Bathing suit ichthyosis is caused by transglutaminase-1 deficiency: evidence for a temperature-sensitive phenotype

Cross-Sectional Study on Autosomal Recessive Congenital Ichthyoses: Association of Genotype with Disease Severity, Phenotypic, and Ultrastructural Features in 74 Italian Patients

BACKGROUND

Autosomal recessive congenital ichthyoses (ARCIs) are a clinically heterogeneous group of keratinization disorders characterized by generalized skin scaling due to mutations in at least 12 genes. The aim of our study was to assess disease severity, phenotypic, and ultrastructural features and to evaluate their association with genetic findings in ARCI patients.

METHODS

Clinical signs and symptoms, and disease severity were scored in a single-center series of patients with a genetic diagnosis of ARCI. Skin ultrastructural findings were reviewed.

RESULTS

Seventy-four consecutive patients (mean age 11.0 years, range 0.1-48.8) affected with lamellar ichthyosis (50/74, 67.5%), congenital ichthyosiform erythroderma (18/74, 24.3%), harlequin ichthyosis (two/74, 2.7%), and other minor ARCI subtypes (four/74, 5.4%) were enrolled. Mutated genes were as follows: TGM1 in 18/74 (24.3%) patients, ALOX12B in 18/74 (24.3%), CYP4F22 in 12/74 (16.2%), ABCA12 in nine/74 (12.2%), ALOXE3 in seven/74 (9.5%), NIPAL4 in seven/74 (9.5%), and CERS3, PNPLA1, and SDR9C7 in 1 patient each (1.4%). Twenty-five previously undescribed mutations in the different ARCI causative genes, as well as two microduplications in TGM1, and two microdeletions in CYP4F22 and NIPAL4 were identified. The mean ichthyosis severity score in TGM1- and ABCA12-mutated patients was significantly higher than in all other mutated genes, while the lowest score was observed in CYP4F22-mutated patients. Alopecia, ectropion, and eclabium were significantly associated with TGM1 and ABCA12 mutations, and large, thick, and brownish scales with TGM1 mutations. Among specific phenotypic features, psoriasis-like lesions as well as a trunk reticulate scale pattern and striated keratoderma were present in NIPAL4-mutated patients. Ultrastructural data available for 56 patients showed a 100% specificity of cholesterol clefts for TGM1-mutated cases and revealed abnormal lamellar bodies in SDR9C7 and CERS3 patients.

CONCLUSION

Our study expands the phenotypic and genetic characterization of ARCI by the description of statistically significant associations between disease severity, specific clinical signs, and different mutated genes. Finally, we highlighted the presence of psoriasis-like lesions in NIPAL4-ARCI patients as a novel phenotypic feature with diagnostic and possible therapeutic implications.

Comorbidity of bathing suit ichthyosis and limb-girdle muscular dystrophy type 2 A in a Tunisian patient revealed by Whole Exome Sequencing

Elevated rates of consanguinity and inbreeding are responsible for the high prevalence of recessively inherited diseases among inbred populations including Tunisia. In addition, the co-occurrence of two of these conditions, called also comorbidity, within the same individual or in members of the same family are often described in Tunisia which is challenging for diagnosis. The high throughput sequencing has improved the diagnosis of inherited diseases. We report here on a 32-year-old woman born to consanguineous parents. She presented with congenital ichthyosis and muscular dystrophy. She was primarily suspected as suffering from Chanarin-Dorfman syndrome (CDS) with unusual form. Screening of founder mutations allowed only the elucidation of the molecular etiology of Ichthyosis. As the result was inconclusive, Whole Exome Sequencing (WES) was conducted. WES data analysis led to the identification of a mutation in the CAPN3 gene underlying limb-girdle muscular dystrophy type 2A (LGMD2A). Sanger sequencing confirmed the familial segregation of mutations. This work presents the first case worldwide of individual comorbidity of bathing suit ichthyosis and LGMD2A. The co-occurrence of two diseases should be systematically considered when establishing a diagnosis especially in consanguineous populations. WES is a powerful tool for molecular diagnosis in particular for revealing comorbidities and rectifying the diagnosis.

Erythrokeratodermia Variabilis-like Phenotype in Patients Carrying ABCA12 Mutations

Erythrokeratodermia variabilis (EKV) is a rare genodermatosis characterized by well-demarcated erythematous patches and hyperkeratotic plaques. EKV is most often transmitted in an autosomal dominant manner. Until recently, only mutations in connexins such as GJB3 (connexin 31), GJB4 (connexin 30.3), and occasionally GJA1 (connexin 43) were known to cause EKV. In recent years, mutations in other genes have been described as rare causes of EKV, including the genes KDSR, KRT83, and TRPM4. Features of the EKV phenotype can also appear with other genodermatoses: for example, in Netherton syndrome, which hampers correct diagnosis. However, in autosomal recessive congenital ichthyosis (ARCI), an EKV phenotype has rarely been described. Here, we report on seven patients who clinically show a clear EKV phenotype, but in whom molecular genetic analysis revealed biallelic mutations in ABCA12, which is why the patients are classified in the ARCI group. Our study indicates that ARCI should be considered as a differential diagnosis in EKV.

