Identification of a new splice form of the EDA1 gene permits detection of nearly all X-linked hypohidrotic ectodermal dysplasia mutations

Molecular basis of hypohidrotic ectodermal dysplasia: an update

Recent advances in understanding the molecular events underlying hypohidrotic ectodermal dysplasia (HED) caused by mutations of the genes encoding proteins of the tumor necrosis factor α (TNFα)-related signaling pathway have been presented. These proteins are involved in signal transduction from ectoderm to mesenchyme during development of the fetus and are indispensable for the differentiation of ectoderm-derived structures such as eccrine sweat glands, teeth, hair, skin, and/or nails. Novel data were reviewed and discussed on the structure and functions of the components of TNFα-related signaling pathway, the consequences of mutations of the genes encoding these proteins, and the prospect for further investigations, which might elucidate the origin of HED.

The genetics of human skin disease

The skin is composed of a variety of cell types expressing specific molecules and possessing different properties that facilitate the complex interactions and intercellular communication essential for maintaining the structural integrity of the skin. Importantly, a single mutation in one of these molecules can disrupt the entire organization and function of these essential networks, leading to cell separation, blistering, and other striking phenotypes observed in inherited skin diseases. Over the past several decades, the genetic basis of many monogenic skin diseases has been elucidated using classical genetic techniques. Importantly, the findings from these studies has shed light onto the many classes of molecules and essential genetic as well as molecular interactions that lend the skin its rigid, yet flexible properties. With the advent of the human genome project, next-generation sequencing techniques, as well as several other recently developed methods, tremendous progress has been made in dissecting the genetic architecture of complex, non-Mendelian skin diseases.

Future developments in XLHED treatment approaches

X-linked hypohidrotic ectodermal dysplasia (XLHED) is the most common genetic disorder of ectoderm development, presenting with abnormalities of skin, teeth, hair, and secretory glands. In the first years of life, XLHED-affected patients are at risk for life-threatening hyperthermia and pulmonary infection. Survival into childhood and beyond is associated with severe dental abnormalities as well as chronic growth, respiratory, skin, eye, and psychosocial disorders. Currently there are no approved therapies to restore function in disorders of development like XLHED. Over the last two decades, molecular research has provided convincing evidence that alterations in the ectodysplasin (EDA) gene that disrupt the encoded protein EDA-A1 are causative for XLHED. In mouse and dog XLHED models, administration of a single course of an EDA-A1 replacement protein (EDI200) resulted in permanent correction of the key phenotypic features, providing the first hope for an effective, targeted therapy. Animal models for genetic disorders have their strengths and limitations that must be considered when modeling clinical studies in human patients. Of greatest significance in the case of a developmental disorder may be the relative timeline for normal development and the maturation level at birth. With FDA clearance to start EDI200 studies in XLHED patients, we are on the verge of converting a decade of animal studies into the first test of a novel paradigm for rescue and permanent correction of a human developmental disorder.

Generation and characterization of function-blocking anti-ectodysplasin A (EDA) monoclonal antibodies that induce ectodermal dysplasia

Development of ectodermal appendages, such as hair, teeth, sweat glands, sebaceous glands, and mammary glands, requires the action of the TNF family ligand ectodysplasin A (EDA). Mutations of the X-linked EDA gene cause reduction or absence of many ectodermal appendages and have been identified as a cause of ectodermal dysplasia in humans, mice, dogs, and cattle. We have generated blocking antibodies, raised in Eda-deficient mice, against the conserved, receptor-binding domain of EDA. These antibodies recognize epitopes overlapping the receptor-binding site and prevent EDA from binding and activating EDAR at close to stoichiometric ratios in in vitro binding and activity assays. The antibodies block EDA1 and EDA2 of both mammalian and avian origin and, in vivo, suppress the ability of recombinant Fc-EDA1 to rescue ectodermal dysplasia in Eda-deficient Tabby mice. Moreover, administration of EDA blocking antibodies to pregnant wild type mice induced in developing wild type fetuses a marked and permanent ectodermal dysplasia. These function-blocking anti-EDA antibodies with wide cross-species reactivity will enable study of the developmental and postdevelopmental roles of EDA in a variety of organisms and open the route to therapeutic intervention in conditions in which EDA may be implicated.

