Heterozygous mutation in the SAM domain of p63 underlies Rapp-Hodgkin ectodermal dysplasia

Amelogenesis imperfecta: Next-generation sequencing sheds light on Witkop's classification

Amelogenesis imperfecta (AI) is a heterogeneous group of genetic rare diseases disrupting enamel development (Smith et al., Front Physiol, 2017a, 8, 333). The clinical enamel phenotypes can be described as hypoplastic, hypomineralized or hypomature and serve as a basis, together with the mode of inheritance, to Witkop's classification (Witkop, J Oral Pathol, 1988, 17, 547-553). AI can be described in isolation or associated with others symptoms in syndromes. Its occurrence was estimated to range from 1/700 to 1/14,000. More than 70 genes have currently been identified as causative. Objectives: We analyzed using next-generation sequencing (NGS) a heterogeneous cohort of AI patients in order to determine the molecular etiology of AI and to improve diagnosis and disease management. Methods: Individuals presenting with so called "isolated" or syndromic AI were enrolled and examined at the Reference Centre for Rare Oral and Dental Diseases (O-Rares) using D4/phenodent protocol (www.phenodent.org). Families gave written informed consents for both phenotyping and molecular analysis and diagnosis using a dedicated NGS panel named GenoDENT. This panel explores currently simultaneously 567 genes. The study is registered under NCT01746121 and NCT02397824 (https://clinicaltrials.gov/). Results: GenoDENT obtained a 60% diagnostic rate. We reported genetics results for 221 persons divided between 115 AI index cases and their 106 associated relatives from a total of 111 families. From this index cohort, 73% were diagnosed with non-syndromic amelogenesis imperfecta and 27% with syndromic amelogenesis imperfecta. Each individual was classified according to the AI phenotype. Type I hypoplastic AI represented 61 individuals (53%), Type II hypomature AI affected 31 individuals (27%), Type III hypomineralized AI was diagnosed in 18 individuals (16%) and Type IV hypoplastic-hypomature AI with taurodontism concerned 5 individuals (4%). We validated the genetic diagnosis, with class 4 (likely pathogenic) or class 5 (pathogenic) variants, for 81% of the cohort, and identified candidate variants (variant of uncertain significance or VUS) for 19% of index cases. Among the 151 sequenced variants, 47 are newly reported and classified as class 4 or 5. The most frequently discovered genotypes were associated with MMP20 and FAM83H for isolated AI. FAM20A and LTBP3 genes were the most frequent genes identified for syndromic AI. Patients negative to the panel were resolved with exome sequencing elucidating for example the gene involved ie ACP4 or digenic inheritance. Conclusion: NGS GenoDENT panel is a validated and cost-efficient technique offering new perspectives to understand underlying molecular mechanisms of AI. Discovering variants in genes involved in syndromic AI (CNNM4, WDR72, FAM20A … ) transformed patient overall care. Unravelling the genetic basis of AI sheds light on Witkop's AI classification.

Genetics and signaling mechanisms of orofacial clefts

Craniofacial development involves several complex tissue movements including several fusion processes to form the frontonasal and maxillary structures, including the upper lip and palate. Each of these movements are controlled by many different factors that are tightly regulated by several integral morphogenetic signaling pathways. Subject to both genetic and environmental influences, interruption at nearly any stage can disrupt lip, nasal, or palate fusion and result in a cleft. Here, we discuss many of the genetic risk factors that may contribute to the presentation of orofacial clefts in patients, and several of the key signaling pathways and underlying cellular mechanisms that control lip and palate formation, as identified primarily through investigating equivalent processes in animal models, are examined.