Novel Compound Heterozygous Mutations of TGM1 Gene Identified in a Turkish Collodion Baby Diagnosed with Non-Bullous Congenital Ichthyosiform Erythroderma

Autosomal recessive congenital ichthyosis (ARCI) is a group of diseases presenting as collodion baby at birth. ARCI is categorized as Harlequin ichthyosis, lamellar ichthyosis, and non-bullous congenital ichthyosiform erythroderma (NBCIE), bathing suit icthyosis (BSI) and others. We describe the case of a male newborn with NBCIE whose whole exome sequencing revealed two variants of TGM1 gene (NM_000359.3) in a compound heterozygous state: c.790C>T (p.Arg264Trp) in exon 5 and c.2060G>A (p.Arg687His) in exon 13. In the literature, the Arg264Trp variant has been reported as homozygous or compound heterozygous with other variants in patients with BSI. In contrast, the Arg687His variant has been reported only as homozygous in patients with BSI. To the best of our knowledge, this is the first case whose two compound heterozygous variants, exhibiting the NBCIE phenotype, instead of the BSI.

Advanced Anterior Eye Segment Imaging for Ichthyosis

The purpose of this study was to describe ocular surface and anterior eye segment findings in various types of ichthyoses.

METHODS

This was a single-center prospective observational study. The study group consisted of five patients (P1-P5) aged 13-66 years. Multimodal imaging was performed, including slit-lamp examinations, swept-source optical coherence tomography (SS-OCT), and in vivo confocal microscopy (IVCM).

RESULTS

All patients were diagnosed with moderate-to-severe dry eye disease (DED). The corneas showed a significant pattern of irregularity, with a significant difference between the corneal thickness at the apex (CAT) and the corneal thinnest thickness (CTT), exceeding 375 µm. Three patients were diagnosed with ectasia patterns based on SS-OCT. All patients showed abnormalities in at least one Fourier index parameter for at least one eye at 3 or 6 mm in the keratometric, anterior, or posterior analyses. IVCM examinations revealed changes in all corneal layers.

CONCLUSIONS

By combining the results of multimodal imaging, we were able to detect preclinical abnormalities, distinguish characteristic changes common to ichthyosis, and reveal the depth and characteristics of corneal abnormalities. Therefore, patients with ichthyosis should be examined for DED and ectatic disorders early in clinical practice.

Acral lamellar ichthyosis with amino acid substitution in the C-terminus of keratin 2

BACKGROUND

Most cases of hereditary ichthyoses present with generalized scaling and skin dryness. However, in some cases skin involvement is restricted to particular body regions as in acral lamellar ichthyosis.

OBJECTIVES

We report on the genetic basis of acral ichthyosis in two families presenting with a similar phenotype.

METHODS

Genetic testing was performed by targeted next generation sequencing and whole-exome sequencing. For identity-by-descent analysis, the parents were genotyped and data analysis was performed with the Chromosome Analysis Suite Software. RT-PCR with RNA extracted from skin samples was used to analyse the effect of variants on splicing.

RESULTS

Genetic testing identified a few heterozygous variants, but only the variant in KRT2 c.1912 T > C, p.Phe638Leu segregated with the disease and remained the strongest candidate. Pairwise identity-by-descent analysis revealed no indication of family relationship. Phenylalanine 638 is the second last amino acid upstream of the termination codon in the tail of K2, and substitution to leucine is predicted as probably damaging. Assessment of the variant is difficult, in part due to the lack of crystal structures of this region.

CONCLUSIONS

Altogether, we show that a type of autosomal dominant acral ichthyosis is most probably caused by an amino acid substitution in the C-terminus of keratin 2.

Ichthyosis

The ichthyoses are a large, heterogeneous group of skin cornification disorders. They can be inherited or acquired, and result in defective keratinocyte differentiation and abnormal epidermal barrier formation. The resultant skin barrier dysfunction leads to increased transepidermal water loss and inflammation. Disordered cornification is clinically characterized by skin scaling with various degrees of thickening, desquamation (peeling) and erythema (redness). Regardless of the type of ichthyosis, many patients suffer from itching, recurrent infections, sweating impairment (hypohidrosis) with heat intolerance, and diverse ocular, hearing and nutritional complications that should be monitored periodically. The characteristic clinical features are considered to be a homeostatic attempt to repair the skin barrier, but heterogeneous clinical presentation and imperfect phenotype-genotype correlation hinder diagnosis. An accurate molecular diagnosis is, however, crucial for predicting prognosis and providing appropriate genetic counselling. Most ichthyoses severely affect patient quality of life and, in severe forms, may cause considerable disability and even death. So far, treatment provides only symptomatic relief. It is lifelong, expensive, time-consuming, and often provides disappointing results. A better understanding of the molecular mechanisms that underlie these conditions is essential for designing pathogenesis-driven and patient-tailored innovative therapeutic solutions.

Current Strategies for the Gene Therapy of Autosomal Recessive Congenital Ichthyosis and Other Types of Inherited Ichthyosis

Mutations in genes such as transglutaminase-1 (TGM1), which are responsible for the formation and normal functioning of a lipid barrier, lead to the development of autosomal recessive congenital ichthyosis (ARCI). ARCIs are characterized by varying degrees of hyperkeratosis and the presence of scales on the body surface since birth. The quality of life of patients is often significantly affected, and in order to alleviate the manifestations of the disease, symptomatic therapy with moisturizers, keratolytics, retinoids and other cosmetic substances is often used to improve the condition of the patients' skin. Graft transplantation is commonly used to correct defects of the eye. However, these approaches offer symptomatic treatment that does not restore the lost protein function or provide a long-term skin barrier. Gene and cell therapies are evolving as promising therapy for ARCIs that can correct the functional activity of altered proteins. However, these approaches are still at an early stage of development. This review discusses current studies of gene and cell therapy approaches for various types of ichthyosis and their further prospects for patient treatment.