Involvement of and interaction between WNT10A and EDA mutations in tooth agenesis cases in the Chinese population

Background

Dental agenesis is the most common, often heritable, developmental anomaly in humans. Although WNT10A gene mutations are known to cause rare syndromes associated with tooth agenesis, including onycho-odontodermal dysplasia (OODD), Schöpf-Schulz-Passarge syndrome (SSPS), hypohidrotic ectodermal dysplasia (HED), and more than half of the cases of isolated oligodontia recently, the genotype-phenotype correlations and the mode of inheritance of WNT10A mutations remain unclear. The phenotypic expression with WNT10A mutations shows a high degree of variability, suggesting that other genes might function with WNT10A in regulating ectodermal organ development. Moreover, the involvement of mutations in other genes, such as EDA, which is also associated with HED and isolated tooth agenesis, is not clear. Therefore, we hypothesized that EDA mutations interact with WNT10A mutations to play a role in tooth agenesis. Additionally, EDA, EDAR, and EDARADD encode signaling molecules in the Eda/Edar/NF-κB signaling pathways, we also checked EDAR and EDARADD in this study.

Methods

WNT10A, EDA, EDAR and EDARADD were sequenced in 88 patients with isolated oligodontia and 26 patients with syndromic tooth agenesis. The structure of two mutated WNT10A and two mutated EDA proteins was analyzed.

Results

Digenic mutations of both WNT10A and EDA were identified in 2 of 88 (2.27%) isolated oligodontia cases and 4 of 26 (15.38%) syndromic tooth agenesis cases. No mutation in EDAR or EDARADD gene was found.

Conclusions

WNT10A and EDA digenic mutations could result in oligodontia and syndromic tooth agenesis in the Chinese population. Moreover, our results will greatly expand the genotypic spectrum of tooth agenesis.

A newly identified missense mutation of the EDA1 gene in a Hungarian patient with Christ-Siemens-Touraine syndrome

Christ-Siemens-Touraine syndrome (CST; OMIM 305100) belongs to the group of ectodermal dysplasias and is characterized by the development of sparse hair, abnormal or missing teeth and sweating deficiency. CST is the consequence of mutations located in the ectodysplasin A (EDA1) gene. We have identified a 35-year-old Hungarian man with characteristic dysmorphic facial features, sparse hair, reduced sweating and missing teeth. Direct sequencing of the coding regions revealed a novel missense mutation in the eighth exon (c.971T/A, p.Val324Glu). The affected patient carries the mutation in a hemizygous form. Previous studies reported the association of missense mutations with non-syndromic tooth agenesis. However, the reported hemizygous patient exhibits hypodontia as well as hypotrichosis and reduced sweating. His daughter, an obligate heterozygous carrier of the identified missense mutation, exhibits only mild teeth abnormalities. As the novel missense mutation is located within the tumor necrosis factor (TNF) domain of the ectodysplasin protein, we hypothesize that this genetic variant affects the ectodysplasin/NFκB signaling pathway.

Candidate gene analysis of tooth agenesis identifies novel mutations in six genes and suggests significant role for WNT and EDA signaling and allele combinations

Failure to develop complete dentition, tooth agenesis, is a common developmental anomaly manifested most often as isolated but also as associated with many developmental syndromes. It typically affects third molars or one or few other permanent teeth but severe agenesis is also relatively prevalent. Here we report mutational analyses of seven candidate genes in a cohort of 127 probands with non-syndromic tooth agenesis. 82 lacked more than five permanent teeth excluding third molars, called as oligodontia. We identified 28 mutations, 17 of which were novel. Together with our previous reports, we have identified two mutations in MSX1, AXIN2 and EDARADD, five in PAX9, four in EDA and EDAR, and nine in WNT10A. They were observed in 58 probands (44%), with a mean number of missing teeth of 11.7 (range 4 to 34). Almost all of these probands had severe agenesis. Only few of the probands but several relatives with heterozygous genotypes of WNT10A or EDAR conformed to the common type of non-syndromic tooth agenesis, incisor-premolar hypodontia. Mutations in MSX1 and PAX9 affected predominantly posterior teeth, whereas both deciduous and permanent incisors were especially sensitive to mutations in EDA and EDAR. Many mutations in EDAR, EDARADD and WNT10A were present in several families. Biallelic or heterozygous genotypes of WNT10A were observed in 32 and hemizygous or heterozygous genotypes of EDA, EDAR or EDARADD in 22 probands. An EDARADD variant were in seven probands present together with variants in EDAR or WNT10A, suggesting combined phenotypic effects of alleles in distinct genes.

