Inherited ichthyoses/generalized Mendelian disorders of cornification

Revisiting X-linked congenital ichthyosis

X-linked recessive ichthyosis (XLI) is a hereditary skin disease characterized by generalized dryness and scaling of the skin, with frequent extracutaneous manifestations. It is the second most common type of ichthyosis, with a prevalence of 1/6,000 to 1/2,000 in males and without any racial or geographical differences. The causative gene for XLI is the steroid sulfatase gene (STS), located on Xp22.3. STS deficiency causes an abnormal cholesterol sulfate (CS) accumulation in the stratum corneum (SC). Excess CS induces epidermal permeability barrier dysfunction and scaling abnormalities. This review summarizes XLI's genetic, clinical, and pathological features, pathogenesis, diagnosis and differential diagnoses, and therapeutic perspectives. Further understanding the role of the STS gene pathogenic variants in XLI may contribute to a more accurate and efficient clinical diagnosis of XLI and provide novel strategies for its treatment and prenatal diagnosis.

Hair follicles modulate skin barrier function

Our skin provides a protective barrier that shields us from our environment. Barrier function is typically associated with the interfollicular epidermis; however, whether hair follicles influence this process remains unclear. Here, we utilize a potent genetic tool to probe barrier function by conditionally ablating a quintessential epidermal barrier gene, Abca12, which is mutated in the most severe skin barrier disease, harlequin ichthyosis. With this tool, we deduced 4 ways by which hair follicles modulate skin barrier function. First, the upper hair follicle (uHF) forms a functioning barrier. Second, barrier disruption in the uHF elicits non-cell-autonomous responses in the epidermis. Third, deleting Abca12 in the uHF impairs desquamation and blocks sebum release. Finally, barrier perturbation causes uHF cells to move into the epidermis. Neutralizing IL-17a, whose expression is enriched in the uHF, partially alleviated some disease phenotypes. Altogether, our findings implicate hair follicles as multi-faceted regulators of skin barrier function.

Hair follicles modulate skin barrier function

Our skin provides a protective barrier that shields us from our environment. Barrier function is typically associated with interfollicular epidermis; however, whether hair follicles influence this process remains unclear. Here, we utilize a potent genetic tool to probe barrier function by conditionally ablating a quintessential epidermal barrier gene, Abca12, which is mutated in the most severe skin barrier disease, harlequin ichthyosis. With this tool, we deduced 4 ways by which hair follicles modulate skin barrier function. First, the upper hair follicle (uHF) forms a functioning barrier. Second, barrier disruption in the uHF elicits non-cell autonomous responses in the epidermis. Third, deleting Abca12 in the uHF impairs desquamation and blocks sebum release. Finally, barrier perturbation causes uHF cells to move into the epidermis. Neutralizing Il17a, whose expression is enriched in the uHF, partially alleviated some disease phenotypes. Altogether, our findings implicate hair follicles as multi-faceted regulators of skin barrier function.

Psychosocial impact of severe autosomal recessive congenital ichthyosis

A clinician’s and a patient’s perspective on living with lamellar ichthyosis for over half a century.

Congenital Ichthyosis: Current Approaches to Prenatal Diagnoses

INTRODUCTION

Congenital ichthyosis represents a wide spectrum of diseases. This article reviews prenatal testing for ichthyosis.

METHODS

We used pubmed.ncbi.nlm.nih.gov to search for 38 types of congenital ichthyosis combined with 17 words related to prenatal testing.

RESULTS

Search resulted in 408 publications covering 13 types of ichthyoses and four types of tests.

DISCUSSION

Biochemical testing is diagnostic in trichothiodystrophy, but nonspecific in X-linked ichthyosis and Refsum syndrome. Except in X-linked ichthyosis, biochemical testing requires invasive procedures to obtain fetal skin biopsy, amniocytes, or chorionic villus samples. It is superior to histological and cytological examination of fetal skin biopsy or amniocytes because keratinization occurs later in pregnancy and microscopy cannot differentiate between ichthyosis types. Imaging is more acceptable due to noninvasiveness and routine use, although ultrasonography is operator-dependent, nonspecific, and captures abnormalities at late stage. Molecular tests are described in at-risk pregnancies but testing of free fetal DNA was not described.

Advances in the treatment of autosomal recessive congenital ichthyosis, a look towards the repositioning of drugs

Autosomal recessive congenital ichthyoses (ARCI) are a skin pathology due to genetic causes characterized by a variable degree of desquamation, accompanied by erythema. The degree of symptoms is variable, different altered genes are involved, and the symptoms drastically affect patients' quality of life. Topical treatments are a first-choice strategy due to their ease of application and cost; however, enteral administration of retinoids offers greater efficacy, although with certain limitations. Despite the treatment alternatives, ARCI will persist throughout life, disabling people. Therefore, the search for new treatments always remains necessary. Especially repositioning drugs could be a short-term alternative to new affordable treatments for patients. Taking advantage of extensive knowledge of known drugs or biologics could ensure more accessible and possibly lower-cost treatments. This review briefly and concisely addresses possible repositioning strategies with drugs and biologics for ichthyosis.

