Clouston Syndrome Can Mimic Pachyonychia Congenita

A novel variant in the GJB6 gene in a large Chinese family with a unique phenotype of Clouston syndrome

Clouston syndrome (OMIM #129500), also known as hidrotic ectodermal dysplasia type 2, is a rare autosomal dominant skin disorder. To date, four mutations in the GJB6 gene, G11R, V37E, A88V, and D50N, have been confirmed to cause this condition. In previous studies, the focus has been mainly on gene sequencing, and there has been a lack of research on clinical manifestations and pathogenesis. To confirm the diagnosis of this pedigree at the molecular level and summarize and analyse the clinical phenotype of patients and to provide a basis for further study of the pathogenesis of the disease, we performed whole-exome and Sanger sequencing on a large Chinese Clouston syndrome pedigree. Detailed clinical examination included histopathology, hair microscopy, and scanning electron microscopy. We found a novel heterozygous missense variant (c.134G>C:p.G45A) for Clouston syndrome. We identified a new clinical phenotype involving all nail needling pain in all patients and found a special honeycomb hole structure in the patients' hair under scanning electron microscopy. Our data reveal that a novel variant (c.134G>C:p.G45A) plays a likely pathogenic role in this pedigree and highlight that genetic testing is necessary for the diagnosis of Clouston syndrome.

Immune system disturbances in Clouston syndrome

BACKGROUND

Clouston syndrome belongs to the family of ectodermal dysplasias. So far, a defective immune response has not been reported in Clouston syndrome. We report, for the first time, immunological particularities of a large multigenerational Polish family with Clouston syndrome.

METHODS

Five members of the same family with Clouston syndrome, aged 6-76 years, and 20 healthy volunteers, aged 19-73 years, were enrolled in the study. In all participants, the ability of neutrophils to phagocytize opsonized Escherichia coli was assessed. Granulocyte oxidative burst was determined quantitatively, and an isolation of peripheral blood mononuclear cells and the detection of lymphocyte subsets were performed. All patients with Clouston syndrome underwent microscopic assessment of hair shafts, x-rays of the skull and hand bones, extra- and intraoral examination, and panoramic x-rays.

RESULTS

Compared to the controls, all patients with Clouston syndrome presented with significantly reduced phagocytic activities of granulocytes and monocytes (P < 0.05). The percentages of granulocytes and monocytes being positive for oxidative burst were also significantly reduced in all patients with Clouston syndrome (P < 0.05). No disturbances in the percentages and absolute counts of T CD3+, T CD3+/CD4+, T CD3+/CD8+, natural killer, and B CD19+ cells were found.

CONCLUSION

Although this study expands knowledge about Clouston syndrome, it also raises many questions. The results provide evidence of significantly reduced phagocytic activity and oxidative bursts of cells playing crucial roles in a nonspecific immune response. Further studies are required to understand the underlying mechanism of the hereby described abnormalities.

Connexins and pannexins in the integumentary system: the skin and appendages

The integumentary system comprises the skin and its appendages, which includes hair, nails, feathers, sebaceous and eccrine glands. In this review, we focus on the expression profile of connexins and pannexins throughout the integumentary system in mammals, birds and fish. We provide a picture of the complexity of the connexin/pannexin network illustrating functional importance of these proteins in maintaining the integrity of the epidermal barrier. The differential regulation and expression of connexins and pannexins during skin renewal, together with a number of epidermal, hair and nail abnormalities associated with mutations in connexins, emphasize that the correct balance of connexin and pannexin expression is critical for maintenance of the skin and its appendages with both channel and non-channel functions playing profound roles. Changes in connexin expression during both hair and feather regeneration provide suggestions of specialized communication compartments. Finally, we discuss the potential use of zebrafish as a model for connexin skin biology, where evidence mounts that differential connexin expression is involved in skin patterning and pigmentation.

Connexins and skin disease: insights into the role of beta connexins in skin homeostasis

Cell-to-cell communication triggered by connexin channels plays a central role in maintaining epidermal homeostasis. Here, we discuss the role of the beta connexin subgroup, where site-specific mutations in at least 4 of these proteins lead to distinctive non-inflammatory and inflammatory hyperproliferative epidermal disorders. Recent advances in the molecular pathways evoked and correlation with clinical outcome are discussed. The latest data provide increasing evidence that connexins in the epidermis are sensors to environmental stress and that targeting aberrant hemichannel activity holds significant therapeutic potential for inflammatory skin disorders.