Early respiratory and ocular involvement in X-linked hypohidrotic ectodermal dysplasia

X-linked hypohidrotic ectodermal dysplasia (XLHED; ectodysplasin deficiency) has been classically described as affecting hair, sweat glands, and dentition. What may be underappreciated is the effect ectodysplasin deficiency has on glands surrounding the airways and eyes and the resulting chronic health issues. In this study, 12 male children (age range 6-13 years) and 14 male adults with XLHED (18-58 years of age) were investigated by pulmonary function tests, measurement of fractional exhaled nitric oxide, and by ophthalmologic assessments. Twelve healthy individuals (six children, six adults) served as controls. Signs of airway constriction and inflammation were detected in eight children with XLHED, including the youngest subject, and in ten adult XLHED patients. Increased tear osmolarity, reduced tear film break-up time, and other ocular abnormalities were also present at an early age. Five of 12 XLHED subjects not reporting a history of asthma and 7 of the 12 patients not reporting a history of dry eye issues showed at least two abnormal test results in the respective organ system. The presence of residual sweat ducts, suggestive of partial ectodysplasin gene expression, correlated with milder disease in two XLHED subjects with mutations affecting the collagen-like domain of ectodysplasin.

CONCLUSION

The high prevalence of asthma-like symptoms in XLHED patients as young as 6 years and a similar prevalence of dry eye problems indicate that screening evaluation, regular monitoring, and consideration of therapeutic intervention should begin in early childhood.

Methylation state of the EDA gene promoter in Chinese X-linked hypohidrotic ectodermal dysplasia carriers

Introduction

Hypodontia, hypohidrosis, sparse hair and characteristic faces are the main characters of X-linked hypohidrotic ectodermal dysplasia (XLHED) which is caused by genetic ectodysplasin A (EDA) deficiency. Heterozygous female carriers tend to have mild to moderate XLHED phenotype, even though 30% of them present no obvious symptom.

Methods

A large Chinese XLHED family was reported and the entire coding region and exon–intron boundaries of EDA gene were sequenced. To elucidate the mechanism for carriers’ tempered phenotype, we analyzed the methylation level on four sites of the promoter of EDA by the pyrosequencing system.

Results

A known frameshift mutation (c.573–574 insT) was found in this pedigree. Combined with the pedigrees we reported before, 120 samples comprised of 23 carrier females from 11 families and 97 healthy females were analyzed for the methylation state of EDA promoter. Within 95% confidence interval (CI), 18 (78.26%) carriers were hypermethylated at these 4 sites.

Conclusion

Chinese XLHED carriers often have a hypermethylated EDA promoter.

Non-syndromic Tooth Agenesis Associated with a Nonsense Mutation in Ectodysplasin-A (EDA)

Mutations in the ectodysplasin-A ( EDA) gene have been generally associated with X-linked hypohidrotic ectodermal dysplasia (XLHED). Recently, missense mutations in EDA have been reported to cause familial non-syndromic tooth agenesis. In this study, we report a novel EDA mutation in an Estonian family segregating non-syndromic tooth agenesis with variable expressivity. Affected individuals had no associated defects in other ectodermal organs. Using whole-exome sequencing, we identified a heterozygous nonsense mutation c.874G>T (p.Glu292X) in the TNF homology domain of EDA in all affected female patients. This protein-altering variant arose de novo, and the potentially causative allele was transmitted to affected offspring from the affected mother. We suggest that the dental phenotype variability described in heterozygous female carriers of EDA mutation may occur because of the differential pattern of X-chromosome inactivation, which retains reduced levels of EDA-receptor signaling in tissues involved in tooth morphogenesis. This results in selective tooth agenesis rather than XLHED phenotype. The present study broadens the mutation spectrum for this locus and demonstrates that EDA mutations may result in non-syndromic tooth agenesis in heterozygous females.

Historical perspectives on tumor necrosis factor and its superfamily: 25 years later, a golden journey

Although activity that induced tumor regression was observed and termed tumor necrosis factor (TNF) as early as the 1960s, the true identity of TNF was not clear until 1984, when Aggarwal and coworkers reported, for the first time, the isolation of 2 cytotoxic factors: one, derived from macrophages (molecular mass 17 kDa), was named TNF, and the second, derived from lymphocytes (20 kDa), was named lymphotoxin. Because the 2 cytotoxic factors exhibited 50% amino acid sequence homology and bound to the same receptor, they came to be called TNF-α and TNF-β. Identification of the protein sequences led to cloning of their cDNA. Based on sequence homology to TNF-α, now a total of 19 members of the TNF superfamily have been identified, along with 29 interacting receptors, and several molecules that interact with the cytoplasmic domain of these receptors. The roles of the TNF superfamily in inflammation, apoptosis, proliferation, invasion, angiogenesis, metastasis, and morphogenesis have been documented. Their roles in immunologic, cardiovascular, neurologic, pulmonary, and metabolic diseases are becoming apparent. TNF superfamily members are active targets for drug development, as indicated by the recent approval and expanding market of TNF blockers used to treat rheumatoid arthritis, psoriasis, Crohns disease, and osteoporosis, with a total market of more than US $20 billion. As we learn more about this family, more therapeutics will probably emerge. In this review, we summarize the initial discovery of TNF-α, and the insights gained regarding the roles of this molecule and its related family members in normal physiology and disease.

