEI cases with the p.Glu487Lys mutation, including the present cases. Among the cases with sufficient clinical information, 44.4% of the cases that were due to p.Glu487Lys in KRT2 occurred at birth. Erythroderma was observed in 11.1% of the cases with p.Glu487Lys in KRT2.

Nonsense mutations in KRT1 caused recessive epidermolytic palmoplantar keratoderma with knuckle pads.

BACKGROUND: Epidermolytic palmoplantar keratoderma (EPPK) is characterized by diffuse hyperkeratosis affecting palms and soles with suprabasal epidermolysis or vacuolar degeneration histopathologically. The disorder is caused by heterozygous mutations in KRT9 or KRT1. Dominant-negative mutations in KRT1 could also result in epidermolytic ichthyosis with EPPK, a more severe entity affecting the entire body. OBJECTIVE: To investigate the genetic basis and pathogenesis of two unrelated patients with EPPK and knuckle pads, both of whom were born to consanguineous parents of Chinese origin. METHODS: Next-generation sequencing was applied to the two patients using genomic DNA extracted from peripheral blood. Quantitative reverse-transcriptase polymerase chain reaction (qRT-PCR), immunofluorescence (IF) staining and Western blot (WB) were employed to evaluate mRNA and protein expression level. Ultrastructural changes of skin lesion were analysed using transmission electron microscopy. RESULTS: Two novel homozygous mutations, c.457C>T (p.Gln153*) and c.33C>G (p.Tyr11*) in KRT1, were identified in patients 1 and 2 respectively. The nonsense mutations were predicted to result in nonsense-mediated mRNA decay and absence of keratin 1, which was confirmed in the skin lesions from patient 1. Upregulated keratin 2 was detected both in the affected and unaffected skin samples from patient 1, while the protein abundance and distribution pattern of keratin 10 remained unchanged. An aberrant and clumped staining pattern of keratin 9 was noted in the palmar skin of patient 1. CONCLUSIONS: Homozygous 'knockout' mutations in KRT1 resulted in EPPK with knuckle pads rather than epidermolytic ichthyosis. We speculated that sparing of non-acral skin might be due to compensatory effect of keratin 2 upregulation by forming heterodimer with keratin 10.

Transcriptomic Analysis of the Major Orphan Ichthyosis Subtypes Reveals Shared Immune and Barrier Signatures.

Preliminary work suggested upregulation of inflammatory pathways in patients with common forms of ichthyosis. However, a comprehensive characterization of skin from various ichthyosis subtypes is unavailable, precluding the development of targeted treatments. Thus, we sought to characterize the immune and barrier profiles of common and subtype-specific skin transcriptomes in a large group of patients with ichthyosis. We performed a global RNA-sequencing analysis in 54 patients with ichthyosis (7 with Netherton syndrome, 13 with epidermolytic ichthyosis, 16 with lamellar ichthyosis, and 18 with congenital ichthyosiform erythroderma) and 40 healthy controls. Differentially expressed genes were defined on the basis of fold changes > 2 and false discovery rate < 0.05 criteria. We found robust and significant T helper (Th) 22/Th17 skewing in all subtypes (e.g., IL-17A/C/F, S100A7/8/9/12; P < 0.001) with modest changes in Th2 pathway, primarily in Netherton syndrome, and Th1 skewing in congenital ichthyosiform erythroderma. Across all subtypes (less evident in epidermolytic ichthyosis), lipid metabolism and barrier junction markers were downregulated (e.g., FA2H, CDH10/11/12/2; P < 0.05), whereas epidermal cornification and proliferation measures were upregulated (e.g., SPRR1A/1B/2C/2G, EREG; P < 0.05). Our findings suggest that the common ichthyosis variants share aberrations in Th17/Th22 and barrier function, with minimal Th2 modulation. This may help to elucidate the pathogeneses of these subtypes and inform the development of subtype-specific treatments.

Annular Epidermolytic Ichthyosis Mimicking Greither Disease: A Case Report and Literature Review.

BACKGROUND Annular epidermolytic ichthyosis is a rare form of epidermolytic ichthyosis caused by specific pathogenic variants of KRT1 and KRT10. Classically, it manifests at birth with variable degrees of erythroderma and superficial erosions, which subsequently improve with time. Later, it is characterized by a cyclic history of annular hyperkeratotic erythematous plaques over the trunk and proximal extremities, with or without palmoplantar keratoderma. Greither syndrome, another autosomal dominant disorder of KRT1 mutation, is demonstrated by the diffuse, thick, scaly yellow PPK with transgrediens and erythematous border extending up to the Achilles' tendon, patchy hyperkeratotic plaques over the knees, shins, thighs, elbows, knuckles, and axillary folds. We describe a patient with clinical findings consistent with annular epidermolytic ichthyosis mimicking Greither disease with a likely associated pathogenic variant of KRT1. CASE REPORT A 3-year-old Saudi girl presented with a diffuse palmoplantar keratoderma (PPK) extending to the dorsal aspects of the hands and feet up to the Achilles' tendon, first noticed at the age of 3 months, with a history of recurrent coin-shaped erythematous crusted erosions over the trunk, which were spontaneously healed over time, and an associated history of hyperhidrosis. Patchy hyperkeratotic plaques were noticed upon further examination over the bilateral elbows, axillary folds, and oral commissures. CONCLUSIONS The phenotype of our patient is consistent with the clinical features described for AEI, making the new K1 variant a likely pathogenic variant. When K1 mutation is the causative variant of the disease expression, phenotypically, it can present with Greither-like PPK.