Novel peeling skin condition in neonatal Pacific walruses, Saint Lawrence Island, Alaska, USA

We describe here a novel peeling skin condition (PSC) in 2 neonatal Pacific walruses (Odobenus rosmarus subsp. divergens). Macroscopically, calves had various degrees of peeling skin exacerbated by mechanical trauma. Lesions occurred in areas subject to friction: ventrum, fore- and hindflippers, and associated joints. Histopathologic features included pseudocarcinomatous epithelial hyperplasia with orthokeratotic hyperkeratosis. Bacterial cocci were present within the stratum corneum. A few intraepidermal clefts were present. Inflammation, epidermolysis, and vasculopathies were not observed. PCR assays were negative for vesivirus and for Staphylococcus aureus exfoliative and toxic shock syndrome toxins. Tissue samples were cultured and bacteria isolated and identified by MALDI-TOF MS as Carnobacterium maltaromaticum, Psychrobacter phenylpyruvicus, Globicatella sanguinis, Streptococcus phocae, Pseudomonas spp., Rahnella aquatilis, and Escherichia coli. Given the young age of the calves and their clinical presentation, congenital ichthyosis was suspected. No genetic differences were detected for sequenced portions of keratin genes (keratin gene K10) between diseased and normal walrus skin. This rare PSC in neonatal Pacific walruses is recognized as novel by indigenous Alaskan marine mammal hunters of the Bering Strait region. A comprehensive diagnostic work-up of future case materials is needed to characterize the underlying biochemical defect(s).

Otological problems in ichthyosis: A literature review

BACKGROUND

Ichthyoses are a rare group of keratinization disorders characterized by scaling of the skin due to an impaired barrier function. Few studies have addressed ear involvement in patients with ichthyosis, although it is a probably underestimated aspect of the disease.

OBJECTIVE

This study aims to provide an overview of the otological manifestations in ichthyosis and propose specific treatment options.

METHODS

Articles were collected using PubMed, EMBASE, and Web of Science. A total of 53 articles were included in this literature review.

RESULTS

The most common ear problem in patients with ichthyosis is scale accumulation in the ear canals, which can lead to conductive hearing loss and increases the risk of ear infections. Furthermore, some types of ichthyosis are associated with outer ear malformations. Lastly, sensorineural hearing loss is common in syndromic forms of ichthyosis.

CONCLUSIONS

Otological problems are present in all types of ichthyoses and their treatment is challenging. The involvement of ear, nose, and throat specialists in the routine care of ichthyosis patients is essential for early identification and treatment of these manifestations. More research is needed to provide more insight into the otological problems in ichthyosis and to ameliorate treatment options.

Variants in KLK11, affecting signal peptide cleavage of kallikrein-related peptidase 11, cause an autosomal-dominant cornification disorder

BACKGROUND

Mendelian disorders of cornification (MeDOC) are a group of heterogeneous genodermatoses with different genetic bases. The pathogenesis of a substantial group of MeDOC remains to be elucidated.

OBJECTIVES

To identify a new causative gene and the pathogenesis of a previously undescribed autosomal-dominant cornification disorder.

METHODS

Whole-exome sequencing was performed in three families with the novel cornification disorder to identify the disease-causing variants. As the variants were located around the signal peptide (SP) cleavage site of a kallikrein-related peptidase, SP cleavage, subcellular localization and extracellular secretion of the variants were evaluated in eukaryotic overexpression systems by Western blotting or immunocytochemistry. Then the trypsin-like and chymotrypsin-like proteolytic activity of the peptidase and degradation of its catalytic substrate were assayed using the patients' stratum corneum (SC) samples. The morphology of the lamellar bodies and corneodesmosomes (CDs) in the patients' SC was ultrastructurally examined. A mouse model harbouring the equivalent variant was constructed and evaluated histologically.

RESULTS

We identified two heterozygous variants affecting Gly50 in kallikrein-related peptidase (KLK)11 in a familial case and two sporadic cases with the new disorder, which is characterized by early-onset ichthyosiform erythroderma or erythrokeratoderma. KLK11 belongs to the family of kallikrein-related peptidases participating in skin desquamation by decomposing CDs, a process essential for shedding of the SC. In vitro experiments demonstrated that the variants perturbed the SP cleavage of KLK11, leading to subcellular mislocalization and impaired extracellular secretion of the KLK11 Gly50Glu variant. Both trypsin-like and chymotrypsin-like proteolytic activities were significantly decreased in the patients' SC samples. Reduced proteolysis of desmoglein 1 and delayed degeneration of CDs were detected in patients' SC, indicating delayed skin desquamation. Consistently, the patients showed a thickened, dense SC, indicating abnormal skin desquamation. Mice harbouring the homozygous c.131G>A (p.Gly44Glu) Klk11 variant, which is equivalent to KLK11 c.149G>A (p.Gly50Glu) in humans, exhibited hyperkeratosis and abnormal desquamation, partially recapitulating the phenotype.

CONCLUSIONS

We provide evidence that variants at Gly50 affecting the SP cleavage of KLK11 cause a new autosomal-dominant cornification disorder with abnormal desquamation. Our findings highlight the essential role of KLKs in maintaining homeostasis of skin keratinization and desquamation.

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.

ABHD5-A Regulator of Lipid Metabolism Essential for Diverse Cellular Functions

The α/β-Hydrolase domain-containing protein 5 (ABHD5; also known as comparative gene identification-58, or CGI-58) is the causative gene of the Chanarin-Dorfman syndrome (CDS), a disorder mainly characterized by systemic triacylglycerol accumulation and a severe defect in skin barrier function. The clinical phenotype of CDS patients and the characterization of global and tissue-specific ABHD5-deficient mouse strains have demonstrated that ABHD5 is a crucial regulator of lipid and energy homeostasis in various tissues. Although ABHD5 lacks intrinsic hydrolase activity, it functions as a co-activating enzyme of the patatin-like phospholipase domain-containing (PNPLA) protein family that is involved in triacylglycerol and glycerophospholipid, as well as sphingolipid and retinyl ester metabolism. Moreover, ABHD5 interacts with perilipins (PLINs) and fatty acid-binding proteins (FABPs), which are important regulators of lipid homeostasis in adipose and non-adipose tissues. This review focuses on the multifaceted role of ABHD5 in modulating the function of key enzymes in lipid metabolism.