Hypohidrotic ectodermal dysplasia and immunodeficiency with coincident NEMO and EDA mutations

Ectodermal dysplasias (ED) are uncommon genetic disorders resulting in abnormalities in ectodermally derived structures. Many ED-associated genes have been described, of which ectodysplasin-A (EDA) is one of the more common. The NF-κB essential modulator (NEMO encoded by the IKBKG gene) is unique in that mutations result in severe humoral and cellular immunologic defects in addition to ED. We describe three unrelated kindreds with defects in both EDA and IKBKG resulting from X-chromosome crossover. This demonstrates the importance of thorough immunologic consideration of patients with ED even when an EDA etiology is confirmed, and raises the possibility of a specific phenotype arising from coincident mutations in EDA and IKBKG.

Inter-chromosomal variation in the pattern of human population genetic structure

Emerging technologies now make it possible to genotype hundreds of thousands of genetic variations in individuals, across the genome. The study of loci at finer scales will facilitate the understanding of genetic variation at genomic and geographic levels. We examined global and chromosomal variations across HapMap populations using 3.7 million single nucleotide polymorphisms to search for the most stratified genomic regions of human populations and linked these regions to ontological annotation and functional network analysis. To achieve this, we used five complementary statistical and genetic network procedures: principal component (PC), cluster, discriminant, fixation index (F_ST) and network/pathway analyses. At the global level, the first two PC scores were sufficient to account for major population structure; however, chromosomal level analysis detected subtle forms of population structure within continental populations, and as many as 31 PCs were required to classify individuals into homogeneous groups. Using recommended population ancestry differentiation measures, a total of 126 regions of the genome were catalogued. Gene ontology and networks analyses revealed that these regions included the genes encoding oculocutaneous albinism II (OCA2), hect domain and RLD 2 (HERC2), ectodysplasin A receptor (EDAR) and solute carrier family 45, member 2 (SLC45A2). These genes are associated with melanin production, which is involved in the development of skin and hair colour, skin cancer and eye pigmentation. We also identified the genes encoding interferon-γ (IFNG) and death-associated protein kinase 1 (DAPK1), which are associated with cell death, inflammatory and immunological diseases. An in-depth understanding of these genomic regions may help to explain variations in adaptation to different environments. Our approach offers a comprehensive strategy for analysing chromosome-based population structure and differentiation, and demonstrates the application of complementary statistical and functional network analysis in human genetic variation studies.

Ectodermal Dysplasia: A Case Report

Ectodermal dysplasia is a hereditary disease characterized by dysplasia of tissues of ectodermal origin. The incidence of ectodermal dysplasia is rare (1 in 100,000 birth). This case report discusses the features, classification and prosthetic treatment plan (upper partial denture and lower complete denture for upper partial and lower complete edentulous arches respectively). This treatment plan would be able to provide psychological and functional boost to the sufferer.

Molecular and therapeutic characterization of anti-ectodysplasin A receptor (EDAR) agonist monoclonal antibodies

The TNF family ligand ectodysplasin A (EDA) and its receptor EDAR are required for proper development of skin appendages such as hair, teeth, and eccrine sweat glands. Loss of function mutations in the Eda gene cause X-linked hypohidrotic ectodermal dysplasia (XLHED), a condition that can be ameliorated in mice and dogs by timely administration of recombinant EDA. In this study, several agonist anti-EDAR monoclonal antibodies were generated that cross-react with the extracellular domains of human, dog, rat, mouse, and chicken EDAR. Their half-life in adult mice was about 11 days. They induced tail hair and sweat gland formation when administered to newborn EDA-deficient Tabby mice, with an EC(50) of 0.1 to 0.7 mg/kg. Divalency was necessary and sufficient for this therapeutic activity. Only some antibodies were also agonists in an in vitro surrogate activity assay based on the activation of the apoptotic Fas pathway. Activity in this assay correlated with small dissociation constants. When administered in utero in mice or at birth in dogs, agonist antibodies reverted several ectodermal dysplasia features, including tooth morphology. These antibodies are therefore predicted to efficiently trigger EDAR signaling in many vertebrate species and will be particularly suited for long term treatments.

