Ichthyoses – Part 1: Differential diagnosis of vulgar ichthyoses and therapeutic options

Ichthyoses are a group of genetic disorders with defective cornification, clinically characterized by scaling of the skin. Additionally, distinctive cutaneous inflammation can often be observed. For most of the patients these diseases lead to a significant restriction in quality of life. The diagnostic criteria include clinical and histological findings, often confirmed by specialized tests. Because many of the ichthyoses are extremely rare, their accurate diagnosis is often carried out in specialized centers. We summarize isolated vulgar and congenital ichthyoses both with and without associated symptoms and focus on the common genetic changes and their clinical phenotype. Specific therapies are still not available for most of these genetic disorders. The use of different topical agents (e. g. urea, retinoids and salicylic acid) and baths followed by mechanical keratolysis (sometimes in combination with systemic retinoids) reduce symptoms. Patients with uncommon congenital ichthyoses often benefit from interdisciplinary management which involves specialized dermatological centers. In this first part of the paper the vulgar ichthyoses as well as the diagnostic and therapeutic options are discussed. The second part focuses on the congenital ichthyoses and their differential diagnosis.     

Ichthyoses: differential diagnosis and molecular genetics

Ichthyoses are a heterogeneous group of cornification disorders characterized by a generalized scaling of the skin. Common types such as ichthyosis vulgaris and X-linked recessive ichthyosis manifest after birth. In contrast, rare congenital ichthyoses are inherited diseases, which at birth typically present collodion membranes or ichthyosiform erythroderma. Syndromic ichthyoses display a variety of outstanding associated non-cutaneous symptoms. Because of their rarity these disorders often pose a diagnostic challenge for the clinician. This review discusses a broad spectrum of 13 isolated types of ichthyoses, 11 different syndromes with associated ichthyosis and four related cornification disorders. The clinical, ultrastructural and biochemical characteristics are described along with the different molecular causes of ichthyosis. Special attention is given to lamellar ichthyosis and non-bullous congenital ichthyosiform erythroderma. The different pathomechanisms causing ichthyosis provide a fascinating insight into the role of various proteins, enzymes, lipids and metabolic pathways involved in terminal epidermal differentiation/keratinisation.     

Ichthyosis

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 nonsyndromic 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.     

Ichthyoses in everyday practice: management of a rare group of diseases

Ichthyoses comprise a heterogeneous group of hereditary disorders of keratinization characterized by a highly varied clinical picture. A distinction is made between common hereditary ichthyoses (ichthyosis vulgaris and X‐linked ichthyosis), which usually manifest themselves in the first year of life, and rare, sometimes severe congenital ichthyoses. Patients with very mild symptoms often do not even realize they have ichthyosis. The diagnosis is usually based on clinical evaluation. Molecular genetic testing as well as histological and electron microscopic studies may aid in confirming the diagnosis. Mapping a family tree is also diagnostically useful. Besides skin manifestations, important aspects of the clinical examination and history include disease onset, presence of a collodion membrane at birth as well as the presence of hair anomalies and extracutaneous signs and symptoms. Rigorous hydration of the skin (several times a day) and balneotherapy are the mainstay of ichthyosis treatment. For patients with severe disease, systemic acitretin treatment should be considered on a case‐by‐case basis. While ichthyoses are generally limited to the skin, there are syndromic forms that may affect other organs and that require interdisciplinarity cooperation. Although ichthyoses remain incurable, they can be managed well with symptomatic treatment. However, such treatment is frequently time consuming and expensive. In the future, novel therapeutic approaches might include enzyme replacement and gene therapies as well as antiinflammatory drugs.     

Ichthyosen und verwandte Verhornungsstörungen

This review concerns ichthyoses and related keratinization disorders. These are rare genetic skin diseases which are associated with marked scaling, often considerable cutaneous inflammation and a severe disease burden both physically as well as psychosomatically. The review briefly discusses how to establish a clinical diagnosis, how to provide genetic counseling for the patient and their family and how to best manage such diseases. Particular emphasis is given to the new possibilities in diagnosis and treatment opened by the recently established network for ichthyoses and related keratinization disorders (NIRK). This network is funded by the German Ministry for Education and Research and aims to integrate research efforts into disease mechanisms and to spread and transfer knowledge about these diseases to achieve better clinical care for the patients.     