Genetic Etiology of Ichthyosis in Turkish Patients: Nextgeneration Sequencing Identified Seven Novel Mutations

Objective:

Ichthyosis is a clinically heterogeneous group of genodermatoses characterized by widespread drying and scaling of the skin. It is also a genetically heterogeneous disorder, and 67 genes associated with the disease have been identified to date. However, there are still undiscovered genes causing the disease.

Methods:

We investigated 19 Turkish patients from 17 unrelated families using clinical exome sequencing or multigene panel screening.

Results:

Sixteen likely pathogenic or pathogenic variants were detected in 13 unrelated patients. We identified “variant of unknown significance” alteration in only one patient. Seven novel variants were identified in ABCA12, ALOX12B, and ALOXE3. The most commonly mutated gene was TGM1, followed by ABCA12 and ALOX12B.

Conclusions:

Because of the wide genetic variability of ichthyosis, it is difficult to diagnose the disease quickly and definitively. The clinical use of next-generation sequencing (NGS) methodologies is beneficial in the diagnostic approach to ichthyosis and genetic counseling. This study highlights the underlying molecular cause of ichthyosis by determining the mutational spectrum in a cohort of 19 patients. This study is the first and largest research from Turkey using NGS that highlights all ichthyosis subtypes.

Proposal for a 6-step-approach for differential diagnosis of neonatal erythroderma

The broad differential diagnosis of neonatal erythroderma often poses a diagnostic challenge. Mortality of neonatal erythroderma is high due to complications of the erythroderma itself and the occasionally severe and life-threatening underlying disease. Early correct recognition of the underlying cause leads to better treatment and prognosis. Currently, neonatal erythroderma is approached by a case by case basis. The purpose of this scoping review was to develop a diagnostic approach in neonatal erythroderma. After a systematic literature search in Embase (January 1990 - May 2020, 74 cases of neonatal erythroderma were identified, and 50+ diagnoses could be extracted. Main causes were the ichthyoses (40%) and primary immunodeficiencies (35%). Congenital erythroderma was present in 64% (47/74) of the cases, predominantly with congenital ichthyosis (11/11; 100%), Netherton syndrome (12/14, 86%), and Omenn syndrome (11/23, 48%). Time until diagnosis ranged from 102 days to 116 days for cases of non-congenital erythroderma and congenital erythroderma respectively. Among the 74 identified cases a total of 17 patients (23%) died within a mean of 158 days and were related to Omenn syndrome (35%), graft versus host disease (67%), and Netherton syndrome (18%). Disease history and physical examination are summarized in this paper. Age of onset and a collodion membrane can help to narrow the differential diagnoses. Investigations of blood, histology, hair analysis, genetic analysis and clinical imaging are summarized and discussed. A standard blood investigation is proposed and the need for skin biopsies with Lympho-Epithelial Kazal-Type related Inhibitor-staining is highlighted. Overall, this review shows that diagnostic procedures narrow the differential diagnosis in neonatal erythroderma. A 6-step flowchart for the diagnostic approach for neonatal erythroderma during the first month of life is proposed. The approach was made with the support of expert leaders from international multidisciplinary collaborations in the European Reference Network Skin-subthematic group Ichthyosis.

ABHD5 frameshift deletion in Golden Retrievers with ichthyosis

Ichthyoses are hereditary skin disorders characterized by the formation of scales and defects in the outermost layer of the epidermis. In dogs, at least six different breed-specific ichthyoses including a relatively common PNPLA1-related autosomal recessive ichthyosis in Golden Retrievers are known. In this study, we investigated 14 Golden Retrievers with scales that were not homozygous for the mutant PNPLA1 allele suggesting a genetically distinct new form of ichthyosis. Histopathological examinations showed lamellar, orthokeratotic hyperkeratosis, and mildly hyperplastic epidermis that led to the diagnosis of a nonepidermolytic ichthyosis. Combined linkage and homozygosity mapping in 14 cases and 30 nonaffected family members delimited a critical interval of ∼12.7 Mb on chromosome 23. Whole-genome sequencing of an affected dog revealed a single protein-changing variant within this region that was not present in 795 control genomes. The identified variant is a 14 bp deletion in the ABHD5 gene (c.1006_1019del), leading to a frameshift and altering the last 14 codons p.(Asp336Serfs*6). The genotypes at this variant showed perfect cosegregation with the ichthyosis phenotype in a large family comprising 14 cases and 72 controls. ABHD5 encodes an acyltransferase required for lipid metabolism. In humans, variants in ABHD5 cause Chanarin-Dorfman syndrome, a neutral lipid storage disease with ichthyosis. Our data in dogs together with the knowledge on the effects of ABHD5 variants in humans strongly suggest ABHD5:c.1006_1019del as candidate causative genetic variant for a new canine form of ichthyosis, which we propose to designate as Golden Retriever ichthyosis type 2 (ICH2).

Analysis of the structure and function of the epidermal barrier in patients with ichthyoses - clinical and electron microscopical investigations

BACKGROUND

Ichthyoses are pathogenetically characterised by a pronounced disorder of the epidermal barrier. Clinically, hyperkeratosis, severe scaling and erythroderma are present on the entire integument. The time-consuming therapy includes daily baths and the application of skin care products to restore the epidermal barrier.

OBJECTIVES AND METHODS

To enhance the knowledge about the structure and function of the epidermal barrier in ichthyoses, we conducted clinical, biophysical and electron microscopical measurements on 46 patients with ichthyoses, including autosomal recessive ichthyoses, keratinopathic ichthyoses, X-chromosomal recessive ichthyosis and Netherton syndrome.