Isolated oligodontia associated with mutations in EDARADD, AXIN2, MSX1, and PAX9 genes

Oligodontia is defined as the congenital lack of six or more permanent teeth, excluding third molars. Oligodontia as well as hypodontia (lack of one or more permanent teeth) are highly heritable conditions associated with mutations in the AXIN2, MSX1, PAX9, EDA, and EDAR genes. Here we define the prevalence of mutations in the AXIN2, MSX1, PAX9, EDA, and EDAR genes, and the novel candidate gene EDARADD in a cohort of 93 Swedish probands with non-syndromic, isolated oligodontia. Mutation screening was performed using denaturing gradient gel electrophoresis and DNA sequence analysis. Analyses of the coding sequences of the six genes showed sequence alterations predicted to be damaging or potentially damaging in ten of 93 probands (10.8%). Mutations were identified in the EDARADD (n = 1), AXIN2 (n = 3), MSX1 (n = 2), and PAX9 (n = 4) genes, respectively. None of the 10 probands with mutations had other self-reported symptoms from ectodermal tissues. The oral parameters were similar when comparing individuals with and without mutations but a family history of oligodontia was three times more frequent for probands with mutations. EDARADD mutations have previously been reported in a few families segregating hypohidrotic ectodermal dysplasia and this is, to our knowledge, the first report of an EDARADD mutation associated with isolated oligodontia.

Subtle Morphological Changes in the Mandible of Tabby Mice Revealed by Micro-CT Imaging and Elliptical Fourier Quantification

X-linked hypohidrotic ectodermal dysplasia (XLHED) is a genetic disorder due to a mutation of the EDA gene and is mainly characterized by an impaired formation of hair, teeth and sweat glands, and craniofacial dysmorphologies. Although tooth abnormalities in Tabby (Ta) mutant mice - the murine model of XLHED - have been extensively studied, characterization of the craniofacial complex, and more specifically the mandibular morphology has received less attention. From 3D micro-CT reconstructions of the left mandible, the mandibular outline observed in lateral view, was quantified using 2D elliptical Fourier analysis. Comparisons between Ta specimens and their wild-type controls were carried out showing significant shape differences between mouse strains enabling a clear distinction between hemizygous Ta specimens and the other mouse groups (WT and heterozygous Eda(Ta/+) specimens). Morphological differences associated with HED correspond not only to global mandibular features (restrained development of that bone along dorsoventral axis), but also to subtle aspects such as the marked backward projection of the coronoid process or the narrowing of the mandibular condylar neck. These modifications provide for the first time, evidence of a predominant effect of the Ta mutation on the mandibular morphology. These findings parallel the well described abnormalities of jugal tooth row and skeletal defects in Ta mice, and underline the role played by EDA-A in the reciprocal epithelial-mesenchymal interactions that are of critical importance in normal dental and craniofacial development.

Correlation between the phenotypes and genotypes of X-linked hypohidrotic ectodermal dysplasia and non-syndromic hypodontia caused by ectodysplasin-A mutations

Mutations in the ectodysplasin-A (EDA) gene can cause both X-linked hypohidrotic ectodermal dysplasia (XLHED) and non-syndromic hypodontia (NSH). The correlation between the phenotypes and genotypes of these two conditions has yet to be described. In the present study, 27 non-consanguineous Chinese XLHED subjects were screened and 17 EDA mutations were identified. In order to investigate the correlation between genotype and phenotype, we also reviewed related studies on NSH subjects with confirmed EDA mutations and compared the differences in the clinical manifestations and EDA mutations of the two conditions. Tooth agenesis was observed in addition to abnormalities of other ectodermal organs. Tooth agenesis was more severe in XLHED subjects than in NSH subjects, and there were statistically significant differences in 10 tooth positions in the XLHED and NSH subjects, including canines, premolars, and molars. With the exception of one splicing mutation, all mutations in the NSH subjects were missense mutations, and these were most likely to be located in the tumor necrosis factor (TNF) domain. Further, more than half of the mutations in the XLHED subjects were speculated to be loss of function mutations, such as nonsense, insertion, and deletion mutations, and these mutations were distributed across all EDA domains. Our results show that there exists a correlation between the phenotypes and genotypes of XLHED and NSH subjects harboring EDA mutations. Further, our findings suggest that NSH is probably a variable expression of XLHED. This finding might be useful for clinical diagnosis and genetic counseling in clinical practice, and provides some insight into the different manifestations of EDA mutations in different ectodermal organs.

A novel mutation of the bovine EDA gene associated with anhidrotic ectodermal dysplasia in Holstein cattle

Anhidrotic ectodermal dysplasia (EDA) is a genetic disease characterized by the absence or hypoplasia of hair, teeth and eccrine sweat glands that has been reported in humans, the tabby mouse mutants, cattle and dogs. The EDA gene on the X chromosome encodes a protein, ectodysplasin-A (EDA), which is responsible for EDA. Here we describe a novel mutation of the EDA gene in which a 19 bp deletion in exon 1 in male Holstein calves demonstrated the phenotypic features of EDA. The dam and the grand-dam of the affected calves were heterozygous for this deletion. It is assumed that this deletion close to the start codon confuses all transcripts, and leads to the complete loss of pleiotropic functions of the bovine EDA gene. These results suggest that this mutation might be useful as animal models for the investigation of the pathogenic mechanisms of the anhidrotic ectodermal dysplasia.

