The spectrum of pathogenic mutations in SPINK5 in 19 families with Netherton syndrome: implications for mutation detection and first case of prenatal diagnosis

Epidermal barrier dysfunction in atopic dermatitis

Atopic dermatitis (AD) is a multifactorial, heterogenous disease that arises as a result of the interaction between both environmental and genetic factors. Changes in at least three groups of genes encoding structural proteins, epidermal proteases, and protease inhibitors predispose to a defective epidermal barrier and increase the risk of developing AD. Loss-of-function mutations found within the FLG gene encoding the structural protein, filaggrin, represent the most significant genetic factor predisposing to AD identified to date. Enhanced protease activity and decreased synthesis of the lipid lamellae lead to exacerbated breakdown of the epidermal barrier. Environmental factors, including the use of soap and detergents, exacerbate epidermal barrier breakdown, attributed to the elevation of stratum corneum pH. A sustained increase in pH enhances the activity of degradatory proteases and decreases the activity of the lipid synthesis enzymes. The strong association between both genetic barrier defects and environmental insults to the barrier with AD suggests that epidermal barrier dysfunction is a primary event in the development of this disease. Our understanding of gene-environment interactions should lead to a better use of some topical products, avoidance of others, and the increased use and development of products that can repair the skin barrier.

Evaluation and clinical interpretation of hypergammaglobulinemia E: differentiating atopy from immunodeficiency

Increases in total serum IgE levels can be observed in many diverse conditions, from infection to atopy to primary immunodeficiency. The differentiation of atopy from immunodeficiency most often is made on a clinical basis, after taking findings from history, physical examination, and laboratory studies into consideration. However, total IgE level is neither a sensitive nor a specific diagnostic marker for any particular disease and, therefore, should not be relied on to establish a diagnosis of either atopy or primary immunodeficiency.

An infant with Netherton syndrome and persistent pulmonary hypertension requiring extracorporeal membrane oxygenation

Netherton syndrome is a rare genodermatosis characterized by ichthyosiform scaling, hair shaft abnormalities, and atopic features. Affected infants typically have delayed growth and development, immune abnormalities with recurrent infections, and intermittent aminoaciduria. We report a 23-day-old girl who presented with severe primary pulmonary hypertension, exfoliative erythroderma, and trichorrhexis invaginata. Genetic studies confirmed a premature termination mutation R350X in exon 12 of SPINK5. This mutation further supports the genotypic-phenotypic prediction that severe sequela result from premature termination mutations. To our knowledge, this is the first instance of Netherton syndrome associated with primary pulmonary hypertension to be reported. Further postulated is a possible link between excessive desquamation of fetal skin and respiratory failure in a neonate with Netherton syndrome.

New insights into the functional mechanisms and clinical applications of the kallikrein-related peptidase family

The Kallikrein-related peptidase (KLK) family consists of fifteen conserved serine proteases that form the largest contiguous cluster of proteases in the human genome. While primarily recognized for their clinical utilities as potential disease biomarkers, new compelling evidence suggests that this family plays a significant role in various physiological processes, including skin desquamation, semen liquefaction, neural plasticity, and body fluid homeostasis. KLK activation is believed to be mediated through highly organized proteolytic cascades, regulated through a series of feedback loops, inhibitors, auto-degradation and internal cleavages. Gene expression is mainly hormone-dependent, even though transcriptional epigenetic regulation has also been reported. These regulatory mechanisms are integrated with various signaling pathways to mediate multiple functions. Dysregulation of these pathways has been implicated in a large number of neoplastic and non-neoplastic pathological conditions. This review highlights our current knowledge of structural/phylogenetic features, functional role and regulatory/signaling mechanisms of this important family of enzymes.

SPINK5 gene mutation and decreased LEKTI activity in three Chinese patients with Netherton's syndrome

Netherton's syndrome is a rare autosomal recessive disorder caused by mutations of the SPINK5 gene, which encodes the lymphoepithelial Kazal-type-related inhibitor (LEKTI) protein. We observed microstructural changes and detected LEKTI activity and SPINK5 gene mutation in three Chinese patients with Netherton's syndrome. Decreased LEKTI activity was found in the skin of patients. Lamellar bodies and foci of electron-dense material were detected in the intercellular spaces of the stratum corneum. A novel homozygous splicing mutation of 1430+2 T-->G was found in the SPINK5 gene in one proband. No mutation was found in the other family.

Diagnóstico pré-natal das genodermatoses

O diagnóstico pré-natal está indicado para algumas genodermatoses graves, como a epidermólise bolhosa distrófica recessiva e a epidermólise bolhosa juncional. A biópsia de pele fetal foi introduzida em 1980, mas não pode ser realizada antes da 15a semana de gestação. A análise do DNA fetal é método preciso e pode ser realizado mais precocemente na gestação. No entanto, deve-se conhecer a base molecular da genodermatose, e é essencial determinar a mutação e/ou marcadores informativos nas famílias com criança previamente afetada. O DNA fetal pode ser obtido pela biópsia da vilosidade coriônica ou amniocentese. O diagnóstico genético pré-implantação tem surgido como alternativa que dispensa a interrupção da gestação. Essa técnica, que envolve fertilização in vitro e teste genético do embrião. vem sendo realizada para genodermatoses em poucos centros de referência. A ultra-sonografia é exame não invasivo, mas tem uso limitado no diagnóstico pré-natal de genodermatoses. A ultrasonografia tridimensional geralmente estabelece o diagnóstico tardiamente na gestação, e há apenas relatos anedóticos de diagnóstico pré-natal de genodermatoses usando esse método.