The molecular genetic analysis of the expanding pachyonychia congenita case collection

BACKGROUND

Pachyonychia congenita (PC) is a rare autosomal dominant keratinizing disorder characterized by severe, painful, palmoplantar keratoderma and nail dystrophy, often accompanied by oral leucokeratosis, cysts and follicular keratosis. It is caused by mutations in one of five keratin genes: KRT6A, KRT6B, KRT6C, KRT16 or KRT17.

OBJECTIVES

To identify mutations in 84 new families with a clinical diagnosis of PC, recruited by the International Pachyonychia Congenita Research Registry during the last few years.

METHODS

Genomic DNA isolated from saliva or peripheral blood leucocytes was amplified using primers specific for the PC-associated keratin genes and polymerase chain reaction products were directly sequenced.

RESULTS

Mutations were identified in 84 families in the PC-associated keratin genes, comprising 46 distinct keratin mutations. Fourteen were previously unreported mutations, bringing the total number of different keratin mutations associated with PC to 105.

CONCLUSIONS

By identifying mutations in KRT6A, KRT6B, KRT6C, KRT16 or KRT17, this study has confirmed, at the molecular level, the clinical diagnosis of PC in these families.

Ectodermal dysplasias: a clinical and molecular review

The ectodermal dysplasias are a large group of hereditary disorders characterized by alterations of structures of ectodermal origin. Although some syndromes can have specific features, many of them share common clinical characteristics. Two main groups of ectodermal dysplasias can be distinguished. One group is characterized by aplasia or hypoplasia of ectodermal tissues, which fail to develop and differentiate because of a lack of reciprocal signaling between ectoderm and mesoderm, the other has palmoplantar keratoderma as its most striking feature, with additional manifestations when other highly specialized epithelia are also involved. In recent decades, the genes responsible for at least 30 different types of ectodermal dysplasia have been identified, throwing light on the pathogenic mechanisms involved and their correlation with clinical findings.

Double trouble: homozygous dominant mutations and hair loss in pachyonychia congenita

In this issue, Wilson et al. report the first case of homozygous dominant negative mutations in KRT17 in pachyonychia congenita (PC). Homozygous dominant negative mutations are a rare occurrence in keratin disorders and this is a first report in PC. These mutations cause a distinct sub-phenotype of PC that is more severe in the offspring of affected parents and has associated alopecia.

Pachyonychia congenita with laryngeal obstruction

Pachyonychia congenita is a rare genodermatosis that can affect the larynx. Laryngeal obstruction is very unusual with only a few cases reported. A 2-year-old girl presented with typical clinical features of pachyonychia congenita shortly after birth. At age 9 months, following an upper respiratory infection, she developed stridor and hoarseness and was found to have severe laryngeal obstruction, which was felt to be secondary to pachyonychia congenita based on direct laryngoscopy and laryngeal biopsy. Leukokeratosis of her larynx was treated with CO(2) laser on three occasions, with improvement in her respiratory distress after each treatment. This report is the first case of pachyonychia congenita with laryngeal obstruction in which the gene mutation has been established (a deletional mutation in K6a), confirming that laryngeal obstruction can occur in PC-1.

Genetic testing in ectodermal dysplasia: availability, clinical utility, and the nuts and bolts of ordering a genetic test

"Ectodermal Dysplasia syndromes" comprise a diverse group of heritable conditions characterized by congenital anomalies of one or more ectodermal structures and their appendages: hair, teeth, nails, and sweat glands. Genetic testing is available for many types of ectodermal dysplasia (ED) through clinical and/or research laboratories. We address the distinctions between genetic testing as performed on a clinical versus research basis, and summarize the clinical aspects, testing methodology, and sensitivity for those ED syndromes for which testing is available in a clinical laboratory. Lastly, we leave the laboratory for the clinical setting to discuss the utility of genetic testing for patients and their families, and summarize the practical issues involved in ordering a genetic test.

Genetic diseases of junctions

Tight junctions, gap junctions, adherens junctions, and desmosomes represent intricate structural intercellular channels and bridges that are present in several tissues, including epidermis. Clues to the important function of these units in epithelial cell biology have been gleaned from a variety of studies including naturally occurring and engineered mutations, animal models and other in vitro experiments. In this review, we focus on mutations that have been detected in human diseases. These observations provide intriguing insight into the biological complexities of cell-cell contact and intercellular communication as well as demonstrating the spectrum of inherited human diseases that are associated with mutations in genes encoding the component proteins. Over the last decade or so, human gene mutations have been reported in four tight junction proteins (claudin 1, 14, 16, and zona occludens 2), nine gap junction proteins (connexin 26, 30, 30.3, 31, 32, 40, 43, 46, and 50), one adherens junction protein (P-cadherin) and eight components of desmosomes (plakophilin (PKP) 1 and 2, desmoplakin, plakoglobin--which is also present in adherens junctions, desmoglein (DSG) 1, 2, 4, and corneodesmosin). These discoveries have often highlighted novel or unusual phenotypes, including abnormal skin barrier function, alterations in epidermal differentiation, and developmental anomalies of various ectodermal appendages, especially hair, as well as a range of extracutaneous pathologies. However, this review focuses mainly on inherited disorders of junctions that have an abnormal skin phenotype.