Missense mutation of the EDA gene in a Jordanian family with X-linked hypohidrotic ectodermal dysplasia: phenotypic appearance and speech problems

Mutations in the EDA gene are responsible for X-linked hypohidrotic ectodermal dysplasia, the most common form of ectodermal dysplasia. Males show a severe form of this disease, while females often manifest mild to moderate symptoms. We identified a missense mutation (c.463C>T) in the EDA gene in a Jordanian family, using direct DNA sequencing. This mutation leads to an amino acid change of arginine to cysteine in the extracellular domain of ectodysplasin-A, a protein encoded by the EDA gene. The phenotype of a severely affected 11-year-old boy with this mutation included heat intolerance, sparse hair (hypotrichosis), absence of 17 teeth (oligodontia), speech problems, and damaged eccrine glands, resulting in reduced sweating (anhidrosis). Both the mother (40 years old) and the sister (10 years old) were carriers with mild to moderate symptoms of this disease, while the father was healthy. This detailed description of the phenotype caused by this missense mutation could be useful for prenatal diagnosis.

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.

From ectodermal dysplasia to selective tooth agenesis

The history and the lessons learned from hypohidrotic ectodermal dysplasia (HED) may serve as an example for the unraveling of the cause and pathogenesis of other ectodermal dysplasia syndromes by demonstrating that phenotypically identical syndromes (HED) can be caused by mutations in different genes (EDA, EDAR, EDARADD), that mutations in the same gene (EDA) can lead to different phenotypes (HED and selective tooth agenesis) and that mutations in genes further downstream in the same signaling pathway (NEMO) may modify the phenotype quite profoundly (incontinentia pigmenti (IP) and HED with immunodeficiency). But it also demonstrates that diligent phenotype characterization and classification is extremely helpful in uncovering the underlying genotype. We also present a new mutation in the EDA gene which causes selective tooth agenesis and demonstrates the phenotype variation that can be encountered in the ectodermal dysplasia syndrome (HED) with the highest prevalence worldwide.

Functional analysis of Ectodysplasin-A mutations causing selective tooth agenesis

Mutations of the Ectodysplasin-A (EDA) gene are generally associated with the syndrome hypohidrotic ectodermal dysplasia (MIM 305100), but they can also manifest as selective, non-syndromic tooth agenesis (MIM300606). We have performed an in vitro functional analysis of six selective tooth agenesis-causing EDA mutations (one novel and five known) that are located in the C-terminal tumor necrosis factor homology domain of the protein. Our study reveals that expression, receptor binding or signaling capability of the mutant EDA1 proteins is only impaired in contrast to syndrome-causing mutations, which we have previously shown to abolish EDA1 expression, receptor binding or signaling. Our results support a model in which the development of the human dentition, especially of anterior teeth, requires the highest level of EDA-receptor signaling, whereas other ectodermal appendages, including posterior teeth, have less stringent requirements and form normally in response to EDA mutations with reduced activity.

Genomic and geographic distribution of private SNPs and pathways in human populations

AIMS: Geography-based genetic differentials operating on entire biochemical pathways may reflect different adaptive evolutionary processes that separated populations may have undergone. They may also influence treatment outcome for a variety of drugs - an emerging and important area of study. This research article leverages the International HapMap Consortium data to identify pathway components that differ in genotype frequency for four populations: individuals of Northern European descent from the USA (CEU), individuals from West Africa (YRI), Japan (JPT) and China (CHB). MATERIALS #ENTITYSTARTX00026; METHODS: By identifying loci with fixed or large frequency differences (δ = 1) between paired population samples (CEU vs YRI, CEU vs CHB, CEU vs JPT, YRI vs CHB, YRI vs JPT and CHB vs JPT), and reconstructing the physiological functions of genes at these loci, we report a list of pathways affected by natural selection during human evolution. RESULTS: Of the 3.7 million HapMap SNPs, 463 loci (which mapped to 38 genes) were fixed (δ = 1) in at least one population pair. These private loci included four nonsynonymous coding SNPs: rs4536103 (NEUROG3), rs1385699 (EDA2R), rs11946338 (ARHGAP24) and rs4422842 (CACNA1B). A total of four additional genes demonstrated evidence of recent positive selection: three genes in European subjects (IER5L, NPNT and SESTD1) and a single gene in Asian subjects (EXOC6B). DISCUSSION: Gene ontology and pathway analyses suggest that cellular differentiation, apoptosis and activation of the NF-κB transcription factor vary between populations in genomic regions of fixed (private) SNPs identified in this study. Variability in these pathways may provide important clues into the mechanisms of human adaptation to different environments. An improved understanding of their variability may also help to explain race-specific differences in the treatment outcomes observed for a variety of modern drugs.