Netherton syndrome: mutation analysis of two Taiwanese families

Netherton syndrome (NS) is a severe autosomal recessive skin disorder characterized by congenital ichthyosiform erythroderma, hair shaft abnormalities, and atopic diathesis. Recently, pathogenic mutations were identified in serine protease inhibitor Kazal-type 5 (SPINK5), the gene that encodes lympho-epithelial Kazal-type related inhibitor (LEKTI), a type of serine protease inhibitor involved in the regulation of skin barrier formation and immunity. In the present report, we describe the mutation analysis of two Taiwanese patients with NS. Patient 1 has heterozygous mutations; the maternal allele has novel T808I (C-T transition in codon 808) and the paternal allele has recurrent R790X (C-T transition in codon 790). Patient 2 is homozygous for a novel polymorphism R267Q (G-A transition in codon 267). The change was not detected in the patient's father. Haplotype analysis revealed that the patient was homozygous for the 5 single nucleotide polymorphisms in the genomic sequence of SPINK5 as well as the flanking (GT)(17) and D5S413, in addition to the discrepancy of R267Q. Nevertheless real-time quantitative PCR analysis revealed no microdeletion in the genomic sequence of SPINK5. Thus uniparental disomy of maternal SPINK5 allele was indicated.

Netherton syndrome: Successful use of topical tacrolimus and pimecrolimus in four siblings

Netherton's syndrome (NS) is a rare autosomal recessive disease comprised of ichthyosis in the form of ichthyosis linearis circumflexa, hair shaft defects and atopic manifestations with an elevated IgE level. Various therapeutic options have been used in NS with variable success. Tacrolimus and pimecrolimus belong to the family of calcineurin inhibitors. They bind cytoplasmic proteins and the resulting complex binds calcineurin, inhibiting its ability to dephosphorylate the nuclear factor of activated T cells, thus suppressing gene transcription. There have been conflicting reports of the usefulness of tacrolimus in NS patients, with systemic absorption being the main adverse outcome. Here we report four Saudi siblings (two boys and two girls) with NS who were treated with topical tacrolimus and pimecrolimus with good control of their skin disease without any toxic effect. To our knowledge, this is the second report of the use of topical pimecrolimus in NS in the English literature.

Proteolytic processing of human growth hormone by multiple tissue kallikreins and regulation by the serine protease inhibitor Kazal-Type5 (SPINK5) protein

BACKGROUND

Human growth hormone (hGH) is naturally present in numerous isoforms, some of which arise from proteolytic processing in both the pituitary and periphery. The nature of the enzymes that proteolytically cleave hGH and the regulation of this process are not fully understood. Our objective is to examine if members of a newly discovered human tissue kallikrein family (KLKs) are expressed in the pituitary and if these enzymes can cleave hGH in-vitro.

METHODS

Expression of 12 of the KLKs (KLKs 4-15) and serine protease inhibitor Kazal-type 5 (SPINK5) genes and their proteins in the pituitary was examined by RT-PCR and immunohistochemistry. Recombinant hGH was digested by various recombinant KLKs and fragments were characterized by N-terminal sequencing. SPINK5 recombinant fragments were used for inhibition of KLK activities.

RESULTS

We here describe for the first time expression of numerous KLKs (KLKs 5-8, 10-14) and SPINK5 in the pituitary. KLK6 and SPINK5 appeared to be localized to hGH-producing cells. KLKs 4-6, 8, 13 and 14 were able to cleave hGH, yielding various isoforms, in vitro. Inhibitor SPINK5 fragments were able to suppress activity of KLKs 4, 5 and 14 in vitro. Based on these data, we propose a model for the proteolytic processing of hGH in the pituitary and the regulation of this system by SPINK5 inhibitory domains. We speculate that loss of SPINK5 inhibitory domains, as in the case of Netherton syndrome, may lead to proteolytic over-processing of hGH and to growth retardation.

CONCLUSION

We conclude that many KLKs and SPINK5 are expressed in the pituitary. This serine protease-inhibitor system is likely to participate in the regulated proteolytic processing of hGH in the pituitary, leading to generation of hGH fragments. Our data suggest that KLKs 5, 6 and 14 might be involved in this process.

A potential role for multiple tissue kallikrein serine proteases in epidermal desquamation

Desquamation of the stratum corneum is a serine protease-dependent process. Two members of the human tissue kallikrein (KLK) family of (chymo)tryptic-like serine proteases, KLK5 and KLK7, are implicated in desquamation by digestion of (corneo)desmosomes and inhibition by desquamation-related serine protease inhibitors (SPIs). However, the epidermal localization and specificity of additional KLKs also supports a role for these enzymes in desquamation. This study aims to delineate the probable contribution of KLK1, KLK5, KLK6, KLK13, and KLK14 to desquamation by examining their interactions, in vitro, with: 1) colocalized SPI, lympho-epithelial Kazal-type-related inhibitor (LEKTI, four recombinant fragments containing inhibitory domains 1-6 (rLEKTI(1-6)), domains 6-8 and partial domain 9 (rLEKTI(6-9')), domains 9-12 (rLEKTI(9-12)), and domains 12-15 (rLEKTI(12-15)), secretory leukocyte protease inhibitor, and elafin and 2) their ability to digest the (corneo)desmosomal cadherin, desmoglein 1. KLK1 was not inhibited by any SPI tested. KLK5, KLK6, KLK13, and KLK14 were potently inhibited by rLEKTI(1-6), rLEKTI(6-9'), and rLEKTI(9-12) with Ki values in the range of 2.3-28.4 nm, 6.1-221 nm, and 2.7-416 nm for each respective fragment. Only KLK5 was inhibited by rLEKTI(12-15) (Ki = 21.8 nm). No KLK was inhibited by secretory leukocyte protease inhibitor or elafin. Apart from KLK13, all KLKs digested the ectodomain of desmoglein 1 within cadherin repeats, Ca2+ binding sites, or in the juxtamembrane region. Our study indicates that multiple KLKs may participate in desquamation through cleavage of desmoglein 1 and regulation by LEKTI. These findings may have clinical implications for the treatment of skin disorders in which KLK activity is elevated.