Treatment of pachyonychia congenita with plantar injections of botulinum toxin

Pachyonychia congenita (PC) is a rare genodermatosis which may be associated with painful, focal hyperkeratosis on the soles. Plantar sweating at high ambient temperatures increases the blistering of the callosities. We report three patients with PC who had great problems in walking, especially during summer time. They were treated with intracutaneous plantar injections of botulinum toxin type A (Dysport, 100 U mL(-1); Ipsen, Slough, U.K.) after prior intravenous regional anaesthesia of the foot with a low tourniquet and 25 mL prilocaine (5 mg mL(-1)). Within a week all three patients experienced dryness and a remarkable relief of pain from plantar pressure sites. The effect duration was 6 weeks to 6 months. Repeated injections over a 2-year period confirmed the good results, with no side-effects or tachyphylaxis noted.

The genetic basis of pachyonychia congenita

In 1994, the molecular basis of pachyonychia congenita (PC) was elucidated. Four keratin genes are associated with the major subtypes of PC: K6a or K16 defects cause PC-1; and mutations in K6b or K17 cause PC-2. Mutations in keratins, the epithelial-specific intermediate filament proteins, result in aberrant cytoskeletal networks which present clinically as a variety of epithelial fragility phenotypes. To date, mutations in 20 keratin genes are associated with human disorders. Here, we review the genetic basis of PC and report 30 new PC mutations. Of these, 25 mutations were found in PC-1 families and five mutations were identified in PC-2 kindreds. All mutations identified were heterozygous amino acid substitutions or small in-frame deletion mutations with the exception of an unusual mutation in a sporadic case of PC-1. The latter carried a 117 bp duplication resulting in a 39 amino acid insertion in the 2B domain of K6a. Also of note was mutation L388P in K17, which is the first genetic defect identified in the helix termination motif of this protein. Understanding the genetic basis of these disorders allows better counseling for patients and paves the way for therapy development.

Insights into genotype-phenotype correlation in pachyonychia congenita from the human intermediate filament mutation database

Keratins are the intermediate filament proteins specifically expressed by epithelial cells. The Human Genome Project has uncovered a total of 54 functional keratin genes that are differentially expressed in specific epithelial structures of the body, many of which involve the epidermis and its appendages. Pachyonychia congenita (PC) is a group of autosomal dominant genodermatoses affecting the nails, thick skin and other ectodermal structures, according to specific sub-type. The major clinical variants of the disorder (PC-1 and PC-2) are known to be caused by dominant-negative mutations in one of four differentiation-specific keratins: K6a, K6b, K16, and K17. A total of 20 human keratin genes are currently linked to single-gene disorders or are predisposing factors in complex traits. In addition, a further six intermediate filament genes have been linked to other non-epithelial genetic disorders. We have established a comprehensive mutation database that catalogs all published independent occurrences of intermediate filament mutations (http://www.interfil.org), with details of phenotypes, published papers, patient support groups and other information. Here, we review the genotype-phenotype trends emerging from the spectrum of mutations in these genes and apply these correlations to make predictions about PC phenotypes based on the site of mutation and keratin pair involved.

Gap junction diseases of the skin

Gap junctions are intercellular channels that allow the passage of water, ions, and small molecules. They are involved in quick, short-range messaging between cells and are found in skin, nervous tissue, heart, and muscle. An increasing number of hereditary skin disorders appear to be caused by mutations in one of the genes coding for the constituent proteins of gap junctions, known as connexins. In this review, the currently known connexin disorders that feature skin abnormalities are described: keratitis-ichthyosis deafness syndrome, erythrokeratoderma variabilis, Vohwinkel's syndrome, and a novel disorder called hypotrichosis-deafness syndrome. What is known about the pathogenesis of these disorders is discussed and related to gap junction physiology.

Connexin disorders of the skin

Over the past decade, the molecular basis of most disorders of cornification has been unveiled. Among these, a distinct group has emerged because of primary defects in cell-cell communication due to faulty gap junction proteins also known as connexins. This review aims to delineate the cutaneous connexin disorders and to highlight intriguing genotype-phenotype correlations and emanating clinical implications.

