Regional difference in expression of characteristic abnormality of harlequin ichthyosis in affected fetuses

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.

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.

Epidemiology, medical genetics, diagnosis and treatment of harlequin ichthyosis in Japan

Ichthyoses are a group of disorders marked by whitish, brown or dark-brown scales on the skin of almost the whole body. Harlequin ichthyosis (HI) is the most severe form. Neonatal death from HI was once common. Due to intensive neonatal care and, probably, to the early introduction of oral retinoids, HI outcome has improved. For definitive diagnosis and the exclusion of other disorders, such as lamellar ichthyosis, which also shows a collodion baby phenotype, it is helpful to refer to electron microscopy of abnormal or absent lamellar granules and a heavy accumulation of lipid droplets in the keratinocytes. ATP-binding cassette transporter A12 (ABCA12) is known as the causative gene of HI. Severe ABCA12 deficiency results in malformation of intercellular lipid layers in the cornified layers and leads to epidermal lipid barrier disruption. In HI patients, at least one mutation on each allele must be a truncation or deletion mutation to cause serious loss of ABCA12 function. Identification of the gene underlying HI has enabled DNA-based prenatal diagnosis for HI at the earlier stages of pregnancy with low risk. There are no curative treatments for HI. Abca12-deficient mice were created as a model of HI. Treatment of the model mice with retinoid or steroid has not been successful.

Harlequin Infant Born to a Varicella Infected Mother: A Case Report

Harlequin ichthyosis is a rare, severe form of congenital ichthyosis characterised by distinct physical appearance of the infant. It has occurrence of 1 in 1 million births and over 100 cases have been reported so far. It is caused by mutation in ABCA12 gene involved in lipid transport leading to profound thickening of stratum corneum. The mainstay of management relies on supportive care & administration of retinoid derivatives. Outcome is usually fatal and most of the babies die during neonatal period. In this article, we report a case of harlequin baby born of non-consanguineous marriage with history of chicken pox in the mother during first trimester of pregnancy.

The roles of ABCA12 in epidermal lipid barrier formation and keratinocyte differentiation

ATP-binding cassette (ABC) transporters form a large superfamily of transporters that bind and hydrolyze ATP to transport various molecules across limiting membranes or into vesicles. The ABCA subfamily members are thought to transport lipid materials. ABCA12 is a keratinocyte transmembrane lipid transporter protein associated with the transport of lipids via lamellar granules. ABCA12 is considered to transport lipids including ceramides to form extracellular lipid layers in the stratum corneum of the epidermis, which is essential for skin barrier function. ABCA12 mutations are known to underlie the three major types of autosomal recessive congenital ichthyoses: harlequin ichthyosis, lamellar ichthyosis and congenital ichthyosiform erythroderma. ABCA12 mutations result in defective lipid transport via lamellar granules in the keratinocytes, leading to ichthyosis phenotypes from malformation of the stratum corneum lipid barrier. Studies on ABCA12-deficient bioengineered models have revealed that lipid transport by ABCA12 is required for keratinocyte differentiation and epidermal morphogenesis. Defective lipid transport due to loss of ABCA12 function leads to the accumulation of intracellular lipids, including glucosylceramides and gangliosides, in the epidermal keratinocytes. The accumulation of gangliosides seems to result in the apoptosis of Abca12(-/-) keratinocytes. It was reported that AKT activation occurs in Abca12(-/-) granular-layer keratinocytes, which suggests that AKT activation serves to prevent the cell death of Abca12(-/-) keratinocytes. This article is part of a Special Issue entitled The Important Role of Lipids in the Epidermis and their Role in the Formation and Maintenance of the Cutaneous Barrier. Guest Editors: Kenneth R. Feingold and Peter Elias.

The roles of ABCA12 in keratinocyte differentiation and lipid barrier formation in the epidermis

ABCA12 is a member of the large superfamily of ATP-binding cassette (ABC) transporters, which bind and hydrolyze ATP to transport various molecules across limiting membranes or into vesicles. The ABCA subfamily members are thought to be lipid transporters. ABCA12 is a keratinocyte transmembrane lipid transporter protein associated with the transport of lipids in lamellar granules to the apical surface of granular layer keratinocytes. Extracellular lipids, including ceramide, are thought to be essential for skin barrier function. ABCA12 mutations are known to underlie the three main types of autosomal recessive congenital ichthyoses: harlequin ichthyosis, lamellar ichthyosis and congenital ichthyosiform erythroderma. ABCA12 mutations lead to defective lipid transport via lamellar granules in the keratinocytes, resulting in malformation of the epidermal lipid barrier and ichthyosis phenotypes. Studies of ABCA12-deficient model mice indicate that lipid transport by ABCA12 is also indispensable for intact differentiation of keratinocytes.