Síndrome de Netherton com 20 anos de acompanhamento

A síndrome de Netherton é doença cutânea autossômica recessiva caracterizada por eritrodermia congênita, anormalidade específica dos pêlos denominada tricorrexe invaginada e manifestações atópicas. Os autores relatam acompanhamento de mais de 20 anos de paciente com essa doença e a melhora importante do cabelo com o uso de Acitretina.

Advances in understanding the genetic basis of inherited single gene skin barrier disorders: new clues to key genes that may be involved in the pathogenesis of atopic dermatitis

Increasing knowledge of genomic DNA sequences and genetic databases has led to the characterization of the molecular basis of several inherited skin disorders. In this review we summarize some of the major recent discoveries that have been made in defining the pathogenic mutations that cause inherited disorders of the skin barrier leading to skin scaling or increased transepidermal water loss in either rare disorders (Netherton’s syndrome or harlequin ichthyosis) or more common genodermatoses (ichthyosis vulgaris). These molecular breakthroughs have led to more accurate diagnoses, better genetic counselling and, where appropriate, the feasibility of DNA-based prenatal diagnosis, as well as the possibility of developing newer forms of treatment, including gene or protein therapy. Identifying the molecular basis of these conditions, especially ichthyosis vulgaris, has also provided dramatic new insight into the genetic abnormalities in the common disorder, atopic dermatitis. Thus research on the relatively rare single gene inherited skin disorders not only has benefits for patients and their families with these uncommon conditions but also has the potential to yield fresh and significant new information about very common skin diseases.

A case of a Japanese neonate with congenital ichthyosiform erythroderma diagnosed as Netherton syndrome

We report a 6-day-old Japanese girl showing generalized erythroderma accompanied by yellowish, exfoliative scaling that was accentuated on the face and scalp. Histological analysis showed psoriasiform dermatitis with acanthotic epidermis and premature shedding of the stratum corneum. Measurement of trypsin-like hydrolytic activity in SC showed six-fold greater activity compared with age-matched controls. DNA analysis revealed two mutations, 375delAT and 966insC, in exons 5 and 11, respectively, of the SPINK5 gene. Although at 4 weeks the child was still too young to display characteristic hair abnormalities or atopic diathesis, we diagnosed Netherton syndrome based on enzyme assay and DNA analysis.

Corneodesmosomal cadherins are preferential targets of stratum corneum trypsin- and chymotrypsin-like hyperactivity in Netherton syndrome

SPINK5 (serine protease inhibitor Kazal-type 5), encoding the protease inhibitor LEKTI (lympho-epithelial Kazal-type related inhibitor), is the defective gene in Netherton syndrome (NS), a severe inherited keratinizing disorder. We have recently demonstrated epidermal protease hyperactivity in Spink5(-/-) mice resulting in desmosomal protein degradation. Herein, we investigated the molecular mechanism underlying the epidermal defect in 15 patients with NS. We demonstrated that, in a majority of patients, desmoglein 1 (Dsg1) and desmocollin 1 (Dsc1) were dramatically reduced in the upper most living layers of the epidermis. These defects were associated with premature degradation of corneodesmosomes. Stratum corneum tryptic enzyme (SCTE)-like and stratum corneum chymotryptic enzyme (SCCE)-like activities were increased, suggesting that these proteases participate in the premature degradation of corneodesmosomal cadherins. SCTE and SCCE expression was extended to the cell layers where Dsg1 and Dsc1 immunostaining was reduced. In contrast, a subset of six patients with normal epidermal protease activity or residual LEKTI expression displayed apparently normal cadherin expression and less severe disease manifestations. This suggests a degree of correlation between cadherin degradation and clinical severity. This work further supports the implication of premature corneodesmosomal cadherin degradation in the pathogenesis of NS and provides evidence for additional factors playing a role in disease expression.

Serine protease activity and residual LEKTI expression determine phenotype in Netherton syndrome

Mutations in the SPINK5 gene encoding the serine protease (SP) inhibitor, lymphoepithelial-Kazal-type 5 inhibitor (LEKTI), cause Netherton syndrome (NS), a life-threatening disease, owing to proteolysis of the stratum corneum (SC). We assessed here the basis for phenotypic variations in nine patients with "mild", "moderate", and "severe" NS. The magnitude of SP activation correlated with both the barrier defect and clinical severity, and inversely with residual LEKTI expression. LEKTI co-localizes within the SC with kallikreins 5 and 7 and inhibits both SP. The permeability barrier abnormality in NS was further linked to SC thinning and proteolysis of two lipid hydrolases (beta-glucocerebrosidase and acidic sphingomyelinase), with resultant disorganization of extracellular lamellar membranes. SC attenuation correlated with phenotype-dependent, SP activation, and loss of corneodesmosomes, owing to desmoglein (DSG)1 and desmocollin (DSC)1 degradation. Although excess SP activity extended into the nucleated layers in NS, degrading desmosomal mid-line structures with loss of DSG1/DSC1, the integrity of the nucleated epidermis appears to be maintained by compensatory upregulation of DSG3/DSC3. Maintenance of sufficient permeability barrier function for survival correlated with a compensatory acceleration of lamellar body secretion, providing a partial permeability barrier in NS. These studies provide a mechanistic basis for phenotypic variations in NS, and describe compensatory mechanisms that permit survival of NS patients in the face of unrelenting SP attack.