Genetic heterogeneity of KID syndrome: identification of a Cx30 gene (GJB6) mutation in a patient with KID syndrome and congenital atrichia

Connexins are integral membrane proteins forming aqueous gap junction channels that allow the diffusional exchange of ions and small metabolites between cells, thus coordinating metabolic activities in multicellular tissues. Dominant mutations in the Cx26 gene GJB2 have been shown to cause keratitis-ichthyosis-deafness (KID) syndrome, palmoplantar keratoderma associated with hearing loss, and Vohwinkel syndrome. Missense mutations in the closely related Cx30 gene GJB6 underlie Clouston syndrome (autosomal dominant hidrotic ectodermal dysplasia). We report a 6-y-old boy with phenotypic characteristics of KID syndrome as well as atrichia. In contrast to other KID syndrome patients, molecular analysis of the connexin gene GJB2 did not disclose a pathogenic mutation, although the patient was homozygous for a common polymorphism (V27I) in the coding sequence of Cx26. Nevertheless, screening of GJB6 revealed a heterozygous missense mutation (V37E) predicted to alter sequence and charge of the first transmembrane helix of Cx30, which was previously implicated in Clouston syndrome (Smith et al, 2002). The presence of a pathogenic Cx30 mutation and the lack of a pathologic molecular change in Cx26 in this patient, whose clinical features predominantly resemble KID syndrome, suggest genetic heterogeneity of KID syndrome and underscore that mutations in Cx30, similar to those in Cx26 or Cx31, can cause different phenotypes. Based on our results, connexin gene mutations should be considered in patients presenting with congenital sensorineural hearing loss and disorders of cornification, and screening of several connexin genes with known cutaneous phenotype, such as those for Cx26, Cx30, Cx30.3, and Cx31, may be required.

Psoriasis, PUVA, and skin cancer--molecular epidemiology: the curious question of T-->A transversions

Photochemotherapy with 8-methoxypsoralen and long wavelength ultraviolet radiation (PUVA) is commonly used to treat psoriasis and vitiligo. These vastly different diseases respond to the therapy by different mechanisms even though the immediate effects of the therapy - photoadduct formation - is the same for both. Because psoriasis is not cured by PUVA, patients receive many treatments over their lifetime and develop a significant risk for the development of skin cancers (primarily squamous cell carcinomas). In this review the basic aspects of psoralen photobiology are reviewed briefly. In addition the impact of the analysis of mutations in the tumor suppressor gene, p53, are summarized. An unexpected mutation spectrum (very few T-->A transversions and frequent UVB signature C-->T transitions) suggest that effects other than direct DNA photoadduct formation may be at play. The roles of reactive oxygen species-induced base changes as well as other clastogenic factors are discussed. This analysis suggests that it may be possible to improve the therapeutic efficacy of PUVA by a careful evaluation of the mode of delivery.

Light and death: photons and apoptosis

Phototherapies like photodynamic therapy (PDT), UVA1, UVB, and PUVA treat skin diseases. These phototherapies work because they alter cytokine profiles, change immune cytotoxicity in the skin, and directly kill diseased cells by apoptosis. Apoptosis is a term that only describes the morphologic changes a cell undergoes during this mode of cell death. The terms "immediate", "intermediate", and "delayed" apoptosis segregate the different apoptotic mechanisms into three kinetic categories, whereas the terms preprogrammed cell death (pre-PCD) and programmed cell death (PCD) describe the underlying mechanisms. Immediate apoptosis (T< or =0.5 h post-exposure) is triggered by singlet-oxygen damage that opens the mitochondrial megachannel, which can be mediated by PDT or UVA1 radiation. It is a pre-PCD mechanism of apoptosis, i.e., protein synthesis is not required post-insult, because all the necessary components are constitutively synthesized and only need to be activated. Intermediate apoptosis (T< or =4 h>0.5 h) is initiated by receptor cross-linking on the plasma membrane, which can be achieved using high doses of UVB or UVC radiation. It is also a pre-PCD mechanism. Delayed apoptosis (T>4 h) is induced by DNA damage that can be caused by X-rays, PUVA, UVC, UVB, UVA, and PDT. It is a PCD mechanism of apoptosis, i.e., protein synthesis is required post-insult. These three apoptotic mechanisms each access one of two "points-of-no-return" located on the mitochondrial membrane, which activate different, but not mutually exclusive, final pathways of apoptosis. This review discusses the latest findings on these apoptotic mechanisms and their implications in phototherapies.