Proteasome-mediated degradation of keratins 7, 8, 17 and 18 by mutant KLHL24 in a foetal keratinocyte model: Novel insight in congenital skin defects and fragility of epidermolysis bullosa simplex with cardiomyopathy

Epidermolysis bullosa simplex (EBS) with cardiomyopathy (EBS-KLHL24) is an EBS subtype caused by dominantly inherited, gain-of-function mutations in the gene encoding for the ubiquitin-ligase KLHL24, which addresses specific proteins to proteasomal degradation. EBS-KLHL24 patients are born with extensive denuded skin areas and skin fragility. Whilst skin fragility rapidly ameliorates, atrophy and scarring develop over time, accompanied by life-threatening cardiomyopathy. To date, pathogenetic mechanisms underlying such a unique disease phenotype are not fully characterized. The basal keratin 14 (K14) has been indicated as a KLHL24 substrate in keratinocytes. However, EBS-KLHL24 pathobiology cannot be determined by the mutation-enhanced disruption of K14 alone, as K14 is similarly expressed in foetal and postnatal epidermis and its protein levels are preserved both in vivo and in vitro disease models. In this study, we focused on foetal keratins as additional KLHL24 substrates. We showed that K7, K8, K17 and K18 protein levels are markedly reduced via proteasome degradation in normal foetal keratinocytes transduced with the mutant KLHL24 protein (ΔN28-KLHL24) as compared to control cells expressing the wild-type form. In addition, heat stress led to keratin network defects and decreased resilience in ΔN28-KLHL24 cells. The KLHL24-mediated degradation of foetal keratins could contribute to congenital skin defects in EBS-KLHL24. Furthermore, we observed that primary keratinocytes from EBS-KLHL24 patients undergo accelerated clonal conversion with reduced colony forming efficiency (CFE) and early replicative senescence. Finally, our findings pointed out a reduced CFE in ΔN28-KLHL24-transduced foetal keratinocytes as compared to controls, suggesting that mutant KLHL24 contributes to patients’ keratinocyte clonogenicity impairment.

Characterization of mutant type VII collagens underlying the inversa subtype of recessive dystrophic epidermolysis bullosa

BACKGROUND

Patients with recessive dystrophic epidermolysis bullosa (RDEB) lack functional type VII collagen (C7) leading to skin fragility, bullae, and erosive wounds. RDEB-Inversa (RDEB-I), a subset of RDEB, is characterized by lesions localized to body areas with higher skin temperatures such as flexures and skin folds.

OBJECTIVE

We aimed to determine if C7 derived from RDEB-I mutations had structural and functional aberrancies that were temperature sensitive and could be reversed by lowering the temperature.

METHODS

In this study, we generated 12 substitution mutations associated with RDEB-I via site-directed mutagenesis and purified recombinant C7 protein. These C7 mutants were evaluated for structural parameters (trimer formation and protease sensitivity) and the ability to promote keratinocyte migration at 37 °C (the temperature of skin folds) and 30 °C (the maximum skin temperature of arms and legs). Fibroblasts derived from RDEB-I patients were evaluated for C7 secretion and cellular migration at both temperatures.

RESULTS

C7s from RDEB-I mutations exhibited decreased thermal stability, increased sensitivity to protease digestion, diminished formation of collagen trimers, and reduced ability to promote keratinocyte migration compared with wild-type C7. In addition, fibroblasts derived from RDEB-I patients demonstrated intracellular accumulation of C7 and abnormal cell migration at 37 °C. All of these aberrancies were corrected by reducing the temperature to 30 °C. C7s generated from severe-RDEB mutations (non-Inversa) did not display temperature-dependent perturbations.

CONCLUSION

These data demonstrate that RDEB-I mutations generate C7 aberrancies that are temperature dependent. This may explain why RDEB-I patients develop clinical lesions in areas where their skin is considerably warmer.

Bathing suit ichthyosis: Two Burmese siblings and a review of the literature

Bathing suit ichthyosis (BSI) is a subtype of autosomal recessive congenital ichthyosis (ARCI) characterized by the development of large platelike scales mainly limited to the trunk. It is caused by temperature sensitive variants in transglutaminase 1, encoded by the gene TGM1. We describe a rare case of intrafamilial variation in phenotypic expressivity in two Burmese siblings with BSI that demonstrates the heterogeneity of the disorder within the same family and even in the same individual across time. We also present a concise review of the genotypic spectrum of BSI from 54 cases reported in the literature as evidence that both environmental and additional genetic factors can significantly alter the clinical phenotype.

Bathing Suit Variant of Autosomal Recessive Congenital Ichthyosis (ARCI) in Two Indian Patients

Bathing suit ichthyosis (BSI) is a rare variant of autosomal recessive congenital ichthyosis (ARCI) due to transglutaminase-1 gene (TGM1) mutations leading to a temperature sensitive phenotype. It is characterized by dark-grey or brownish scaling restricted to the "bathing suit" areas. We report two Indian girls with bathing suit ichthyosis and mutations in TGM1 (patient 1: homozygous for c.1147G>A; patient 2: compound heterozygous for c.832G>A, c.919C>G).