Kallikrein-related peptidase 14 may be a major contributor to trypsin-like proteolytic activity in human stratum corneum

We have previously presented evidence that two human kallikrein-related peptidases, KLK5 (hK5, stratum corneum tryptic enzyme, SCTE) and KLK7 (hK7, stratum corneum chymotryptic enzyme, SCCE), which are abundant in the stratum corneum, may be involved in desquamation. Since we had noted that not all trypsin-like activity in the plantar stratum corneum could be ascribed to KLK5, we set out to identify other skin proteases with similar primary substrate specificity. Here we describe purification of a protease identified as KLK14 from plantar stratum corneum, and show that this enzyme may be responsible for as much as 50% of the total trypsin-like activity in this tissue, measured as activity towards a chromogenic substrate cleaved by a wide variety of enzymes with trypsin-like specificity. This was in spite of very low levels of KLK14 protein compared to KLK5 and KLK7. KLK14 could be detected by immunoblotting in normal superficial stratum corneum of all individuals examined. The majority of KLK14 in the plantar stratum corneum is present in its catalytically active form. KLK14 could be immunohistochemically detected in sweat ducts, preferentially in the intraepidermal parts (the acrosyringium), and in sweat glands. The role played by this very efficient protease under normal and disease conditions in the skin remains to be elucidated.

Netherton syndrome in two Japanese siblings with a novel mutation in the SPINK5 gene: immunohistochemical studies of LEKTI and other epidermal molecules

BACKGROUND

Netherton syndrome (NS) is a severe autosomal recessive disorder characterized by ichthyosiform erythroderma, bamboo hair and atopy. The disease is caused by mutations in the SPINK5 gene, which encodes a putative serine protease inhibitor, LEKTI (lymphoepithelial Kazal-type-related inhibitor). Previous studies have clearly shown a crucial role for LEKTI in skin barrier formation.

OBJECTIVES

To identify pathogenic mutations in two Japanese siblings with NS, and further to investigate the consequences of the mutations at the protein level.

METHODS

To screen for mutations in the SPINK5 gene, all of its exons and splice junctions were amplified by polymerase chain reaction and directly sequenced. In addition, immunohistochemical staining of LEKTI, desmoglein (Dsg) 1 and elafin was performed with their specific antibodies.

RESULTS

Mutation analysis resulted in the identification of compound heterozygous mutations, Q713X and R790X, in the SPINK5 gene of both patients. The former one is a novel mutation. Immunohistochemical studies in one patient demonstrated a complete absence of LEKTI and a strong expression of elafin in the patient's skin. Dsg1 was normally expressed in our patient.

CONCLUSIONS

In this report, we describe compound heterozygous mutations in the SPINK5 gene in two Japanese siblings with NS. The result of immunohistochemistry shows LEKTI deficiency and upregulation of elafin in the skin of one patient. Furthermore, our data indicate that degradation of Dsg1 does not always occur in NS.

Common variable immunodeficiency: test indications and interpretations

Common variable immunodeficiency (CVID) is a primary immunodeficiency disorder that can present with multiple phenotypes, all of which are characterized by hypogammaglobulinemia, in a person at any age. A specific genetic defect that accounts for all CVID phenotypes has not been identified, and it is likely that several distinct genetic disorders with similar clinical presentations are responsible for the observed variation. In this review, we summarize the known genetic mutations that give rise to hypogammaglobulinemia and how these gene products affect normal or abnormal B-cell development and function, with particular emphasis on CVID. Additionally, we describe specific phenotypic and genetic laboratory tests that can be used to diagnose CVID and provide guidelines for test interpretation and subsequent therapeutic intervention.

A Japanese infant with localized ichthyosis linearis circumflexa on the palms and soles harbouring a compound heterozygous mutation in the SPINK5 gene

We report a 6-month-old Japanese boy showing ichthyosis linearis circumflexa localized on the palms and soles. He showed bamboo hairs and aminoaciduria, and was positive for cow's milk and egg IgE antibodies by radioallergosorbent tests. Trypsin-like hydrolytic activity in the patient's lesional stratum corneum showed an activity seven times higher than that in age-matched controls. DNA analysis showed that the patient harboured the compound heterozygous mutations R790X and 1220+1 G-->C in the SPINK5 gene, compatible with the diagnosis of Netherton syndrome (NS). As the genotype/phenotype correlations in NS have not yet been fully clarified, the position of the premature termination codon in the SPINK5 gene may contribute to explain such a mild form of NS in our patient.

Netherton Syndrome with Extensive Skin Peeling and Failure to Thrive due to a Homozygous Frameshift Mutation in SPINK5

BACKGROUND

Netherton syndrome (NTS) is a rare autosomal recessive multisystem disorder characterized by congenital erythroderma and ichthyosis, hair shaft abnormalities and immune dysregulation. The disorder is caused by deleterious mutations in the SPINK5 gene, encoding the serine protease inhibitor LEKTI.