Growth hormone neurosecretory dysfunction in a boy with hypohidrotic/anhidrotic ectodermal dysplasia: definition of short stature, molecular characterization and long-term hGH replacement treatment to final height

Anhidrotic/hypohidrotic ectodermal dysplasia is a rare disorder, genetically heterogeneous, commonly X-linked recessive inherited, characterized by hypoplasia up to the absence of the eccrine glands with hypo-anhidrosis and secondary hyperpyrexia, hypodontia and some typical craniofacial features. Some papers have described how these patients may show poor growth, while other recent research shows normal growth. We report a boy with anhidrotic/hypohidrotic ectodermal dysplasia and growth hormone neurosecretory dysfunction, an association not previously reported, and we discuss the possible causes as well as the patient's response to growth hormone treatment until he reached final height.

Biological activity of ectodysplasin A is conditioned by its collagen and heparan sulfate proteoglycan-binding domains

Mutations in the TNF family ligand EDA1 cause X-linked hypohidrotic ectodermal dysplasia (XLHED), a condition characterized by defective development of skin appendages. The EDA1 protein displays a proteolytic processing site responsible for its conversion to a soluble form, a collagen domain, and a trimeric TNF homology domain (THD) that binds the receptor EDAR. In-frame deletions in the collagen domain reduced the thermal stability of EDA1. Removal of the collagen domain decreased its activity about 100-fold, as measured with natural and engineered EDA1-responsive cell lines. The collagen domain could be functionally replaced by multimerization domains or by cross-linking antibodies, suggesting that it functions as an oligomerization unit. Surprisingly, mature soluble EDA1 containing the collagen domain was poorly active when administered in newborn, EDA-deficient (Tabby) mice. This was due to a short stretch of basic amino acids located at the N terminus of the collagen domain that confers EDA1 with proteoglycan binding ability. In contrast to wild-type EDA1, EDA1 with mutations in this basic sequence was a potent inducer of tail hair development in vivo. Thus, the collagen domain activates EDA1 by multimerization, whereas the proteoglycan-binding domain may restrict the distribution of endogeneous EDA1 in vivo.

Two novel mutations in the ED1 gene in Japanese families with X-linked hypohidrotic ectodermal dysplasia

X-linked hypohidrotic ectodermal dysplasia (XLHED), which is characterized by hypodontia, hypotrichosis, and hypohidrosis, is caused by mutations in ED1, the gene encoding ectodysplasin-A (EDA). This protein belongs to the tumor necrosis factor ligand superfamily. We analyzed ED1 in two Japanese patients with XLHED. In patient 1, we identified a 4-nucleotide insertion, c.119-120insTGTG, in exon 1, which led to a frameshift mutation starting from that point (p.L40fsX100). The patient's mother was heterozygous for this mutation. In patient 2, we identified a novel missense mutation, c.1141G>C, in exon 9, which led to a substitution of glycine with arginine in the TNFL domain of EDA (p.G381R). This patient's mother and siblings showed neither symptoms nor ED1 mutations, so this mutation was believed to be a de novo mutation in maternal germline cells. According to molecular simulation analysis of protein structure and electrostatic surface, p.G381R increases the distance between K375 in monomer A and K327 in monomer B, which suggests an alteration of overall structure of EDA. Thus, we identified two novel mutations, p.L40fsX100 and p.G381R, in ED1 of two XLHED patients. Simulation analysis suggested that the p.G381R mutation hampers binding of EDA to its receptor via alteration of overall EDA structure.

[Anhidrotic ectodermal dysplasia. Report of a rare mutation in EDA1]

BACKGROUND

Anhidrotic ectodermal dysplasia is a rare inherited disorder seen mainly in the X-linked recessive form. We report the case of a Lebanese family in which the mother transmitted an uncommon missense mutation to three of her sons.

PATIENTS AND METHODS

A 23-year-old patient presented with keloids in nodular acne. The physical examination showed fine and sparse hair, thick everted lips and dental defects. A detailed history revealed congenital anhidrosis. The patient's, seven-year-old and four-year-old brothers had the same characteristic facial morphology and were also presenting anhidrosis. The mother had hypodontia. The parents, though not consanguineous, were from the same village. Genetic testing with sequencing of the EDA1 gene revealed a missense mutation affecting codon 155.