Recent Advances in the Genetics and Management of Harlequin Ichthyosis

Harlequin ichthyosis (HI) is the most severe and devastating form of the autosomal recessive congenital ichthyoses (ARCIs). Mutations in the ABCA12 gene result in disruption of intercellular lipid deposition in the stratum corneum and a major skin barrier defect. Patients present at birth, often premature, with cutaneous thick, yellow, hyperkeratotic plates with deep erythematous fissures, causing a typical facial appearance. Harlequin ichthyosis has often been considered to be fatal, and management tends to be palliative, but follow‐up of 45 affected infants has shown that with good neonatal care and early introduction of oral retinoids, survival rates are improving. Because ABCA12 mutations have been identified, known carriers are able to undergo preventative preimplantation and prenatal genetic testing. Experimental studies have shown recovery of lipid secretion in lamellar granules using corrective gene therapy. Further research is needed to develop alternative therapies to retinoids in HI.     

Harlequin ichthyosis and other autosomal recessive congenital ichthyoses: the underlying genetic defects and pathomechanisms

Autosomal recessive congenital ichthyoses (ARCI) include several severe subtypes including harlequin ichthyosis (HI), lamellar ichthyosis and non-bullous congenital ichthyosiform erythroderma. Patients with these severe types of ichthyoses frequently show severe hyperkeratosis and scales over a large part of the body surface form birth and their quality of life is often severely affected. Recently, research into the pathomechanisms of these severe congenital ichthyoses have advanced dramatically and led to the identification of several causative genes and molecules underlying the genetic defects. To date, seven loci have been identified that are associated with ARCI and, among them, five causative genes and molecules have been detected. The five genes are transglutaminase 1 gene (TGM1), ABCA12, two lipoxygenase genes, ALOXE3 and ALOX12B and ichthyin. One of these components, ABCA12, has recently been shown to be a keratinocyte lipid transporter associated with lipid transport in lamellar granules and loss of ABCA12 function leads to a defective lipid barrier in the stratum corneum, resulting in the HI phenotype. Transglutaminse 1 deficiency was reported to cause a malformed cornified cell envelope leading to a defect in the intercellular lipid layers in the stratum corneum and defective stratum corneum barrier function resulting in an ichthyosis phenotype. Thus, defective intercellular lipid layers are major findings in autosomal recessive congenital ichthyoses. Information concerning ARCI genetic defects and disease pathomechanisms are beneficial for providing better treatments and genetic counseling including prenatal diagnosis for families affect by ichthyoses.     

Management of the ichthyoses

The ichthyoses are a heterogeneous group of inherited scaling skin disorders that can also affect other organs. Management should be directed at both the skin and other sites. Skin therapy is not specific at this time, although new products may offer more directed therapy in the future. Moisturizers and keratolytics are the mainstay of topical therapy. Calcipotriene, retinoids, and for select types, anti-inflammatories such as topical steroids and calcineurin inhibitors have also been used. Systemic therapy is limited to the retinoids. Superinfection of the skin should be anticipated and treated. Pruritus can be disabling. Failure to sweat normally may result in heat intolerance. Eye care should seek to prevent corneal changes resulting from ectropion and more specific changes associated with specific disorders. Haring can be impaired by the accumulation of material in the external auditory canal. Severely affected children may require caloric supplementation to avoid growth retardation. Affected individuals and their family should be counseled about the long term outlook and the genetic nature of their disorder, and informed of FIRST, the Foundation for Ichthyosis and Related Skin Types, the lay foundation that offers support and information.     