Premature terminal differentiation and a reduction in specific proteases associated with loss of ABCA12 in Harlequin ichthyosis

One of the primary functions of skin is to form a defensive barrier against external infections and water loss. Disrupted barrier function underlies the most severe and often lethal form of recessive congenital ichthyosis, harlequin ichthyosis (HI). HI is associated with mutations in the gene that encodes the ABC transporter protein, ABCA12. We have investigated the morphological and biochemical alterations associated with abnormal epidermal differentiation and barrier formation in HI epidermis. An in vitro model of HI skin using human keratinocytes retrovirally transduced with shRNA targeting ABCA12 in a three-dimensional, organotypic co-culture (OTCC) system has also been developed. A robust reduction in ABCA12 expression had a dramatic effect on keratinocyte differentiation and morphology comparable with that observed in HI skin, including a thicker epidermis and abnormal lipid content with a reduction in nonpolar lipids. As seen in HI epidermis, proteins that are normally expressed in late differentiation were highly dysregulated in the ABCA12-ablated OTCC system. These proteins were expressed in the stratum basale and also in the stratum spinosum, indicative of a premature terminal differentiation phenotype. Expression of the proteases kallikrein 5 and cathepsin D was dramatically reduced in both HI epidermis and the OTCC model. These data suggest that ABCA12 is a key molecule in regulating keratinocyte differentiation and transporting specific proteases associated with desquamation.

Ichthyosis congenita, harlequin fetus type: a case report

Ichthyosis is a very heterogeneous family of skin disorders with harlequin ichthyosis being the most severe genetic form. It is a rare autosomal recessive condition, characterized by dry, severely thickened skin with large plates of hyperkeratotic scale, separated by deep fissures. Infants are very susceptible to metabolic abnormalities and infections. They usually do not survive for very long, but several long term survivals have been noted. The vast majority of affected individuals are homozygous for mutations in the ABCA12 gene, which cause a deficiency of the epidermal lipid transporter, resulting in hyperkeratosis and abnormal barrier function. We report a case of a newborn with harlequin ichthyosis, born to unrelated parents, who had a favorable evolution with topical treatment and intensive care.

Expression of the keratinocyte lipid transporter ABCA12 in developing and reconstituted human epidermis

Serious defects in the epidermal keratinocyte lipid transporter ABCA12 are known to result in a deficient skin lipid barrier, leading to harlequin ichthyosis (HI). HI is the most severe inherited keratinizing disorder and is frequently fatal in the perinatal period. To clarify the role of ABCA12, ABCA12 expression was studied in developing human skin and HI lesions artificially reconstituted in immunodeficient mice. By immunofluorescent study, ABCA12 was expressed in the periderm of the early stage two-layered human fetal epidermis. After formation of a three-layered epidermis, ABCA12 staining was seen throughout the entire epidermis. ABCA12 mRNA expression significantly increased during human skin development and reached 62% of the expression in normal adult skin, whereas the expression rate of transglutaminase 1, loricrin, and kallikrein 7 remained low. We transplanted keratinocytes from patients with HI and succeeded in reconstituting HI skin lesions in immunodeficient mice. The reconstituted lesions showed similar changes to those of patients with HI. Our findings demonstrate that ABCA12 is highly expressed in fetal skin and suggest that ABCA12 may play an essential role under both the wet and dry conditions, including the dramatic turning point from a wet environment of the amniotic fluid to a dry environment after birth.

DNA-Based Prenatal Diagnosis of Harlequin Ichthyosis and Characterization of ABCA12 Mutation Consequences

Until the identification of ABCA12 as the causative gene, prenatal diagnosis (PD) for harlequin ichthyosis (HI) had been performed by electron microscopic observation of fetal skin biopsy samples. We report the first case of HI DNA-based PD. Direct sequence analysis of ABCA12 revealed that the deceased proband was a compound heterozygote for two novel mutations. The maternal nonsense mutation p.Ser1249Term likely leads to nonsense-mediated messenger RNA decay. The paternal mutation c.7436G>A affects the last codon of exon 50 and was expected to be a splice site mutation. For their third pregnancy, the parents requested PD. Direct sequence analysis of fetal genomic DNA from amniotic fluid cells at 17 weeks gestation revealed the fetus was a compound heterozygote for both mutations. The parents requested the pregnancy to be terminated. Analysis of ABCA12 transcripts of cultured keratinocytes from the abortus showed the presence of six abnormally spliced products from the allele carrying the splice site mutation. Four of them lead to premature termination codons whereas the two others produced shortened proteins missing 21 and 31 amino acids from the second ATP-binding cassette. This report provides evidence for residual ABCA12 expression in HI, and demonstrates the efficiency of early DNA-based PD of 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.

A review of harlequin ichthyosis

Harlequin ichthyosis is an extremely rare and historically lethal congenital disorder of the skin caused by abnormal keratinization. This article reviews the embryology and currently understood pathophysiology of the disease, as well as current methods used to diagnose and treat these infants. There are serious implications for the family to consider: the high risk that their newborn will die soon, as well as future family planning issues.