OBJECTIVE

Our objective was to investigate if the erythrodermic variant of peeling skin syndrome is also caused by SPINK5 mutations and to study the consequences of the disease on infantile brain development.

METHODS

In an infant with extensive erythroderma, peeling skin and failure to thrive, we analyzed the SPINK5 gene for pathogenic mutations by direct DNA sequencing and performed repeated brain MRI studies with diffusion-weighted imaging.

RESULTS

We identified a homozygous 4-base-pair insertion in exon 5 of SPINK5, which introduces a premature termination codon and appears to be a common mutation among West Indies islanders. MRI analyses revealed a persistent diffuse volume loss.

CONCLUSION

Our results confirm that early truncation mutations of the coding sequence of SPINK5 produce a severe phenotype and that generalized peeling skin is one of the manifestations of NTS. We further demonstrate for the first time that NTS may be associated with MRI abnormalities indicative of a permanent tissue injury of the brain.

Molecular genetics of the ichthyoses

The ichthyoses are a large, clinically, genetically, and etiologically heterogeneous group of disorders of cornification due to abnormal differentiation and desquamation of the epidermis. Although they differ in clinical features, inheritance, and structural and biochemical abnormalities of the epidermis, they often pose a diagnostic challenge. For each of the 12 ichthyoses and related disorders described here, the major disease genes have been identified and genotype-phenotype correlation have begun to emerge. The molecular findings reveal the functional importance and interactions of many different epidermal proteins and metabolic pathways, including major structural proteins (keratins, loricrin), enzymes involved in lipid metabolism (transglutaminase 1, lipoxygenases, fatty aldehyde dehydrogenase, steroid sulfatase, glucocerebrosidase, Delta8-Delta7 sterol isomerase, 3beta-hydroxysteroid dehydrogenase), and protein catabolism (LEKTI), peroxisomal transport and processing (Peroxin 7 receptor, Phytanoyl-CoA hydroxylase) and DNA repair (proteins of the transcription repair complex). This review highlights the spectacular advances in the molecular genetics and biology of heritable ichthyoses over the past decade. It illustrates the power of molecular diagnostics for refining disease classification, providing prenatal diagnosis, improving genetic counseling, and clinical management.

LEKTI is localized in lamellar granules, separated from KLK5 and KLK7, and is secreted in the extracellular spaces of the superficial stratum granulosum

Lympho-epithelial Kazal-type-related inhibitor (LEKTI) is a putative serine protease inhibitor encoded by serine protease inhibitor Kazal-type 5 (SPINK5). It is strongly expressed in differentiated keratinocytes in normal skin but expression is markedly reduced or absent in Netherton syndrome (NS), a severe ichthyosis caused by SPINK5 mutations. At present, however, both the precise intracellular localization and biological roles of LEKTI are not known. To understand the functional role of LEKTI, we examined the localization of LEKTI together with kallikrein (KLK)7 and KLK5, possible targets of LEKTI, in the human epidermis, by confocal laser scanning microscopy and immunoelectron microscopy. In normal skin, LEKTI, KLK7, and KLK5 were all found in the lamellar granule (LG) system, but were separately localized. LEKTI was expressed earlier than KLK7 and KLK5. In NS skin, LEKTI was absent and an abnormal split in the superficial stratum granulosum was seen in three of four cases. Collectively, these results suggest that in normal skin the LG system transports and secretes LEKTI earlier than KLK7 and KLK5 preventing premature loss of stratum corneum integrity/cohesion. Our data provide new insights into the biological functions of LG and the pathogenesis of NS.

Netherton syndrome: report of two Taiwanese siblings with staphylococcal scalded skin syndrome and mutation ofSPINK5

Netherton syndrome (NS) is a severe autosomal recessive ichthyosis. It is characterized by congenital ichthyosiform erythroderma, trichorrhexis invaginata, ichthyosis linearis circumflexa, atopic diathesis and frequent bacterial infections. Pathogenic mutations in SPINK5 have recently been identified in NS. SPINK5 encodes lymphoepithelial Kazal-type-related inhibitor (LEKTI), a new type of serine protease inhibitor involved in the regulation of skin barrier formation and immunity. We report two Taiwanese brothers with NS. The patients had typical manifestations of NS with an atopic diathesis and recurrent staphylococcal infections, including staphylococcal scalded skin syndrome (SSSS) since birth. Horny layers were obtained by skin surface biopsy for electron microscopy from lesional skin of both patients and from normal controls. All 33 exons and flanking intron boundaries of SPINK5 were amplified for direct sequencing. The ultrastructure of the stratum corneum (SC) was characterized by premature degradation of corneodesmosomes (CDs) with separation of corneocytes. A homozygous 2260A --> T (K754X) mutation of SPINK5 was found in both patients. Staphylococcal exfoliative toxin A (ETA) is a serine protease capable of cleaving desmoglein 1, an important adhesive molecule of CDs, and can cause separation of the SC, resulting in SSSS. The premature degradation of CDs found in our patients may be attributable to insufficient LEKTI, and possibly also to colonization/infection of ETA-producing Staphylococcus aureus. Mechanisms involved in the pathogenesis of the skin barrier defect in NS are proposed. Further study is needed to prove this hypothesis.