Retinoic acid metabolism blocking agents (RAMBAs): a new paradigm in the treatment of hyperkeratotic disorders

Synthetic vitamin A derivatives, retinoids,have long been the mainstay of treatment for several disorders of keratinization, notably the ichthyoses and severe acne. Some forms of psoriasis also respond well. Their considerable power comes at a price.They have dose‐limiting side effects and can be highly teratogenic, limiting their use in women of childbearing age.Thus, retinoids are used less often than their potential would warrant. However, the recent development of compounds that block the catabolism of endogenous vitamin A, called Retinioic Acid Metabolism Blocking Agents or RAMBAs, offers new possibilities. With these drugs, retinoid effects with less side effects and a reduction of the post‐treatment teratogenicity period due to their favourable pharmacokinetic profile might be expected. In this review, we discuss how retinoids work, how they are metabolized and how RAMBAs influence this process.We also review the presently available data from clinical trials with RAMBAs.     

Hereditary palmoplantar keratodermas. Part II: syndromic palmoplantar keratodermas – Diagnostic algorithm and principles of therapy

Hereditary palmoplantar keratodermas (PPKs) comprise a large and heterogeneous group of disorders characterized by persistent thickening of the epidermis at palmar and plantar surfaces. Clinical and genetic features of isolated and complex PPKs have been reviewed in part I of this 2‐part review. Here we focus on clinical and molecular classification of syndromic PPKs which are recognized by additional extracutaneous manifestations, in particular deafness, specific mucosal lesions, cardiomyopathy, inborn errors of metabolism, involvement of internal organs or disorders of sexual development. Other genetic diseases, which may show palmoplantar involvement, such as selected subtypes of hereditary epidermolysis bullosa, various hereditary ichthyoses and other keratinization disorders, several ectodermal dysplasias and some multisystem genetic disorders, are also briefly summarized. PPK diagnosis is based on inheritance pattern, age at onset, morphology, distribution and severity of hyperkeratosis, pattern of additional dermatological and systemic manifestations and laboratory findings. Molecular analysis is at present the gold standard to confirm the diagnosis in PPK forms due to mutations in known causative genes. No specific and curative therapy is currently available for PPKs which highly impair patients’ quality of life. Topical treatments are symptomatic and offer only temporary relief. Among systemic treatments, retinoids improve disease symptoms in the majority of patients.     

Klinik und ?tiologie der Ichthyosen

Ichthyoses comprise a heterogeneous group of Mendelian disorders of cornification (MEDOC) affecting the entire skin and characterized by hyperkeratosis and/or scaling. The genetic basis of almost all ichthyosis forms has been elucidated. In 2009, the worldwide first Ichthyosis Consensus Classification was approved. Its nosology is based on the clinical presentation and reflects recent pathogenic aspects. It distinguishes basically between non-syndromic and syndromic ichthyoses. The term ARCI/autosomal recessive congenital ichthyosis represents the umbrella for harlequin ichthyosis, lamellar ichthyosis and congenital ichthyosiform erythroderma. Ichthyoses due to keratin mutations are referred to as KPI/keratinopathic ichthyosis and include epidermolytic ichthyosis (EI) and superficial epidermolytic ichthyosis (SEI). In Germany the Network for Ichthyoses and Related Keratinization Disorders (NIRK) and the patient organization Selbsthilfe Ichthyose e.V. provide contact points for diagnostic and therapeutic questions.     

Care of the newborn with ichthyosis

Mendelian disorders of cornification (ichthyosis; MeDOC) often present in the neonatal period with little warning to providers or parents. This report reviews the majority of ichthyoses with congenital findings. The neonatal presentation of many MeDOC often differs from the later phenotype because of the changes in the skin that occur with transition from an intrauterine to extrauterine environment. While differentiation of ichthyosis subtypes in the neonatal period is difficult, there are certain phenotypic groups within which these neonates fall, recognition of which can guide initial work up and treatment. For this report, these are categorized as: exuberant vernix; collodion baby/harlequin ichthyosis (HI); ichthyosiform erythroderma; blistering; and normal skin/xerosis phenotypes.     