Autosomal recessive congenital ichthyosis: Genomic landscape and phenotypic spectrum in a cohort of 125 consanguineous families

Autosomal recessive congenital ichthyosis (ARCI), a phenotypically heterogeneous group of non-syndromic Mendelian disorders of keratinization, is caused by mutations in as many as 13 distinct genes. We examined a cohort of 125 consanguineous families with ARCI for underlying genetic mutations. The patients' DNA was analyzed with a gene-targeted next generation sequencing panel comprising 38 ichthyosis associated genes. The interpretations of results of genomic data were assisted by genome-wide homozygosity mapping and transcriptome sequencing. Sequence data analysis identified biallelic mutations in 106 families out of a total of 125 (85%), most of them (102, 96.2%) being homozygous, reflecting consanguinity in these families. Among the 85 distinct mutations in 10 different genes, 45 (53%) were previously unreported. Phenotype-genotype correlations allowed assignment of specific genes in the majority of the families to a specific subtype of ARCI, lamellar ichthyosis (LI) versus congenital ichthyosiform erythroderma (CIE). Interestingly, mutations in several genes could give rise to an overlapping phenotype consistent with either LI or CIE. Also, this is the third report for SDR9C7 and SULT2B1, and fourth report for CERS3 mutations. Direct comparison of our results with previously published regional cohorts highlights the global mutation landscape of ARCI, however, population specific differences were noted.

Transglutaminases in autoimmune and inherited skin diseases: The phenomena of epitope spreading and functional compensation

Transglutaminases (TGs) are structurally and functionally related enzymes that modify the post-translational structure and activity of proteins or peptides, and thus are able to turn on or switch off their function. Depending on location and activities, TGs are able to modify the signalling, the function and the fate of cells and extracellular connective tissues. Besides mouse models, human diseases enable us to appreciate the function of various TGs. In this study, skin diseases induced by genetic damages or autoimmune targeting of these enzymes will be discussed. TG1, TG3 and TG5 contribute to the cutaneous barrier and thus to the integrity and function of epidermis. TGM1 mutations related to autosomal recessive ichthyosis subtypes, TGM5 mutations to a mild epidermolysis bullosa phenotype and as novelty TGM3 mutation to uncombable hair syndrome will be discussed. Autoimmunity to TG2, TG3 and TG6 may develop in a few of those genetically determined individuals who lost tolerance to gluten, and manifest as coeliac disease, dermatitis herpetiformis or gluten-dependent neurological symptoms, respectively. These gluten responder diseases commonly occur in combination. In autoimmune diseases, the epitope spreading is remarkable, while in some inherited pathologies, a unique compensation of the lost enzyme function is noted.

Expanding the Genotypic Spectrum of Bathing Suit Ichthyosis

Importance

Bathing suit ichthyosis (BSI) is a rare congenital disorder of keratinization characterized by restriction of scale to sites of relatively higher temperature such as the trunk, with cooler areas remaining unaffected. Fewer than 40 cases have been reported in the literature. Bathing suit ichthyosis is caused by recessive, temperature-sensitive mutations in the transglutaminase-1 gene (TGM1). Clear genotype-phenotype correlations have been difficult to establish because several of the same TGM1 mutations have been reported in BSI and other forms of congenital ichthyosis. We identify novel and recurrent mutations in 16 participants with BSI.

Objective

To expand the genotypic spectrum of BSI, identifying novel TGM1 mutations in patients with BSI, and to use BSI genotypes to draw inferences about the temperature sensitivity of TGM1 mutations.

Design, Setting, and Participants

A total of 16 participants with BSI from 13 kindreds were identified from 6 academic medical centers. A detailed clinical history was obtained from each participant, including phenotypic presentation at birth and disease course. Each participant underwent targeted sequencing of TGM1.

Main Outcomes and Measures

Phenotypic and genotypic characteristics in these patients from birth onward.

Results

Of the 16 participants, 7 were male, and 9 were female (mean age, 12.6 years; range, 1-39 years). We found 1 novel TGM1 indel mutation (Ile469_Cys471delinsMetLeu) and 8 TGM1 missense mutations that to our knowledge have not been previously reported in BSI: 5 have been previously described in non-temperature-sensitive forms of congenital ichthyosis (Arg143Cys, Gly218Ser, Gly278Arg, Arg286Gln, and Ser358Arg), and 3 (Tyr374Cys, Phe495Leu, and Ser772Arg) are novel mutations. Three probands were homozygous for Arg264Trp, Arg286Gln, or Arg315Leu, indicating that these mutations are temperature sensitive. Seven of 10 probands with a compound heterozygous TGM1 genotype had a mutation at either arginine 307 or 315, providing evidence that mutations at these sites are temperature sensitive and highlighting the importance of these residues in the pathogenesis of BSI.

Conclusions and Relevance

Our findings expand the genotypic spectrum of BSI and the understanding of temperature sensitivity of TGM1 mutations. Increased awareness of temperature-sensitive TGM1 genotypes should aid in genetic counseling and provide insights into the pathophysiology of TGM1 ichthyoses, transglutaminase-1 enzymatic activity, and potential therapeutic approaches.