Genome-wide meta-analyses of nonsyndromic orofacial clefts identify novel associations between FOXE1 and all orofacial clefts, and TP63 and cleft lip with or without cleft palate

Nonsyndromic orofacial clefts (OFCs) are a heterogeneous group of common craniofacial birth defects with complex etiologies that include genetic and environmental risk factors. OFCs are commonly categorized as cleft lip with or without cleft palate (CL/P) and cleft palate alone (CP), which have historically been analyzed as distinct entities. Genes for both CL/P and CP have been identified via multiple genome-wide linkage and association studies (GWAS); however, altogether, known variants account for a minority of the estimated heritability in risk to these craniofacial birth defects. We performed genome-wide meta-analyses of CL/P, CP, and all OFCs across two large, multiethnic studies. We then performed population-specific meta-analyses in sub-samples of Asian and European ancestry. In addition to observing associations with known variants, we identified a novel genome-wide significant association between SNPs located in an intronic TP63 enhancer and CL/P (p = 1.16 × 10-8). Several novel loci with compelling candidate genes approached genome-wide significance on 4q21.1 (SHROOM3), 12q13.13 (KRT18), and 8p21 (NRG1). In the analysis of all OFCs combined, SNPs near FOXE1 reached genome-wide significance (p = 1.33 × 10-9). Our results support the highly heterogeneous nature of OFCs and illustrate the utility of meta-analysis for discovering new genetic risk factors.

p63 threonine phosphorylation signals the interaction with the WW domain of the E3 ligase Itch

Both in epithelial development as well as in epithelial cancers, the p53 family member p63 plays a crucial role acting as a master transcriptional regulator. P63 steady state protein levels are regulated by the E3 ubiquitin ligase Itch, via a physical interaction between the PPxY consensus sequence (PY motif) of p63 and one of the 4 WW domains of Itch; this substrate recognition process leads to protein-ubiquitylation and p63 proteasomal degradation. The interaction of the WW domains, a highly compact protein-protein binding module, with the short proline-rich sequences is therefore a crucial regulatory event that may offer innovative potential therapeutic opportunity. Previous molecular studies on the Itch-p63 recognition have been performed in vitro using the Itch-WW2 domain and the peptide interacting fragment of p63 (pep63), which includes the PY motif. Itch-WW2-pep63 interaction is also stabilized in vitro by the conformational constriction of the S-S cyclization in the p63 peptide. The PY motif of p63, as also for other proteins, is characterized by the nearby presence of a (T/S)P motif, which is a potential recognition site of the WW domain of the IV group present in the prolyl-isomerase Pin1. In this study, we demonstrate, by in silico and spectroscopical studies using both the linear pep63 and its cyclic form, that the threonine phosphorylation of the (T/S)PPPxY motif may represent a crucial regulatory event of the Itch-mediated p63 ubiquitylation, increasing the Itch-WW domains-p63 recognition event and stabilizing in vivo the Itch-WW-p63 complex. Moreover, our studies confirm that the subsequently trans/cis proline isomerization of (T/S)P motif by the Pin1 prolyl-isomerase, could modulate the E3-ligase interaction, and that the (T/S)pPtransPPxY motif represent the best conformer for the ItchWW-(T/S)PPPxY motif recognition.

Large cryptic genomic rearrangements with apparently normal karyotypes detected by array-CGH

Background

Conventional karyotyping (550 bands resolution) is able to identify chromosomal aberrations >5-10 Mb, which represent a known cause of intellectual disability/developmental delay (ID/DD) and/or multiple congenital anomalies (MCA). Array-Comparative Genomic Hybridization (array-CGH) has increased the diagnostic yield of 15-20%.

Results

In a cohort of 700 ID/DD cases with or without MCA, including 15 prenatal diagnoses, we identified a subgroup of seven patients with a normal karyotype and a large complex rearrangement detected by array-CGH (at least 6, and up to 18 Mb). FISH analysis could be performed on six cases and showed that rearrangements were translocation derivatives, indistinguishable from a normal karyotype as they involved a similar band pattern and size. Five were inherited from a parent with a balanced translocation, whereas two were apparently de novo. Genes spanning the rearrangements could be associated with some phenotypic features in three cases (case 3: DOCK8; case 4: GATA3, AKR1C4; case 6: AS/PWS deletion, CHRNA7), and in two, likely disease genes were present (case 5: NR2F2, TP63, IGF1R; case 7: CDON). Three of our cases were prenatal diagnoses with an apparently normal karyotype.