RESULTS

The patients displayed a significantly decreased skin hydration along with unexpectedly low transepidermal waterloss values. Electron microscopical examinations demonstrated a severe occlusion of the epidermis by lipid remnants of skin care products in the stratum corneum. We found decreased intercellular lipid lamellae and an increased undulation of the corneocyte membrane of all ichthyoses, mostly pronounced in Netherton syndrome. The lipid profiles of ichthyoses showed decreased esterified Ω-hydroxy-sphingosine (EOS) ceramide levels.

CONCLUSIONS

The results demonstrate the extent of the epidermal barrier disruption in ichthyoses. In combination with the knowledge about pathogenetic causes, individually improved therapeutic options can be derived from our results. In the future, the analyses of the organisation of intercellular lipid lamellae and corneocyte membrane undulation will enable improved investigations of the epidermal barrier in ichthyoses and may be used to study and evaluate possible effects of topical skin preparations.

Pili Torti: A Feature of Numerous Congenital and Acquired Conditions

Pili torti is a rare condition characterized by the presence of the hair shaft, which is flattened at irregular intervals and twisted 180° along its long axis. It is a form of hair shaft disorder with increased fragility. The condition is classified into inherited and acquired. Inherited forms may be either isolated or associated with numerous genetic diseases or syndromes (e.g., Menkes disease, Björnstad syndrome, Netherton syndrome, and Bazex-Dupré-Christol syndrome). Moreover, pili torti may be a feature of various ectodermal dysplasias (such as Rapp-Hodgkin syndrome and Ankyloblepharon-ectodermal defects-cleft lip/palate syndrome). Acquired pili torti was described in numerous forms of alopecia (e.g., lichen planopilaris, discoid lupus erythematosus, dissecting cellulitis, folliculitis decalvans, alopecia areata) as well as neoplastic and systemic diseases (such as cutaneous T-cell lymphoma, scalp metastasis of breast cancer, anorexia nervosa, malnutrition, cataracts, and chronic graft-vs.-host disease). The condition may also be induced by several drugs (epidermal growth factor receptor inhibitors, oral retinoids, sodium valproate, and carbamide perhydrate). The diagnosis of pili torti is based on trichoscopic or microscopic examination. As pili torti is a marker of numerous congenital and acquired disorders, in every case, the search for the signs of underlying conditions is recommended.

Ichthyosis (concept, pathohistology, clinical picture, treatment)

Ichthyosis is a skin disease that is hereditary, has pronounced symptoms in the form of a violation of the skin, and the presence of formations resembling fish scales. It is possible to distinguish different approaches to the definition of ichthyosis, based on the modern study of this issue. Ichthyosis is classified by type: congenital and acquired. Congenital ichthyosis has its own classification depending on the manifestation of changes in the skin, the course of the disease, concomitant pathologies. Congenital ichthyosis is divided into ordinary (vulgar autosomal dominant, simple) ichthyosis, lamellar ichthyosis (dry ichthyosiform erythroderma, "collodion child", lamellar ichthyosis), X-linked ichthyosis (ichthyosis associated with the X chromosome, blackening ichthyosis), congenital bullous ichthyosiform erythroderma (erythroderma Broca's disease, ichthyosiform epidermolytic hyperkeratosis), fetal ichthyosis (intrauterine ichthyosis, universal hyperkeratosis, "Harlequin fetus", congenital keratosis), other congenital ichthyosis. Ichthyosiform conditions (the so-called acquired ichthyosis) are divided into symptomatic, age-related (senile), discoid ichthyosis. The causes of acquired ichthyosis can be various diseases, taking medications, improper skin care, unbalanced nutrition. Each form of ichthyosis differs by the type of inheritance, prevalence in the population, clinical picture, verified by histological examination of skin biopsies and electron microscopic examination of the skin. It may be accompanied by seasonality of exacerbation of the clinical picture, association with other diseases (allergic, diseases of the gastrointestinal tract, congenital malformations). There is no specific treatment for ichthyosis. In systemic therapy, derivatives of vitamin A are used, keratolytics, as well as moisturizing and emollient agents are used for external treatment. The use of therapeutic baths, general ultraviolet irradiation is effective.

Ichthyosis: case report in a Colombian man with genetic alterations in ABCA12 and HRNR genes

BACKGROUND

Ichthyosis is a heterogeneous group of diseases caused by genetic disorders related to skin formation. They are characterized by generalized dry skin, scaling, hyperkeratosis and frequently associated with erythroderma. Among its different types, harlequin ichthyosis (HI) stands out due to its severity. HI is caused by mutations in the ABCA12 gene, which encodes essential proteins in epidermal lipid transport, and it helps maintain the homeostasis of the stratum corneum of the epidermis. However, due to the wide spectrum of genetic alterations that can cause ichthyosis, holistic medical care, and genetic studies are required to improve the diagnosis and outcomes of these diseases.

CASE PRESENTATION

Here, we presented the case of a 19 years old male patient who was a premature infant and exhibited clinical features consistent with HI, including bright yellow hyperkeratotic plates with erythematous fissures that covered his entire body like a collodion baby. Currently, he exhibited erythroderma, photosensitivity, ectropion, auricular pavilion alterations, and musculoskeletal disorders, such as equinovarus feet, fingers, hands, and hypoplastic feet with contractures in flexion and marked difficulty in fine motor skills. In addition, he presented dyschromatopsia, Achilles reflex hyporeflexia, slight speech, dental alteration and deficient cognitive performance. After the genetic sequencing, variants were found in ABCA12 and HRNR which are related to several skin diseases, including ichthyosis.