Mutations in ABCA12 underlie the severe congenital skin disease harlequin ichthyosis

Harlequin ichthyosis (HI) is the most severe and frequently lethal form of recessive congenital ichthyosis. Although defects in lipid transport, protein phosphatase activity, and differentiation have been described, the genetic basis underlying the clinical and cellular phenotypes of HI has yet to be determined. By use of single-nucleotide-polymorphism chip technology and homozygosity mapping, a common region of homozygosity was observed in five patients with HI in the chromosomal region 2q35. Sequencing of the ABCA12 gene, which maps within the minimal region defined by homozygosity mapping, revealed disease-associated mutations, including large intragenic deletions and frameshift deletions in 11 of the 12 screened individuals with HI. Since HI epidermis displays abnormal lamellar granule formation, ABCA12 may play a critical role in the formation of lamellar granules and the discharge of lipids into the intercellular spaces, which would explain the epidermal barrier defect seen in this disorder. This finding paves the way for early prenatal diagnosis. In addition, functional studies of ABCA12 will lead to a better understanding of epidermal differentiation and barrier formation.

The human cystatin M/E gene (CST6): exclusion candidate gene for harlequin ichthyosis

Cystatin M/E is a recently discovered cysteine proteinase inhibitor whose expression is largely confined to cutaneous epithelia. In human skin it is expressed in sweat glands, hair follicles, and stratum granulosum of the epidermis where it presumably acts as a substrate for transglutaminase. Very recently we reported that a null mutation in the mouse cystatin M/E gene (Cst6) causes the murine ichq phenotype, which is characterized by abnormalities in cornification and desquamation, demonstrating an essential role for cystatin M/E in the final stages of epidermal differentiation. We here obtained the complete sequence of the human cystatin M/E gene (CST6), which provides a tool to investigate CST6 as a candidate gene in skin diseases characterized by abnormal cornification. The involvement of CST6 in harlequin ichthyosis in humans was evaluated by sequencing the entire coding region and intron-exon boundaries for mutations in 11 sporadic harlequin ichthyosis patients. No CST6 mutations were detected in this group, which comprised type 1 and type 2 harlequin ichthyosis patients. Disturbed transcription/translation due to mutations in regulatory and noncoding regions of cystatin M/E was unlikely because cystatin M/E protein expression was observed in all patients examined, as assessed by immunohistochemistry. Although our results indicate that CST6 is not a major gene contributing to type 1 and 2 harlequin ichthyosis, these data may facilitate further analysis of the role of cystatin M/E in normal human skin and other genetic disorders of cornification.

Harlequin ichthyosis in two greater kudu (Tragelaphus strepsiceros)

Two greater kudu calves (Tragelaphus strepsiceros) born 7 years apart were found with fissures and thickened, scaly, cutaneous plates covering over 80% of their bodies. One was dead at presentation, and the other was euthanized shortly after birth. Both animals shared a common sire. On necropsy, chemosis, ectropion, eclabium, and bilateral valgus deformities of the tarsal joints were observed in one calf, presumed to be secondary to the plates restricting normal fetal development. The principal microscopic lesion was severe lamellar orthokeratosis, with focal mild parakeratosis. Ultrastructural epidermal lesions included the absence of normal lamellar granules, large dilated endoplasmic reticulum, and abnormal retention of organelles and vesicles. Gross, histopathologic, and electron microscopic findings in both kudu calves were consistent with those of harlequin ichthyosis, a rare dermatosis of humans believed to have an autosomal recessive inheritance pattern. The underlying genetic and molecular abnormality and heritability of this condition in this greater kudu herd were not determined.

Harlequin fetus: a case report

We report a case of harlequin fetus. This very rare cutaneous malformation is a severe form of congenital ichthyosis. This disorder is due to an inborn error of epidermal keratinization. Malformations of ears, nose, and hypoplasia of fingers or nails are seen. This affection is most often lethal.

Prenatal diagnosis as a test for genodermatoses: its past, present and future

The prenatal diagnosis (PND) of severe hereditary skin diseases started in the early 1980s using fetal skin biopsy techniques based on ultrastructural and immunohistochemical abnormalities of the fetal skin. Recent success in identifying responsible genes and demonstrating mutations in such genes has set the stage for DNA-based PND in the 1990s. Common examples of skin conditions which can be prenatally diagnosed include epidermolysis bullosa, oculocutaneous albinism and Harlequin ichthyosis in which the severity of the clinical phenotype appears to justify PND in families at risk. More recently, preimplantation diagnoses of inherited diseases have become possible using in vitro fertilization techniques. The diagnosis consists of a blastomere biopsy of the six to ten-cell embryo and a DNA analysis of single blastomeres. Disease-free embryos are selected for transfer to the uterus, thereby avoiding the need for termination of a fetus found to be affected by conventional PND. Furthermore, carrying out a PND using a single fetal cell from the maternal blood, such as nucleated erythrocytes, has become technically feasible. Although there are many questions that remain unanswered, the outlook for further development of noninvasive PND in the future appears optimistic.