DISCUSSION

Ectodermal dysplasias are currently found in more than 150 syndromes. The patient's history and the clinical signs suggest the X-linked recessive form of anhidrotic ectodermal dysplasia due to a mutation in EDA1 gene encoding the ectodysplasin. The mutation found in this family is very rare and was mentioned once in a study on splicing forms that permit detection of all EDA1 mutations. Besides, this patient tolerated oral isotretinoin perfectly well, unlike another case reported once in the literature. Finally, genetic counselors must inform carrier mothers of the high recurrence rate among male offspring.

Dento-craniofacial phenotypes and underlying molecular mechanisms in hypohidrotic ectodermal dysplasia (HED): a review

The hypohidrotic ectodermal dysplasias (HED) belong to a large and heterogeneous nosological group of polymalfomative syndromes characterized by dystrophy or agenesis of ectodermal derivatives. Molecular etiologies of HED consist of mutations of the genes involved in the Ectodysplasin (EDA)-NF-kappaB pathway. Besides the classic ectodermal signs, craniofacial and bone manifestations are associated with the phenotypic spectrum of HED. The dental phenotype of HED consists of various degrees of oligodontia with other dental abnormalities, and these are important in the early diagnosis and identification of persons with HED. Phenotypic dental markers of heterozygous females for EDA gene mutation-moderate oligodontia, conical incisors, and delayed dental eruption-are important for individuals giving reliable genetic counseling. Some dental ageneses observed in HED are also encountered in non-syndromic oligodontia. These clinical similarities may reflect possible interactions between homeobox genes implicated in early steps of odontogenesis and the Ectodysplasin (EDA)-NF-kappaB pathway. Craniofacial dysmorphologies and bone structural anomalies are also associated with the phenotypic spectrum of persons with HED patients. The corresponding molecular mechanisms involve altered interactions between the EDA-NF-kappaB pathway and signaling molecules essential in skeletogenic neural crest cell differentiation, migration, and osteoclastic differentiation. Regarding oral treatment of persons with HED, implant-supported prostheses are used with a relatively high implant survival rate. Recently, groundbreaking experimental approaches with recombinant EDA or transgenesis of EDA-A1 were developed from the perspective of systemic treatment and appear very promising. All these clinical observations and molecular data allow for the specification of the craniofacial phenotypic spectrum in HED and provide a better understanding of the mechanisms involved in the pathogenesis of this syndrome.

Non-syndromic tooth agenesis in two Chinese families associated with novel missense mutations in the TNF domain of EDA (ectodysplasin A)

Here we report two unrelated Chinese families with congenital missing teeth inherited in an X-linked manner. We mapped the affected locus to chromosome Xp11-Xq21 in one family. In the defined region, both families were found to have novel missense mutations in the ectodysplasin-A (EDA) gene. The mutation of c.947A>G caused the D316G substitution of the EDA protein. The mutation of c.1013C>T found in the other family resulted in the Thr to Met mutation at position 338 of EDA. The EDA gene has been reported responsible for X-linked hypohidrotic ectodermal dysplasia (XLHED) in humans characterized by impaired development of hair, eccrine sweat glands, and teeth. In contrast, all the affected individuals in the two families that we studied here had normal hair and skin. Structural analysis suggests that these two novel mutants may account for the milder phenotype by affecting the stability of EDA trimers. Our results indicate that these novel missense mutations in EDA are associated with the isolated tooth agenesis and provide preliminary explanation for the abnormal clinical phenotype at a molecular structural level.

X-linked hypohidrotic ectodermal dysplasia. Genetic and dental findings in 67 Danish patients from 19 families

This study aimed to investigate genotype and phenotype in males affected with X-linked hypohidrotic ectodermal dysplasia (HED) and in female carriers, to analyse a possible genotype-phenotype correlation, and to analyse a possible relation between severity of the symptoms and the X-chromosome inactivation pattern in female carriers. The study group comprised 67 patients from 19 families (24 affected males and 43 female carriers). All participants had clinical signs of ectodermal dysplasia and a disease-causing EDA mutation. The EDA gene was screened for mutations by single-stranded conformational polymorphism and direct sequencing. Multiplex ligation-dependent probe amplification (MLPA) analysis was used to detect deletions/duplications in female probands. Sixteen different EDA mutations were detected in the 19 families, nine not described previously. The MLPA analysis detected a deletion of exon 1 in one female proband. No genotype-phenotype correlations were observed, and female carriers did not exhibit a skewed X-chromosome inactivation pattern. However, in two female carriers with pronounced clinical symptoms, in whom the parental origin of each allele was known, we observed that mainly the normal allele was inactivated.