Genetic hair and nail disorders

Hair and nails are skin appendages that share with other ectodermal tissues a common developmental pathway. Inherited disorders affecting these two structures therefore very often involve other epithelial components and present with multiple anomalies, generating both physical and psychological distress among patients and their families. The present review briefly describes major recent advances in our understanding of hair and nail genodermatoses.

Spink5-deficient mice mimic Netherton syndrome through degradation of desmoglein 1 by epidermal protease hyperactivity

Mutations in SPINK5, encoding the serine protease inhibitor LEKTI, cause Netherton syndrome, a severe autosomal recessive genodermatosis. Spink5(-/-) mice faithfully replicate key features of Netherton syndrome, including altered desquamation, impaired keratinization, hair malformation and a skin barrier defect. LEKTI deficiency causes abnormal desmosome cleavage in the upper granular layer through degradation of desmoglein 1 due to stratum corneum tryptic enzyme and stratum corneum chymotryptic enzyme-like hyperactivity. This leads to defective stratum corneum adhesion and resultant loss of skin barrier function. Profilaggrin processing is increased and implicates LEKTI in the cornification process. This work identifies LEKTI as a key regulator of epidermal protease activity and degradation of desmoglein 1 as the primary pathogenic event in Netherton syndrome.

Epidermal detachment, desmosomal dissociation, and destabilization of corneodesmosin in Spink5-/- mice

Netherton syndrome (NS) is a human autosomal recessive skin disease caused by mutations in the SPINK5 gene, which encodes the putative proteinase inhibitor LEKTI. We have generated a transgenic mouse line with an insertional mutation that inactivated the mouse SPINK5 ortholog. Mutant mice exhibit fragile stratum corneum and perinatal death due to dehydration. Our analysis suggests that the phenotype is a consequence of desmosomal fragility associated with premature proteolysis of corneodesmosin, an extracellular desmosomal component. Our mouse mutant provides a model system for molecular studies of desmosomal stability and keratinocyte adhesion, and for designing therapeutic strategies to treat NS.

SPINK5 and Netherton Syndrome: Novel Mutations, Demonstration of Missing LEKTI, and Differential Expression of Transglutaminases

Netherton syndrome (NTS) is an autosomal recessive congenital ichthyosis featuring chronic inflammation of the skin, hair anomalies, epidermal hyperplasia with an impaired epidermal barrier function, failure to thrive and atopic manifestations. The disease is caused by mutations in the SPINK5 gene encoding the serine proteinase inhibitor lympho-epithelial Kazal-type inhibitor (LEKTI). Sequence analyses of SPINK5 in seven NTS patients from five different families allowed us to identify two known and three novel mutations all creating premature termination codons. We developed a monoclonal antibody giving a strong signal for LEKTI in the stratum granulosum of normal skin and demonstrated absence of the protein in NTS epidermis. Immunoblot analysis revealed presence of full length LEKTI and of LEKTI cleavage fragments in normal hair roots, whereas in NTS hair roots LEKTI and its cleavage products were completely missing. Transglutaminase1 activity was present throughout almost the entire suprabasal epidermis in NTS, whereas in normal skin it is restricted to the stratum granulosum. In contrast, immunostaining for transglutaminase3 was absent or faint. Moreover, comparable with the altered pattern in psoriatic skin the epidermis in NTS strongly expressed the serine proteinase inhibitor SKALP/elafin and the anti-microbial protein human beta-defensin 2. These studies demonstrate LEKTI deficiency in the epidermis and in hair roots at the protein level and an aberrant expression of other proteins, especially transglutaminase1 and 3, which may account for the impaired epidermal barrier in NTS.

Deleterious mutations in SPINK5 in a patient with congenital ichthyosiform erythroderma: molecular testing as a helpful diagnostic tool for Netherton syndrome

The congenital erythrodermas represent a heterogeneous group of inherited and acquired disorders often accompanied by systemic infections, impaired epidermal barrier function and concomitant life-threatening fluid and electrolyte imbalance. In the present report, we describe a patient who was considered to have congenital ichthyosiform erythroderma for 26 years until molecular testing led to the correct diagnosis of Netherton syndrome.

Expression of LEKTI domains 6-9' in the baculovirus expression system: recombinant LEKTI domains 6-9' inhibit trypsin and subtilisin A

The precursor lympho-epithelial Kazal-type-related inhibitor (LEKTI), containing two Kazal-type and 13 nonKazal-type domains, is an efficient inhibitor of multiple serine proteinases, among them plasmin, subtilisin A, cathepsin G, elastase, and trypsin. To gain insight into the structure and function of some of these domains, a portion of the cDNA coding for LEKTI domains 6-9' was cloned and expressed in Sf9 cells using the baculovirus expression vector system (BEVS). Through a single purification step using a Co2+ column, 3-4 mg of purified recombinant LEKTI-domains 6-9' (rLEKTI6-9') with the predicted molecular mass of 34.6 kDa was obtained from the cell pellet of a 1-L culture. Unlike full-length LEKTI, rLEKTI6-9' inhibited trypsin and subtilisin A but not plasmin, cathepsin G, or elastase. The inhibition of trypsin and subtilisin A by rLEKTI6-9' occurred through a noncompetitive mechanism, with inhibitory constants (Ki) of 356 +/- 12 and 193 +/- 10 nM, respectively. On the basis of the Ki values, rLEKTI6-9' was determined to be a more potent trypsin inhibitor and a less potent subtilisin A inhibitor than the full-length LEKTI. In contrast to LEKTI domains 6-9', recombinant LEKTI domain 6 does not inhibit subtilisin A but competitively inhibited trypsin with a Ki of 200 +/- 10 nM. Taking LEKTI6-9' as an example, the BEVS should facilitate the structure-function analysis of naturally occurring processed LEKTI forms that have physiological relevance.