CONCLUSIONS

Although in clinical practice, ichthyosis is a common entity, a severe type of ichthyosis is presented, highlighting the importance of appropriate genetic diagnosis, given the broad spectrum of genetic alterations with similar phenotypic and clinical characteristics. These pathologies must be known to guarantee initial support measures to prevent complications and offer multidisciplinary management to those patients.

Novel Homozygous Mutations in the Genes TGM1, SULT2B1, SPINK5 and FLG in Four Families Underlying Congenital Ichthyosis

Background: Ichthyoses are a large group of hereditary cornification disorders, which are both clinically and etiologically heterogeneous and affect mostly all the skin surface of the patients. Ichthyosis has its origin in an ancient Greek word “ichthys” meaning fish, this is because the ichthyosis patients have dry, thickened, and scaly skin. There is an excess accumulation of epidermal cells resulting in the appearance of continuous and widespread scales on the body. There are many varieties of ichthyosis with a broad spectrum of intensity, severity, and associated symptoms, most of them are extremely rare. Ichthyosis vulgaris is the most frequently occurring type of ichthyoses. Method: The present study consists of four Pakistani ichthyosis families (A, B, C, and D). Whole exome sequencing (WES) approach was used to identify the pathogenic sequence variants in probands. The segregation of these variants in other participants was confirmed by Sanger sequencing. Results: Total four variants including, two splice site (TGM1: c.2088 + 1G > A) and (SPINK5: c.882 + 1G > T), a missense (SULT2B1: c.419C > T; p. Ala140Val), and a nonsense (FLG: c.6109C > T; p. Arg2037Ter) variant were identified in families A, C, B, and D, respectively, as causative mutations responsible for ichthyosis in these families. Conclusion: Our study unravels the molecular etiology of the four Pakistani ichthyosis families and validates the involvement of TGM1, SULT2B1, SPINK5, and FLG, in the etiology of different forms of ichthyosis. In addition, this study also aims to give a detailed clinical report of the studied ichthyosis families.

Experimental Models for the Study of Hereditary Cornification Defects

Ichthyoses comprise a broad spectrum of keratinization disorders due to hereditary defects of cornification. Until now, mutations in more than 50 genes, mostly coding for structural proteins involved in epidermal barrier formation, have been identified as causes for different types of these keratinization disorders. However, due to the high heterogeneity and difficulties in the establishment of valid experimental models, research in this field remains challenging and translation of novel findings to clinical practice is difficult. In this review, we provide an overview of existing models to study hereditary cornification defects with focus on ichthyoses and palmoplantar keratodermas.

Sarcoptic mange severity is associated with reduced genomic variation and evidence of selection in Yellowstone National Park wolves (Canis lupus)

Population genetic theory posits that molecular variation buffers against disease risk. Although this "monoculture effect" is well supported in agricultural settings, its applicability to wildlife populations remains in question. In the present study, we examined the genomics underlying individual-level disease severity and population-level consequences of sarcoptic mange infection in a wild population of canids. Using gray wolves (Canis lupus) reintroduced to Yellowstone National Park (YNP) as our focal system, we leveraged 25 years of observational data and biobanked blood and tissue to genotype 76,859 loci in over 400 wolves. At the individual level, we reported an inverse relationship between host genomic variation and infection severity. We additionally identified 410 loci significantly associated with mange severity, with annotations related to inflammation, immunity, and skin barrier integrity and disorders. We contextualized results within environmental, demographic, and behavioral variables, and confirmed that genetic variation was predictive of infection severity. At the population level, we reported decreased genome-wide variation since the initial gray wolf reintroduction event and identified evidence of selection acting against alleles associated with mange infection severity. We concluded that genomic variation plays an important role in disease severity in YNP wolves. This role scales from individual to population levels, and includes patterns of genome-wide variation in support of the monoculture effect and specific loci associated with the complex mange phenotype. Results yielded system-specific insights, while also highlighting the relevance of genomic analyses to wildlife disease ecology, evolution, and conservation.

Mutation in ALOX12B likely cause of POI and also ichthyosis in a large Iranian pedigree

Premature ovarian insufficiency (POI) is a clinically and etiologically heterogeneous disorder characterized by menstrual irregularities and elevated levels of FSH before age of 40 years. Genetic anomalies are among the recognized causes of POI. Here, we aimed to identify the genetic cause of POI in an inbred pedigree with nine POI and two ichthyosis-affected members. Inheritance of POI and ichthyosis were, respectively, dominant and recessive. Reproduction-related information and measurements of relevant hormones were obtained. Genetic studies included homozygosity mapping, linkage analysis, exome sequencing, and screening of candidate variants. A mutation within ALOX12B, which is a known ichthyosis causing gene, was identified as cause of ichthyosis. ALOX12B encodes a protein involved in steroidogenesis and lipid metabolism. Considering the importance of steroidogenesis in reproduction functions, the possibility that the ALOX12B mutation is also cause of POI was considered. Screenings showed that the mutation segregated with POI status. Linkage analysis with respect to POI identified a single strongly linked locus (LOD > 3) that includes ALOX12B. Exome sequencing on POI-affected females identified the mutation in ALOX12B and also a sequence variation in SPNS2 within the linked locus. A possible contribution of the SPNS2 variation to POI was not strictly ruled out, but various data presented in the text including reported association of variations in related gene ALOX12 with menopause-age and role of ALOX12B in atretic bovine follicle formation argue in favor of ALOX12B. It is, therefore, concluded that the mutation in ALOX12B is the likely cause of POI in the pedigree.

Spectrum of ichthyoses in an Austrian ichthyosis cohort from 2004 to 2017

BACKGROUND

Ichthyoses are a heterogeneous disease group, which makes clinical classification challenging. An ichthyosis cohort at a center for genodermatoses is presented in detail.