Summary of mutations underlying autosomal recessive congenital ichthyoses (ARCI) in Arabs with four novel mutations in ARCI-related genes from the United Arab Emirates

BACKGROUND

Clinical and molecular heterogeneity is a prominent characteristic of congenital ichthyoses, with the involvement of numerous causative loci. Mutations in these loci feature in autosomal recessive congenital ichthyoses (ARCIs) quite variably, with certain genes/mutations being more frequently uncovered in particular populations.

METHODS

In this study, we used whole exome sequencing as well as direct Sanger sequencing to uncover four novel mutations in ARCI-related genes, which were found in families from the United Arab Emirates. In silico tools such as CADD and SIFT Indel were used to predict the functional consequences of these mutations.

RESULTS

The here-presented mutations occurred in three genes (ALOX12B, TGM1, ABCA12), and these are a mixture of missense and indel variants with damaging functional consequences on their encoded proteins.

CONCLUSIONS

This study presents an overview of the mutations that were found in ARCI-related genes in Arabs and discusses molecular and clinical details pertaining to the above-mentioned Emirati cases and their novel mutations with special emphasis on the resulting protein changes.

Recent advances in understanding ichthyosis pathogenesis

The ichthyoses, also known as disorders of keratinization (DOK), encompass a heterogeneous group of skin diseases linked by the common finding of abnormal barrier function, which initiates a default compensatory pathway of hyperproliferation, resulting in the characteristic clinical manifestation of localized and/or generalized scaling. Additional cutaneous findings frequently seen in ichthyoses include generalized xerosis, erythroderma, palmoplantar keratoderma, hypohydrosis, and recurrent infections. In 2009, the Ichthyosis Consensus Conference established a classification consensus for DOK based on pathophysiology, clinical manifestations, and mode of inheritance. This nomenclature system divides DOK into two main groups: nonsyndromic forms, with clinical findings limited to the skin, and syndromic forms, with involvement of additional organ systems. Advances in next-generation sequencing technology have allowed for more rapid and cost-effective genetic analysis, leading to the identification of novel, rare mutations that cause DOK, many of which represent phenotypic expansion. This review focuses on new findings in syndromic and nonsyndromic ichthyoses, with emphasis on novel genetic discoveries that provide insight into disease pathogenesis.

Role of molecular testing in the multidisciplinary diagnostic approach of ichthyosis

Background

The term ichthyosis describes a generalized disorder of cornification characterized by scaling and/or hyperkeratosis of different skin regions. Mutations in a broad group of genes related to keratinocyte differentiation and epidermal barrier function have been demonstrated to play a causative role in disease development. Ichthyosis may be classified in syndromic or non-syndromic forms based on the occurrence or absence of extracutaneous signs. In this setting, the diagnosis of ichthyosis is an integrated multistep process requiring a multidisciplinary approach in order to formulate the appropriate diagnostic hypothesis and to address the genetic testing.

Methods

Due to the complex features of the different ichthyoses and the high number of genes involved we have investigated a group of 64 patients, affected by syndromic and non-syndromic diseases, using Next Generation Sequencing as a new tool for the molecular diagnosis.

Results

Using this innovative molecular approach we were able to find pathogenic mutations in 53 out of 64 patients resulting in 82.8 % total detection rate. An interesting result from the analysis of the data is the high rate of novel sequence variations found compared to known mutations and the relevant rate of homozygous mutations.

Conclusions

The possibility to analyze a large number of genes associated with various diseases allows to study cases with phenotypes not well-determined, giving the opportunity to make new genotype-phenotype correlation. In some cases there were discrepancies between clinical features and histology or electron microscopy and only molecular analysis allowed to definitively resolve the diagnostic dilemma. The genetic diagnosis of ichthyosis leads to a more accurate and effective genetic counseling, allowing correct evaluation of the risk of recurrence, particularly in families with consanguineous background.

Electronic supplementary material

The online version of this article (doi:10.1186/s13023-016-0384-4) contains supplementary material, which is available to authorized users.

Homozygous ALOXE3 Nonsense Variant Identified in a Patient with Non-Bullous Congenital Ichthyosiform Erythroderma Complicated by Superimposed Bullous Majocchi's Granuloma: The Consequences of Skin Barrier Dysfunction

Non-bullous congenital ichthyosiform erythroderma (NBCIE) is a hereditary disorder of keratinization caused by pathogenic variants in genes encoding enzymes important to lipid processing and terminal keratinocyte differentiation. Impaired function of these enzymes can cause pathologic epidermal scaling, significantly reduced skin barrier function. In this study, we have performed a focused, genetic analysis of a probrand affected by NBCIE and extended this to his consanguineous parents. Targeted capture and next-generation sequencing was performed on NBCIE associated genes in the proband and his unaffected consanguineous parents. We identified a homozygous nonsense variant c.814C>T (p.Arg272*) in ALOXE3 (NM_001165960.1) in the proband and discovered that his parents are both heterozygous carriers of the variant. The clinical manifestations of the proband’s skin were consistent with NBCIE, and detailed histopathological assessment revealed epidermal bulla formation and Majocchi’s granuloma. Infection with Trichophyton rubrum was confirmed by culture. The patient responded to oral terbinafine antifungal treatment. Decreased skin barrier function, such as that caused by hereditary disorders of keratinization, can increase the risk of severe cutaneous fungal infections and the formation of Majocchi’s granuloma and associated alopecia. Patients with NBCIE should be alerted to the possible predisposition for developing dermatophytoses and warrant close clinical follow-up.