Complications of ichthyosis beyond the skin

Although ichthyoses are noted for their skin features, like many dermatologic conditions, patients are often impacted in ways beyond the skin. Much has been described in recent years regarding quality of life and skin disorders. This is certainly the case for ichthyosis. For neonates or others with diffuse involvement of their skin, nutritional needs are often exceeding normal requirements. These can often result in growth abnormalities. Lastly, with specific subtypes of ichthyosis, compromise of tissues around the eyes and ears can be of concern to some patients. Certainly, some forms of ichthyosis are routinely complicated by such findings. It is important for practitioners caring for individuals with ichthyosis to have these issues in mind.     

Management of congenital ichthyoses: European guidelines of care,part one

These guidelines for the management of congenital ichthyoses have been developed by a multidisciplinary group of European experts following a systematic review of the current literature, an expert conference held in Toulouse in 2016 and a consensus on the discussions. They summarize evidence and expert-based recommendations and are intended to help clinicians with the management of these rare and often complex diseases. These guidelines comprise two sections. This is part one, covering topical therapies, systemic therapies, psychosocial management, communicating the diagnosis and genetic counselling.     

Molecular genetic assays for inherited epidermolysis bullosa

Epidermolysis bullosa (EB) is a heterogeneous group of genetic disorders, characterized by blistering of skin and mucosal membranes under normal mechanical stress conditions. The clinical phenotype ranges from mild localized to severe generalized disease with secondary extracutaneous symptoms and premature death. The lives of the patients and their families are marked by this disorder, causing severe physical, psychologic, and material burdens. The four major EB types are classified by the level of skin blistering, but more than 30 subtypes can be distinguished, according to clinical and molecular genetic criteria. So far, mutations in 14 genes are known to cause different EB subtypes. The diagnosis of the EB subtype is essential for the prognosis, genetic counseling, and prenatal diagnosis. Because the symptoms are often overlapping or not specific, the diagnosis of the EB type is usually not possible by clinical criteria or routine histologic examination. Immunofluorescence analysis of skin sections with antibodies to proteins of the basement membrane zone is the first diagnostic step to indicate the level of skin split and the missing protein. Mutation analysis indicates the precise cause of the disease, the affected gene, and the inheritance pattern.     

Haut und Zähne

Skin and teeth not only share several characteristics in their development but also have a similar ontogenetic origin from the ectoderm. Thus, numerous congenital diseases, such as genetic, infectious, inflammatory, and immune disorders affect both skin and teeth. Particularly skin diseases are often identified by the synopsis of systemic symptoms. The understanding and appreciation of dental abnormalities guides dermatologists in the diagnosis and identification of syndromes as well as in finding an optimal therapy.     

角蛋白鱼鳞病研究进展

角蛋白鱼鳞病即由角蛋白基因缺陷所致的鱼鳞病,其致病基因主要是角蛋白1、角蛋白2和角蛋白10基因。本文详细介绍了先天性大疱性鱼鳞病样红皮病和Siemens大疱性鱼鳞病基因突变的遗传学特点和基因型与临床表型的关系,以及另外四种少见角蛋白鱼鳞病的临床特征及基因遗传学特点。     

Hereditäre Stoffwechselerkrankungen mit kutaner Manifestation

Over the last years, the genetic basis of several monogenic inherited metabolic diseases has been elucidated. Interestingly, some of these disorders manifest with characteristic cutaneous symptoms that are often crucial for diagnosis. In most cases, however, besides the skin other organs are affected. Therefore, an interdisciplinary supervision of these patients is highly important. In this review we will discuss diseases that constitute a challenge not only for dermatologists but also for physicians from other specialties. A particular emphasis is put on genetic and clinical features of these disorders as well as current therapeutic concepts.     

A child with hypohidrotic ectodermal dysplasia with features of a collodion membrane

Collodion membrane is a presenting phenotype common to several disorders, predominantly congenital ichthyoses. Seventy percent of infants born with hypohidrotic (anhidrotic) ectodermal dysplasia are noted by their parents to have significant scaling and peeling. Although dry skin is a frequently reported sign in children with hypohidrotic ectodermal dysplasia, only one French study has reported a true collodion membrane at birth. We suspect that scaling with features of collodion membrane is more common in infants than is reflected in the literature, and we describe another such infant, later diagnosed with hypohidrotic ectodermal dysplasia.