Scabies in a 14-year-old girl with superficial epidermolytic ichthyosis.

A 14-year-old girl who reported generalized scaling and hyperkeratosis since age 1 year presented with severe pruritus of several months' duration. Scabies mites were detected, and molecular genetic analysis subsequently revealed a rare pathogenic variant in the keratin 2 (KRT2) gene, confirming a diagnosis of superficial epidermolytic ichthyosis. Treatment with oral ivermectin led to complete remission of symptoms. Disorders of keratinization can mimic clinical signs of scabies, leading to a delay in diagnosis.

Epidermolytic ichthyosis in a child and systematized epidermolytic nevi in the mosaic parent associated with a KRT1 variant.

Epidermolytic ichthyosis and epidermolytic nevi share the same histopathological features of epidermolytic hyperkeratosis, characterized by distinctive vacuolar degeneration and hypergranulosis of the superficial epidermis. Both are caused by pathogenic variants in either of two keratin genes KRT1or KRT10, with epidermolytic ichthyosis presenting as a generalized phenotype and epidermolytic nevi presenting as a mosaic phenotype. We report a boy who presented as epidermolytic ichthyosis, with diffuse erythema, superficial erosions and flaccid blisters at birth progressing to generalized ichthyosis. He was found to have inherited a novel KRT1 variant from his mother who presented with extensive epidermolytic nevi or mosaic form of epidermolytic ichthyosis, with extensive, linear and Blaschkoid verrucous, hyperkeratotic plaques over the trunk and limbs. This case highlights the importance of recognising post-zygotic mosaicism which might be transmitted to a child, and the different presentations for germline and mosaic carriers.

Epidermolytic epidermal nevus caused by a somatic mutation in KRT2.

Superficial epidermolytic ichthyosis (formerly Ichthyosis bullosa of Siemens) is an uncommon condition caused by dominant mutations in KRT2 encoding keratin 2. Epidermolytic epidermal nevus due to somatic mutations in KRT2 is even rarer. Here, we report the third case of KRT2-associated epidermal nevus and review the literature.

TNF Is Partially Required for Cell-Death-Triggered Skin Inflammation upon Acute Loss of cFLIP.

cFLIP is required for epidermal integrity and skin inflammation silencing via protection from TNF-induced keratinocyte apoptosis. Here, we generated and analyzed cFLIP epidermal KO mice with additional TNF deficiency. Intriguingly, the ablation of TNF rescued the pathological phenotype of epidermal cFLIP KO from characteristic weight loss and increased mortality. Moreover, the lack of TNF in these animals strongly reduced and delayed the epidermal hyperkeratosis and the increased apoptosis in keratinocytes. Our data demonstrate that TNF signaling in cFLIP-deficient keratinocytes is the critical factor for the regulation of skin inflammation via modulated cytokine and chemokine expression and, thus, the attraction of immune cells. Our data suggest that autocrine TNF loop activation upon cFLIP deletion is dispensable for T cells, but is critical for neutrophil attraction. Our findings provide evidence for a negative regulatory role of cFLIP for TNF-dependent apoptosis and partially for epidermal inflammation. However, alternative signaling pathways may contribute to the development of the dramatic skin disease upon cFLIP deletion. Our data warrant future studies of the regulatory mechanism controlling the development of skin disease upon cFLIP deficiency and the role of cFLIP/TNF in a number of inflammatory skin diseases, including toxic epidermal necrolysis (TEN).

First Case of KRT2 Epidermolytic Nevus and Novel Clinical and Genetic Findings in 26 Italian Patients with Keratinopathic Ichthyoses.

Keratinopathic ichthyoses (KI) are a clinically heterogeneous group of keratinization disorders due to mutations in KRT1, KTR10, or KRT2 genes encoding keratins of suprabasal epidermis. Characteristic clinical features include superficial blisters and erosions in infancy and progressive development of hyperkeratosis. Histopathology shows epidermolytic hyperkeratosis. We describe the clinical, histopathological, and molecular findings of a series of 26 Italian patients from 19 unrelated families affected with (i) epidermolytic ichthyosis due to KRT1 or KRT10 mutations (7 and 9 cases, respectively); (ii) KTR10-mutated ichthyosis with confetti (2 cases); (iii) KRT2-mutated superficial epidermolytic ichthyosis (5 cases); and (iv) KRT10-mutated epidermolytic nevus (2 cases). Of note, molecular genetic testing in a third case of extensive epidermolytic nevus revealed a somatic missense mutation (p.Asn186Asp) in the KRT2 gene, detected in DNA from lesional skin at an allelic frequency of 25% and, at very low frequency (1.5%), also in blood. Finally, we report three novel dominant mutations, including a frameshift mutation altering the C-terminal V2 domain of keratin 1 in three familiar cases presenting a mild phenotype. Overall, our findings expand the phenotypic and molecular spectrum of KI and show for the first time that epidermolytic nevus can be due to somatic KRT2 mutation.

A de novo mutation of KRT1 in a baby girl causing epidermolytic ichthyosis with impressive epidermolytic palmoplantar keratoderma.

We report a 6-year-old girl showing epidermolytic ichthyosis/epidermolytic hyperkeratosis (EI/EH). Targeted Next Generation Sequencing revealed a de novo, previously unidentified KRT1 mutation. The findings of this study expands the clinical and  spectrum and genotype-phenotype correlation associated with EI/EH.