PATIENTS AND METHODS

Patients with clinically and/or genetically confirmed ichthyosis seen from 2004 to 2017 and listed in a database were included. Disease onset, phenotype, histology, comorbidities and family history were described in detail. In genetically tested patients, the prevalence of various ARCI genes, ARCI phenotypes and syndromic ichthyoses, as well as genotype-phenotype correlation and year/method of genetic testing was assessed.

RESULTS

Of all 198 patients who were included in the cohort, 151 were genetically tested. 81 had ichthyosis vulgaris, 43 X-linked ichthyosis, 38 autosomal recessive congenital ichthyosis (ARCI), 9 keratinopathic ichthyosis (KPI) and one exfoliative ichthyosis. 26 individuals suffered from syndromic ichthyoses. A good genotype-phenotype correlation was observed for common ichthyoses and KPI; the correlation was less good in syndromic ichthyoses. In 91 % of ARCI patients an accurate diagnosis was obtained by genetic testing. In only 33 % of syndromic ichthyoses was the definitive diagnosis suspected before genetic testing, which revealed a causative mutation in 86 % of cases.

CONCLUSION

This study describes the spectrum of ichthyoses in a center of expertise and shows that genetic testing should become a diagnostic standard for this disease group.

Expanding the Clinical and Genetic Spectra of Primary Immunodeficiency-Related Disorders With Clinical Exome Sequencing: Expected and Unexpected Findings

Primary immunodeficiencies (PIDs) refer to a clinically, immunologically, and genetically heterogeneous group of over 350 disorders affecting development or function of the immune system. The increasing use of next-generation sequencing (NGS) technology has greatly facilitated identification of genetic defects in PID patients in daily clinical practice. Several NGS approaches are available, from the unbiased whole exome sequencing (WES) to specific gene panels. Here, we report on a 3-year experience with clinical exome sequencing (CES) for genetic diagnosis of PIDs. We used the TruSight One sequencing panel, which includes 4,813 disease-associated genes, in 61 unrelated patients (pediatric and adults). The analysis was done in 2 steps: first, we focused on a virtual PID panel and then, we expanded the analysis to the remaining genes. A molecular diagnosis was achieved in 19 (31%) patients: 12 (20%) with mutations in genes included in the virtual PID panel and 7 (11%) with mutations in other genes. These latter cases provided interesting and somewhat unexpected findings that expand the clinical and genetic spectra of PID-related disorders, and are useful to consider in the differential diagnosis. We also discuss 5 patients (8%) with incomplete genotypes or variants of uncertain significance. Finally, we address the limitations of CES exemplified by 7 patients (11%) with negative results on CES who were later diagnosed by other approaches (more specific PID panels, WES, and comparative genomic hybridization array). In summary, the genetic diagnosis rate using CES was 31% (including a description of 12 novel mutations), which rose to 42% after including diagnoses achieved by later use of other techniques. The description of patients with mutations in genes not included in the PID classification illustrates the heterogeneity and complexity of PID-related disorders.

[Genetics and dermatology]

Many types of genodermatosis exist, with numerous modes of transmission. The development of molecular genetic methods, in particular the most recent sequencing techniques, can be used to identify an increasing number of genes involved in these forms of genodermatosis while providing confirmation or more details regarding clinical diagnosis. Thanks to this approach, it is possible to determine risk of recurrence and to formulate an antenatal strategy. These technologies have led to improved molecular definition and to a better understanding of the physiopathological mechanisms involved in different genodermatoses such as bullous epidermolysis, keratinisation disorders, pigmentation disorders, potentially tumoral conditions, and epidermal and pilar dysplasia. The large amount of information provided by high-throughput sequencing makes it possible to study modifying genes as well as genotype-phenotype correlations. However, this genetic information in its turn poses problems of interpretation and of control of the resulting data. The use of genetics in dermatology for the purposes of diagnosis or research requires a consultation to provide patients with information regarding the genetic tests involved and the potential consequences thereof for them and their families. Furthermore, with pangenomic approaches there is a higher probability of fortuitous discovery of abnormalities such as variants associated with risks predisposing to cancer or neurodegenerative disease. Collaboration between dermatologists and geneticists enables optimisation of patient management in terms of diagnosis and genetic counselling in the event of such rare diseases. Therapeutic applications are beginning to be developed. The scope of therapeutic application includes gene therapy, replacement therapy (enzyme therapy) and targeted therapy.

Unknown mutations and genotype/phenotype correlations of autosomal recessive congenital ichthyosis in patients from Saudi Arabia and Pakistan

BACKGROUND

Autosomal recessive congenital ichthyosis (ARCI) is a genetically and phenotypically heterogeneous skin disease, associated with defects in the skin permeability barrier. Several but not all genes with underlying mutations have been identified, but a clear correlation between genetic causes and clinical picture has not been described to date.

METHODS

Our study included 19 families from Saudi Arabia, Yemen, and Pakistan. All patients were born to consanguineous parents and diagnosed with ARCI. Mutations were analyzed by homozygosity mapping and direct sequencing.

RESULTS

We have detected mutations in all families in five different genes: TGM1, ABCA12, CYP4F22, NIPAL4, and ALOXE3. Five likely pathogenic variants were unknown so far, a splice site and a missense variant in TGM1, a splice site variant in NIPAL4, and missense variants in ABCA12 and CYP4F22. We attributed TGM1 and ABCA12 mutations to the most severe forms of lamellar and erythematous ichthyoses, respectively, regardless of treatment. Other mutations highlighted the presence of a phenotypic spectrum in ARCI.

CONCLUSION

Our results contribute to expanding the mutational spectrum of ARCI and revealed new insights into genotype/phenotype correlations. The findings are instrumental for a faster and more precise diagnosis, a better understanding of the pathophysiology, and the definition of targets for more specific therapies for ARCI.