Cathepsin D repairing role in photodamaged skin barrier

BACKGROUNDS/OBJECTIVES: Cathepsin D plays an important part in maintaining a normal skin barrier. Our previous study found that cathepsin D decreased in chronic photodamaged skin. This study investigated the cathepsin D content change in the stratum corneum (SC) and the repairing role of cathepsin D in chronic photodamaged skin barrier via the application of cathepsin D gel.

METHODS

Cathepsin D gel (0.001%) was applied to chronic photodamaged (sun-exposed forearm) human skin on identical sites (1 cm(2)/area) twice daily for 2 weeks. At 30 min and at 1, 3, 7, and 14 days, skin hydration and transepidermal water loss (TEWL) average values were detected via noninvasive skin detection equipment. Cathepsin D and transglutaminase (TGase)-1 in the skin sublayers were separated and detected via tape stripping, ELISA and Western blot.

RESULTS

After 2 weeks of cathepsin D gel application, the skin moisture value increased from 86.8 ± 1.2 to 95.2 ± 2.7 (p < 0.05), while TEWL decreased from 17.88 ± 1.87 to 11.58 ± 2.14 (p < 0.05). Cathepsin D protein was detected in the upper epidermis (12.6 ± 2.6 ng/cm(2)), mid-epidermis (8.4 ± 0.8 ng/cm(2)) and deep epidermis (16.2 ± 2.6 ng/cm(2)) in the cathepsin D gel group compared to the control group (2.2 ± 0.7, 3.0 ± 1.1 and 3.85 ± 1.4 ng/cm(2), respectively; p < 0.05). TGase-1 enzyme expression was upregulated 2.54 ± 0.19 times in the matrix gel-treated skin.

CONCLUSIONS

These data suggest that cathepsin D gel could increase the SC cathepsin D content and repair the epidermal barrier in chronic photodamaged skin. The mechanism might be related to increasing TGase-1 expression and activity.

A novel mutation in the transglutaminase-1 gene in an autosomal recessive congenital ichthyosis patient

Structure-function implication on a novel homozygous Trp250/Gly mutation of transglutaminase-1 (TGM1) observed in a patient of autosomal recessive congenital ichthyosis is invoked from a bioinformatics analysis. Structural consequences of this mutation are hypothesized in comparison to homologous enzyme human factor XIIIA accepted as valid in similar structural analysis and are projected as guidelines for future studies at an experimental level on TGM1 thus mutated.

Autosomal recessive congenital ichthyosis

The term autosomal recessive congenital ichthyosis (ARCI) refers to a group of rare disorders of keratinization classified as nonsyndromic forms of ichthyosis. This group was traditionally divided into lamellar ichthyosis (LI) and congenital ichthyosiform erythroderma (CIE) but today it also includes harlequin ichthyosis, self-healing collodion baby, acral self-healing collodion baby, and bathing suit ichthyosis. The combined prevalence of LI and CIE has been estimated at 1 case per 138 000 to 300 000 population. In some countries or regions, such as Norway and the coast of Galicia, the prevalence may be higher due to founder effects. ARCI is genetically highly heterogeneous and has been associated with 6 genes to date: TGM1, ALOXE3, ALOX12B, NIPAL4, CYP4F22, and ABCA12. In this article, we review the current knowledge on ARCI, with a focus on clinical, histological, ultrastructural, genetic, molecular, and treatment-related aspects.

Congenital lamellar ichthyosis in Tunisia is caused by a founder nonsense mutation in the TGM1 gene

Lamellar ichthyosis (LI, MIM# 242300) is a severe autosomal recessive genodermatosis present at birth in the form of collodion membrane covering the neonate. Mutations in the TGM1 gene encoding transglutaminase-1 are a major cause of LI. In this study molecular analysis of two LI Tunisian patients revealed a common nonsense c.788G>A mutation in TGM1 gene. The identification of a cluster of LI pedigrees carrying the c.788G>A mutation in a specific area raises the question of the origin of this mutation from a common ancestor. We carried out a haplotype-based analysis by way of genotyping 4 microsatellite markers and 8 SNPs flanking and within the TGM1 gene spanning a region of 6 Mb. Haplotype reconstruction from genotypes of all members of the affected pedigrees indicated that all carriers for the mutation c.788G>A harbored the same haplotype, indicating common ancestor. The finding of a founder effect in a rare disease is essential for the genetic diagnosis and the genetic counselling of affected LI pedigrees in Tunisia.

Revised nomenclature and classification of inherited ichthyoses: results of the First Ichthyosis Consensus Conference in Sorèze 2009

BACKGROUND

Inherited ichthyoses belong to a large, clinically and etiologically heterogeneous group of mendelian disorders of cornification, typically involving the entire integument. Over the recent years, much progress has been made defining their molecular causes. However, there is no internationally accepted classification and terminology.

OBJECTIVE

We sought to establish a consensus for the nomenclature and classification of inherited ichthyoses.