Early development of multiple epithelial neoplasms in Netherton syndrome

We report a case of Netherton syndrome manifested as congenital ichthyosiform erythroderma, trichorrhexis invaginata and atopy, who in early adulthood developed multiple, aggressive epithelial neoplasms in sun-exposed areas of the skin, in areas with papillomatous skin hyperplasia and at the left parotid region. The occurrence of cutaneous neoplasia has been reported in syndromes with congenital ichthyosis and suggests that the underlying genetic defects may cause the development of cancer in prone patients.

Homologous proteins with different folds: the three-dimensional structures of domains 1 and 6 of the multiple Kazal-type inhibitor LEKTI

We have determined the solution structures of recombinant domain 1 and native domain 6 of the multi-domain Kazal-type serine proteinase inhibitor LEKTI using multi-dimensional NMR spectroscopy. While two of the 15 potential inhibitory LEKTI domains contain three disulfide bonds typical of Kazal-type inhibitors, the remaining 13 domains have only two of these disulfide bridges. Therefore, they may represent a novel type of serine proteinase inhibitor. The first and the sixth LEKTI domain, which have been isolated from human blood ultrafiltrate, belong to this group. In spite of sharing the same disulfide pattern and a sequence identity of about 35% from the first to the fourth cysteine, the two proteins show different structures in this region. The three-dimensional structure of domain 6 consists of two helices and a beta-hairpin structure, and closely resembles the three-dimensional fold of classical Kazal-type serine proteinase inhibitors including the inhibitory binding loop. Domain 6 has been shown to be an efficient, but non-permanent serine proteinase inhibitor. The backbone geometry of its canonical loop is not as well defined as the remaining structural elements, providing a possible explanation for its non-permanent inhibitory activity. We conclude that domain 6 belongs to a subfamily of classical Kazal-type inhibitors, as the third disulfide bond and a third beta-strand are missing. The three-dimensional structure of domain 1 shows three helices and a beta-hairpin, but the central part of the structure differs remarkably from that of domain 6. The sequence adopting hairpin structure in domain 6 exhibits helical conformation in domain 1, and none of the residues within the putative P3 to P3' stretch features backbone angles that resemble those of the canonical loop of known proteinase inhibitors. No proteinase has been found to be inhibited by domain 1. We conclude that domain 1 adopts a new protein fold and is no canonical serine proteinase inhibitor.

Inhibition of serine proteinases plasmin, trypsin, subtilisin A, cathepsin G, and elastase by LEKTI: a kinetic analysis

The human LEKTI gene encodes a putative 15-domain serine proteinase inhibitor and has been linked to the inherited disorder known as Netherton syndrome. In this study, human recombinant LEKTI (rLEKTI) was purified using a baculovirus/insect cell expression system, and the inhibitory profile of the full-length rLEKTI protein was examined. Expression of LEKTI in Sf9 cells showed the presence of disulfide bonds, suggesting the maintenance of the tertiary protein structure. rLEKTI inhibited the serine proteinases plasmin, subtilisin A, cathepsin G, human neutrophil elastase, and trypsin, but not chymotrypsin. Moreover, rLEKTI did not inhibit the cysteine proteinase papain or cathepsin K, L, or S. Further, rLEKTI inhibitory activity was inactivated by treatment with 20 mM DTT, suggesting that disulfide bonds are important to LEKTI function. The inhibition of plasmin, subtilisin A, cathepsin G, elastase, and trypsin by rLEKTI occurred through a noncompetitive-type mechanism, with inhibitory constants (K(i)) of 27 +/- 5, 49 +/- 3, 67 +/- 6, 317 +/-36, and 849 +/- 55 nM, respectively. Thus, LEKTI is likely to be a major physiological inhibitor of multiple serine proteinases.

Progress in molecular genetics of heritable skin diseases: the paradigms of epidermolysis bullosa and pseudoxanthoma elasticum

The 42nd Annual Symposium on the Biology of the Skin, entitled "The Genetics of Skin Disease", was held in Snowmass Village, Colorado, in July 1993. That meeting presented the opportunity to discuss how modern approaches to molecular genetics and molecular biology could be applied to understanding the mechanisms of skin diseases. The published proceedings of this meeting stated that "It is an opportune time to examine the genetics of skin disease" (Norris et al, 1994). Indeed, this meeting just caught the wave of early pioneering studies that have helped us to understand the molecular basis of a large number of genodermatoses. This overview presented in the 50th Annual Symposium on the biology of the skin, highlights the progress made in the molecular genetics of heritable skin diseases over the past decade.

International nosology and classification of constitutional disorders of bone (2001)

The last International Classification of Constitutional Disorders of Bone was published in 1998. Since then rapid advances have been made in identifying the molecular changes responsible for defined conditions and new disorders are constantly being delineated. For these reasons a further update on the classification is appropriate. It has been expended to not only the osteochondrodysplasias (33 groups) but also genetically determined dysostoses (3 groups).