ABHD5 stimulates PNPLA1-mediated ω-O-acylceramide biosynthesis essential for a functional skin permeability barrier

Mutations in the genes coding for patatin-like phospholipase domain-containing 1 (PNPLA1) and α/β-hydrolase domain-containing 5 (ABHD5), also known as comparative gene identification 58, are causative for ichthyosis, a severe skin barrier disorder. Individuals with mutations in either of these genes show a defect in epidermal ω-O-acylceramide (AcylCer) biosynthesis, suggesting that PNPLA1 and ABHD5 act in the same metabolic pathway. In this report, we identified ABHD5 as a coactivator of PNPLA1 that stimulates the esterification of ω-hydroxy ceramides with linoleic acid for AcylCer biosynthesis. ABHD5 interacts with PNPLA1 and recruits the enzyme to its putative triacylglycerol substrate onto cytosolic lipid droplets. Conversely, alleles of ABHD5 carrying point mutations associated with ichthyosis in humans failed to accelerate PNPLA1-mediated AcylCer biosynthesis. Our findings establish an important biochemical function of ABHD5 in interacting with PNPLA1 to synthesize crucial epidermal lipids, emphasizing the significance of these proteins in the formation of a functional skin permeability barrier.

A successful case of neoadjuvant chemotherapy and radical hysterectomy during pregnancy for advanced uterine cervical cancer accompanied by neonatal erythroderma

Recent reports showed that neoadjuvant chemotherapy (NAC) has been successfully applied to treat advanced uterine cervical cancers during pregnancy. However, its side effects on the fetus remain unclear. Here, we report a 33-year-old primipara who underwent four courses of NAC therapy, paclitaxel and cisplatin, from 17 to 27 weeks of gestation due to uterine cervical cancer stage IB2. At 31 weeks of gestation, cesarean section and radical hysterectomy were performed, and a female baby weighing 1446 g was born. Although pre- and postnatal courses were uneventful, neonatal erythroderma over the entire body was observed just after delivery. The pathological diagnosis was ichthyosiform erythroderma, which was later demonstrated to be keratitis-ichthyosis-deafness syndrome, by exome sequencing analysis. Although her skin disorder was consistent with keratitis-ichthyosis-deafness syndrome, the skin condition gradually improved after delivery. These findings suggest that NAC therapy during pregnancy might cause or exacerbate systemic skin lesions in the fetus/neonate.

Inherited Nonsyndromic Ichthyoses: An Update on Pathophysiology, Diagnosis and Treatment

Hereditary ichthyoses are due to mutations on one or both alleles of more than 30 different genes, mainly expressed in the upper epidermis. Syndromic as well as nonsyndromic forms of ichthyosis exist. Irrespective of etiology, virtually all types of ichthyosis exhibit a defective epidermal barrier that constitutes the driving force for hyperkeratosis, skin scaling, and inflammation. In nonsyndromic forms, these features are most evident in severe autosomal recessive congenital ichthyosis (ARCI) and epidermolytic ichthyosis, but to some extent also occur in the common type of non-congenital ichthyosis. A correct diagnosis of ichthyosis-essential not only for genetic counseling but also for adequate patient information about prognosis and therapeutic options-is becoming increasingly feasible thanks to recent progress in genetic knowledge and DNA sequencing methods. This paper reviews the most important aspects of nonsyndromic ichthyoses, focusing on new knowledge about the pathophysiology of the disorders, which will hopefully lead to novel ideas about therapy.

Ocular manifestations, complications and management of congenital ichthyoses: a new look

Congenital ichthyoses (CI) are rare genetic skin keratinisation diseases characterised by generalised scaling and a variable degree of erythema and hyperkeratosis. Ocular involvement includes the eyelids, conjunctiva and all layers of the cornea. Ophthalmic input should include regular slit lamp review with the primary aim to prevent a corneal epithelial defect, secondary bacterial infection, scarring or perforation. This review highlights the current literature regarding ophthalmic findings and management of CI.

Role of the liver X receptors in skin physiology: Putative pharmacological targets in human diseases

Liver X receptors (LXRs) are members of the nuclear receptor superfamily that have been shown to regulate various physiological functions such as lipid metabolism and cholesterol homeostasis. Concordant reports have elicited the possibility to target them to cure many human diseases including arteriosclerosis, cancer, arthritis, and diabetes. The high relevance of modulating LXR activities to treat numerous skin diseases, mainly those with exacerbated inflammation processes, contrasts with the lack of approved therapeutic use. This review makes an assessment to sum up the findings regarding the physiological roles of LXRs in skin and help progress towards the therapeutic and safe management of their activities. It focuses on the possible pharmacological targeting of LXRs to cure or prevent selected skin diseases.

Morphological alterations in two siblings with autosomal recessive congenital ichthyosis associated with CYP4F22 mutations

Autosomal recessive congenital ichthyosis (ARCI) caused by mutations in CYP4F22 is very rare. CyP4F22, a protein of the cytochrome-P450 family 4, encodes an epidermal ω-hydroxylase decisive in the formation of acylceramides, which is hypothesized to be crucial for skin-barrier function. We report a girl with consanguineous parents presenting as collodion baby with contractures of the great joints and palmoplantar hyperlinearity. In the course of the disease she developed fine scaling of the skin with erythroderma, the latter disappearing until the age of 6 months. Her sister showed a generalized fine-scaling phenotype, and, interestingly, was born without a collodion membrane. The analysis of all known candidate genes for ARCI in parallel with a next-generation sequencing approach using a newly designed dermatogenetics gene panel revealed a previously unknown homozygous splice-site mutation c.549+5G>C in CYP4F22 in both girls, confirming the diagnosis of ARCI. Ultrastructural analysis by transmission electron microscopy in both patients showed epidermal hyperplasia, orthohyperkeratosis with persistence of corneodesmosomes into the outer stratum corneum layers, fragmented and disorganized lamellar lipid bilayers, which could be ascribed to inhomogeneous lamellar body secretion, as well as lamellar body and lipid entombment in the corneocytes. These findings correlated with increased transepidermal water loss on the functional level. For the first time, we report a collodion baby phenotype and epidermal barrier impairment in CyP4F22-deficient epidermis at both the ultrastructural and functional level, and corroborate the importance of CyP4F22 for epidermal maturation and barrier function.