METHODS

The classification project started at the First World Conference on Ichthyosis in 2007. A large international network of expert clinicians, skin pathologists, and geneticists entertained an interactive dialogue over 2 years, eventually leading to the First Ichthyosis Consensus Conference held in Sorèze, France, on January 23 and 24, 2009, where subcommittees on different issues proposed terminology that was debated until consensus was reached.

RESULTS

It was agreed that currently the nosology should remain clinically based. "Syndromic" versus "nonsyndromic" forms provide a useful major subdivision. Several clinical terms and controversial disease names have been redefined: eg, the group caused by keratin mutations is referred to by the umbrella term, "keratinopathic ichthyosis"-under which are included epidermolytic ichthyosis, superficial epidermolytic ichthyosis, and ichthyosis Curth-Macklin. "Autosomal recessive congenital ichthyosis" is proposed as an umbrella term for the harlequin ichthyosis, lamellar ichthyosis, and the congenital ichthyosiform erythroderma group.

LIMITATIONS

As more becomes known about these diseases in the future, modifications will be needed.

CONCLUSION

We have achieved an international consensus for the classification of inherited ichthyosis that should be useful for all clinicians and can serve as reference point for future research.

Transglutaminase1 preferred substrate peptide K5 is an efficient tool in diagnosis of lamellar ichthyosis

Lamellar ichthyosis (LI) is a genetically heterogeneous, severe genodermatosis showing widespread hyperkeratosis of the skin. Transglutaminase 1 (TGase1) deficiency by TGase1 gene (TGM1) mutations is the most prevalent cause of LI. Screening of TGase1 deficiency in skin is essential to facilitate the molecular diagnosis of LI. However, cadaverine, the most widely used substrate for TGase activity assay, is not isozyme specific. Recently, a human TGase1-specific highly preferred substrate peptide K5 (pepK5) was generated. To evaluate its potential as a diagnostic tool for LI, we performed pepK5 labeling of TGase1 activity in normal human and LI skin. Ca(2+)-dependent labeling of FITC-pepK5 was clearly seen in the upper spinous and granular layers of normal human skin where it precisely overlapped with TGase1 immunostaining. Both specificity and sensitivity of FITC-pepK5 labeling for TGase1 activity were higher than those of FITC-cadaverine labeling. FITC-pepK5 labeling colocalized with involucrin and loricrin immunostaining at cornified cell envelope forming sites. FITC-pepK5 labeling was negative in LI patients carrying TGM1 truncation mutations and partially abolished in the other LI patients harboring missense mutations. The present results clearly indicate that pepK5 is a powerful tool for screening LI patient TGase1 deficiency when we make molecular diagnosis of LI.

Molekulare Charakterisierung der Ichthyosen

Ichthyosen umfassen eine ätiologisch heterogene Gruppe von genetisch bedingten Verhornungsstörungen, die die gesamte Haut betreffen und durch Hyperkeratose und/oder sichtbare Schuppung charakterisiert sind. Die Grundlagenforschung der vergangenen Jahre führte zur genetischen Aufklärung fast aller Ichthyoseformen und verbesserte die diagnostischen Möglichkeiten enorm. Hilfreiche Anlaufstellen für Ärzte und Patienten in Deutschland bieten das Netzwerk für Ichthyosen und verwandte Keratinisierungsstörungen (NIRK, www.netzwerk-ichthyose.de) und die Selbsthilfe Ichthyose e. V. (www.ichthyose.de) an. Im August 2009 wurde die weltweit erste Ichthyosekonsensusklassifikation verabschiedet. Deren Nosologie orientiert sich am klinischen Erscheinungsbild, berücksichtigt aber gleichzeitig die pathogenetischen Aspekte. Die grundlegende Einteilung basiert auf der Unterscheidung von syndromalen und nichtsyndromalen Formen. Bislang kontroverse Krankheitsnamen wurden neu definiert: Ichthyosen, die durch Keratinmutationen bedingt sind, werden unter dem neuen Überbegriff keratinopathische Ichthyose (KPI) geführt. Hierunter fallen die epidermolytische (Mutation in Keratin 1 oder 10) und die superfizielle epidermolytische Ichthyose (Keratin 2). Die Bezeichnung autosomal-rezessive kongenitale Ichthyose (ARCI) wird als ein Überbegriff für Harlekin-Ichthyose und für die Gruppe der lamellären Ichthyose und kongenitalen ichthyosiformen Erythrodermie verwendet. Die internationale Klassifikation soll als Referenz für zukünftige Untersuchungen der Erkrankungen dienen, z. B. bei Studien zur weiteren Genotyp-Phänotyp-Korrelation.

Ichthyosis: clinical manifestations and practical treatment options

Ichthyoses constitute a large group of cornification disorders that affect the entire integument. The skin is characterized by visible scaling and in many cases by inflammation, for example, in bullous/keratinopathic ichthyosis or Netherton syndrome. From the viewpoint of classification it is useful to distinguish non-syndromic from syndromic types of ichthyosis. Ichthyosis vulgaris and recessive X-linked ichthyosis are common disorders - often of delayed onset, in contrast to congenital ichthyoses, which belong to the group of rare diseases and present at birth with either the features of collodion membrane or congenital ichthyosiform erythroderma. The diagnostic steps are based on clinical data, analyses such as the steroid sulfatase activity test, skin biopsies, and genetic results. However, the dramatic increase in knowledge about the pathophysiology of these conditions has not led to a curative therapy so far. The therapeutic management is multidisciplinary and involves ichthyosis patient organizations in many countries. The mainstay of treatment remains with moisturizing creams containing, for example, urea, lactic acid and other humectants and keratolytics, regular bathing, and mechanical scale removal. Patients with lamellar ichthyosis or ichthyosiform erythroderma in particular profit from oral therapy with retinoids or retinoic acid metabolism-blocking agents.