Squamous cell carcinoma in a patient with Netherton's syndrome

A 29-year-old white woman with a history of Netherton's syndrome presented with two squamous cell carcinomas on the right dorsal hand and the left upper arm. She reported a 2-year history of these lesions, which were originally treated as warts. She denied excessive sun exposure, immunosuppressive therapy, or a previous history of skin cancer. Her past medical history included acute renal failure, multiple urinary tract infections, meningitis, and recurrent otitis media as a child. In addition, she had an ovarian abscess at 4 years of age with resulting salpingo-oophorectomy. She also reported a history of severe myopia, glaucoma, and multiple ocular infections with a resulting corneal scar. In addition to atopic dermatitis, she had a 10-year history of psoriasis. Her medications included topical steroids and emollients for atopic dermatitis and psoriasis, in addition to Timolol ophthalmic drops for glaucoma. Her family history was significant for a 22-year-old sister with Netherton's syndrome (Fig. 1). She denied any history of skin cancer in her sister or other members of her family. On physical examination, she had an exfoliative erythroderma, madarosis, and diffuse patchy alopecia. In the bilateral axilla, she had well-defined pink scaly plaques which were confirmed as psoriasis by biopsy. On the right dorsal hand, she had a 1.5 x 1.0 cm pink verrucous plaque (Fig. 2). On the left upper arm, she had a 1.5 x 0.8 cm pink scaly plaque. Biopsies of both sites confirmed squamous cell carcinomas. Both lesions were completely excised with 4 mm margins.

Epidermal overexpression of stratum corneum chymotryptic enzyme in mice: a model for chronic itchy dermatitis

Identification of tissue-specific mechanisms involved in the pathophysiology of inflammatory skin diseases could offer new possibilities to develop effective therapies with fewer systemic effects. The serine protease stratum corneum chymotryptic enzyme is preferentially expressed in cornifying epithelia. We have previously reported on increased expression of the stratum corneum chymotryptic enzyme in psoriasis. Here is reported an increased epidermal expression of stratum corneum chymotryptic enzyme also found in chronic lesions of atopic dermatitis. Transgenic mice expressing human stratum corneum chymotryptic enzyme in suprabasal epidermal keratinocytes were found to develop pathologic skin changes with increased epidermal thickness, hyperkeratosis, dermal inflammation, and severe pruritus. The results suggest that stratum corneum chymotryptic enzyme may be involved in the pathogenesis of inflammatory skin diseases, and that stratum corneum chymotryptic enzyme and related enzymes should be evaluated as potential targets for new therapies.

Elevated stratum corneum hydrolytic activity in Netherton syndrome suggests an inhibitory regulation of desquamation by SPINK5-derived peptides

Netherton syndrome is a congenital ichthyosis associated with erythroderma, hair shaft defects, and atopic features. The mutations of the secretory serine protease inhibitor Kazal-type 5 gene have been identified in Netherton syndrome patients; however, the actual physiologic substrates of the serine protease inhibitor Kazal-type 5 proprotein are unknown, and how the genetic defects cause characteristic skin phenotype remains uncertain. Here, we describe the serine protease inhibitor Kazal-type 5 gene mutations, including two novel non-sense mutations, and genotype-phenotype correlation in three Netherton syndrome patients in two unrelated Japanese families. Furthermore, based on the reappraisal of the structure of the serine protease inhibitor Kazal-type 5 proprotein, demonstration of the presence of carboxypeptidase in normal keratinocytes, and the observation of mRNA localization of the serine protease inhibitor Kazal-type 5 transcripts in the uppermost epidermis as well as pilosebaceous units, we propose a hypothetical model of proteolytic processing of the serine protease inhibitor Kazal-type 5 proprotein in the epidermis and inhibitory regulation of corneocyte desquamation by a set of serine protease inhibitor Kazal-type 5-derived peptides. This hypothesis is supported by the marked increase of trypsin-like hydrolytic activity demonstrated in stratum corneum samples from our Netherton syndrome patients. The findings in this study suggest that the defective inhibitory regulation of desquamation due to the serine protease inhibitor Kazal-type 5 gene mutations may cause over-desquamation of corneocytes in Netherton syndrome, leading to severe skin permeability barrier dysfunction.

Netherton syndrome: disease expression and spectrum of SPINK5 mutations in 21 families

Netherton syndrome is a severe autosomal recessive skin disorder characterized by congenital erythroderma, a specific hair-shaft abnormality, and atopic manifestations with high IgE levels. Recently, we identified SPINK5, which encodes the serine protease inhibitor Kazal-type 5 protein (LEKTI), as the defective gene in Netherton syndrome. Here we describe the intron-exon organization of the gene and characterize the SPINK5 mutations in patients from 21 families of different geographic origin, using denaturing high performance liquid chromatography and direct sequencing. We identified 18 mutations, of which 13 were novel and seven (39%) were recurrent. The majority of the mutations were clustered between exons 1-8 and exons 21-26. They comprised four nonsense mutations (22%), eight frameshift insertions or deletions (44%), and six splice-site defects (33%). All mutations predict the formation of premature termination codons. Northern blot analysis showed variable reduction of SPINK5 mutant transcript levels, suggesting variable efficiency of nonsense-mediated mRNA decay. Seven patients were homozygotes, eight were compound heterozygotes, and five were heterozygotes with only one identifiable SPINK5 mutation. Five mutations, one of which resulted in perinatal lethal disease in three families, were associated with certain ethnic groups. We also describe 45 intragenic polymorphisms in the patients studied. The clinical features of erythroderma, trichorrhexis invaginata, and atopic manifestations were present in the majority of affected individuals and ichthyosis linearis circumflexa was seen in 12 out of 24 patients. Interfamilial and intrafamilial variation in disease severity was observed, with no clear correlation between mutations and phenotype, suggesting that the degree of severity may be affected by other factors.