Gene-Targeted Next Generation Sequencing Identifies PNPLA1 Mutations in Patients with a Phenotypic Spectrum of Autosomal Recessive Congenital Ichthyosis: The Impact of Consanguinity

Autosomal recessive congenital ichthyosis is a heterogeneous group of disorders associated with mutations in at least nine distinct genes. To ascertain the molecular basis of ichthyosis patients in Iran, a country of approximately 80 million people with a high prevalence of customary consanguineous marriages, we have developed a gene-targeted next generation sequencing array consisting of 38 genes reported in association with ichthyosis phenotypes. In a subset of nine extended consanguineous families, we found homozygous missense mutations in the PNPLA1 gene, six of them being distinct and, to our knowledge, previously unpublished. This gene encodes an enzyme with lipid hydrolase activity, important for development and maintenance of the barrier function of the epidermis. These six mutations, as well as four previously published mutations, reside exclusively within the patatin-like subdomain of PNPLA1 containing the catalytic site. The mutations clustered around the active center of the enzyme or resided at the surface of the protein possibly involved in the protein-protein interactions. Clinical features of the patients showed considerable intra- and interfamilial heterogeneity. Knowledge of the specific mutations allows identification of heterozygous carriers, assisting in genetic counseling, prenatal testing, and preimplantation genetic diagnosis in extended families at risk of recurrence of this disorder, the incidence of which is significantly increased in consanguineous marriages.

PNPLA1 Deficiency in Mice and Humans Leads to a Defect in the Synthesis of Omega-O-Acylceramides

Mutations in PNPLA1 have been identified as causative for autosomal recessive congenital ichthyosis in humans and dogs. So far, the underlying molecular mechanisms are unknown. In this study, we generated and characterized PNPLA1-deficient mice and found that PNPLA1 is crucial for epidermal sphingolipid synthesis. The absence of functional PNPLA1 in mice impaired the formation of omega-O-acylceramides and led to an accumulation of nonesterified omega-hydroxy-ceramides. As a consequence, PNPLA1-deficient mice lacked a functional corneocyte-bound lipid envelope leading to a severe skin barrier defect and premature death of newborn animals. Functional analyses of differentiated keratinocytes from a patient with mutated PNPLA1 demonstrated an identical defect in omega-O-acylceramide synthesis in human cells, indicating that PNPLA1 function is conserved among mammals and indispensable for normal skin physiology. Notably, topical application of epidermal lipids from wild-type onto Pnpla1-mutant mice promoted rebuilding of the corneocyte-bound lipid envelope, indicating that supplementation of ichthyotic skin with omega-O-acylceramides might be a therapeutic approach for the treatment of skin symptoms in individuals affected by omega-O-acylceramide deficiency.

Epidermal barrier in hereditary ichthyoses, atopic dermatitis, and psoriasis

Several skin disorders are associated with impaired skin barrier function. Primary dysfunction is caused by monogenic defects in key components of the epidermis (for example ichthyoses). Secondary barrier impairment occurs in inflammatory dermatoses marked by disturbed epidermal homeostasis (eczema, psoriasis, etc.). In these disorders, inflammation impedes the synthesis or maintenance of skin barrier components. Recent evidence suggests a combination of primary and secondary barrier dysfunction in atopic dermatitis and, to a lesser extent, also in psoriasis. In the future, subtypes of atopic dermatitis may likely be defined, in which one or the other is prevalent.

Management of Epidermolytic Ichthyosis in the Newborn

Epidermolytic ichthyosis (EI) is a rare autosomal dominant genodermatosis that presents at birth as a bullous disease, followed by a lifelong ichthyotic skin disorder. Essentially, it is a defective keratinization caused by mutations of keratin 1 (KRT1) or keratin 10 (KRT10) genes, which lead to skin fragility, blistering, and eventually hyperkeratosis. Successful management of EI in the newborn period can be achieved through a thoughtful, directed, and interdisciplinary or multidisciplinary approach that encompasses family support. This condition requires meticulous care to avoid associated morbidities such as infection and dehydration. A better understanding of the disrupted barrier protection of the skin in these patients provides a basis for management with daily bathing, liberal emollients, pain control, and proper nutrition as the mainstays of treatment. In addition, this case presentation will include discussions on the pathophysiology, complications, differential diagnosis, and psychosocial and ethical issues.

Collodion Baby with TGM1 gene mutation

Collodion baby (CB) is normally diagnosed at the time of birth and refers to a newborn infant that is delivered with a lambskin-like membrane encompassing the total body surface. CB is not a specific disease entity, but is a common phenotype in conditions like harlequin ichthyosis, lamellar ichthyosis, nonbullous congenital ichthyosiform erythroderma, and trichothiodystrophy. We report a CB that was brought to our department and later diagnosed to have TGM1 gene c.984+1G>A mutation. However, it could not be ascertained whether the infant had lamellar ichthyosis or congenital ichthyosiform erythroderma (both having the same mutation). The infant was lost to follow-up.