Transglutaminase-1 gene mutations in autosomal recessive congenital ichthyosis: summary of mutations (including 23 novel) and modeling of TGase-1

Autosomal recessive congenital ichthyosis (ARCI) is a heterogeneous group of rare cornification diseases. Germline mutations in TGM1 are the most common cause of ARCI in the United States. TGM1 encodes for the TGase-1 enzyme that functions in the formation of the cornified cell envelope. Structurally defective or attenuated cornified cell envelop have been shown in epidermal scales and appendages of ARCI patients with TGM1 mutations. We review the clinical manifestations as well as the molecular genetics of ARCI. In addition, we characterized 115 TGM1 mutations reported in 234 patients from diverse racial and ethnic backgrounds (Caucasion Americans, Norwegians, Swedish, Finnish, German, Swiss, French, Italian, Dutch, Portuguese, Hispanics, Iranian, Tunisian, Moroccan, Egyptian, Afghani, Hungarian, African Americans, Korean, Japanese and South African). We report 23 novel mutations: 71 (62%) missense; 20 (17%) nonsense; 9 (8%) deletion; 8 (7%) splice-site, and 7 (6%) insertion. The c.877-2A>G was the most commonly reported TGM1 mutation accounting for 34% (147 of 435) of all TGM1 mutant alleles reported to date. It had been shown that this mutation is common among North American and Norwegian patients due to a founder effect. Thirty-one percent (36 of 115) of all mutations and 41% (29 of 71) of missense mutations occurred in arginine residues in TGase-1. Forty-nine percent (35 of 71) of missense mutations were within CpG dinucleotides, and 74% (26/35) of these mutations were C>T or G>A transitions. We constructed a model of human TGase-1 and showed that all mutated arginines that reside in the two beta-barrel domains and two (R142 and R143) in the beta-sandwich are located at domain interfaces. In conclusion, this study expands the TGM1 mutation spectrum and summarizes the current knowledge of TGM1 mutations. The high frequency of mutated arginine codons in TGM1 may be due to the deamination of 5' methylated CpG dinucleotides.

Novel transglutaminase-1 mutations and genotype-phenotype investigations of 104 patients with autosomal recessive congenital ichthyosis in the USA

BACKGROUND

Autosomal recessive congenital ichthyosis (ARCI) is a rare hereditary disorder of cornification. Mutations in the transglutaminase-1 (TGM1) gene, which encodes for the epidermal enzyme transglutaminase-1 (TGase-1), are one of the causes of ARCI.

METHODS

The TGM1 mutation spectrum was characterised and genotype-phenotype correlations investigated in 104 patients with ARCI ascertained through the National Registry for Ichthyosis and Related Disorders in the USA. Methods: Germline mutations in TGM1 were identified in 55% (57/104) of patients with ARCI. Arginine residues in TGase-1 were mutated in 39% (22/57) of patients overall and 54% (20/37) of those with missense mutations. In total, 55% (12/22) of missense mutations were within CpG dinucleotides and 92% (11/12) of these mutations were C-->T or G-->A transitions. The genotype-phenotype investigation found that ARCI with TGM1 mutations was significantly associated with presence of collodion membrane at birth (p = 0.006), ectropion (p = 0.001), plate-like scales (p = 0.005) and alopecia (p = 0.001). Patients who had at least one mutation predicted to truncate TGase-1 were more likely to have more severe hypohidrosis (p = 0.001) and overheating (p = 0.0007) at onset of symptoms than were those with exclusively TGM1 missense mutations. A logistic model was developed, which predicted that individuals with collodion membrane, alopecia and/or eye problems are about four times more likely to have TGM1 mutations than patients without these findings.

CONCLUSION

This is the largest investigation of patients with ARCI to date. It expands the TGM1 mutation spectrum and confirms that despite genetic and phenotypic heterogeneity in ARCI, TGM1 is the main causative gene for this disorder. The high frequency of mutated arginine codons in TGM1 may be due to the deamination of CpG dinucleotides.

Palifermin-induced flexural hyperpigmentation: a clinical and histological study of five cases

Palifermin is a human keratinocyte growth factor that is efficacious in reducing duration and severity of oral mucositis during autologous haematopoietic stem-cell transplantation for haematological cancer as well as chemotherapy for colorectal cancers. We report the clinical and histological characteristics of a series of five patients who developed flexural hyperpigmentation after treatment with palifermin. All patients showed ill-defined symmetrical hyperpigmented papillomatous plaques with slight erythema in the skin folds, especially affecting axillary and inguinal areas. The most striking histological finding was the thickened granular layer in all patients. We demonstrate that filaggrin, an essential component in the terminal differentiation of the epidermis, was upregulated in these cases. Palifermin-induced flexural hyperpigmentation is a newly defined clinical and histological entity. The possible aetiology is discussed.