Conclusions

Large complex rearrangements of up to 18 Mb, involving chromosomal regions with similar size and band appearance may be overlooked by conventional karyotyping. Array-CGH allows a precise chromosomal diagnosis and recurrence risk definition, further confirming this analysis as a first tier approach to clarify molecular bases of ID/DD and/or MCA. In prenatal tests, array-CGH is confirmed as an important tool to avoid false negative results due to karyotype intrinsic limit of detection.

Modeling AEC-New approaches to study rare genetic disorders

Ankyloblepharon-ectodermal defects-cleft lip/palate (AEC) syndrome is a rare monogenetic disorder that is characterized by severe abnormalities in ectoderm-derived tissues, such as skin and its appendages. A major cause of morbidity among affected infants is severe and chronic skin erosions. Currently, supportive care is the only available treatment option for AEC patients. Mutations in TP63, a gene that encodes key regulators of epidermal development, are the genetic cause of AEC. However, it is currently not clear how mutations in TP63 lead to the various defects seen in the patients' skin. In this review, we will discuss current knowledge of the AEC disease mechanism obtained by studying patient tissue and genetically engineered mouse models designed to mimic aspects of the disorder. We will then focus on new approaches to model AEC, including the use of patient cells and stem cell technology to replicate the disease in a human tissue culture model. The latter approach will advance our understanding of the disease and will allow for the development of new in vitro systems to identify drugs for the treatment of skin erosions in AEC patients. Further, the use of stem cell technology, in particular induced pluripotent stem cells (iPSC), will enable researchers to develop new therapeutic approaches to treat the disease using the patient's own cells (autologous keratinocyte transplantation) after correction of the disease-causing mutations.

To grow or not to grow: hair morphogenesis and human genetic hair disorders

Mouse models have greatly helped in elucidating the molecular mechanisms involved in hair formation and regeneration. Recent publications have reviewed the genes involved in mouse hair development based on the phenotype of transgenic, knockout and mutant animal models. While much of this information has been instrumental in determining molecular aspects of human hair development and cycling, mice exhibit a specific pattern of hair morphogenesis and hair distribution throughout the body that cannot be directly correlated to human hair. In this mini-review, we discuss specific aspects of human hair follicle development and present an up-to-date summary of human genetic disorders associated with abnormalities in hair follicle morphogenesis, structure or regeneration.

Clinical, genetic, and molecular aspects of split-hand/foot malformation: an update

We here provide an update on the clinical, genetic, and molecular aspects of split-hand/foot malformation (SHFM). This rare condition, affecting 1 in 8,500-25,000 newborns, is extremely complex because of its variability in clinical presentation, irregularities in its inheritance pattern, and the heterogeneity of molecular genetic alterations that can be found in affected individuals. Both syndromal and nonsyndromal forms are reviewed and the major molecular genetic alterations thus far reported in association with SHFM are discussed. This updated overview should be helpful for clinicians in their efforts to make an appropriate clinical and genetic diagnosis, provide an accurate recurrence risk assessment, and formulate a management plan.

Gene p63: In ectrodactyly-ectodermal dysplasia clefting, ankyloblepharon-ectodermal dysplasia, Rapp-Hodgkin syndrome

INTRODUCTION

An analysis was made of three different syndromes associated with p63 gene mutations, known as ectrodactyly-ectodermal dysplasia-clefting syndrome (EEC), ankyloblepharon-ectodermal dysplasia clefting syndrome (AEC or Hay-Wells) and Rapp-Hodgkin syndrome (RHS). The postoperative complications associated with their cleft reconstructions were also evaluated.

MATERIALS AND METHODS

Extensive demographic information, in particular of the clinical appearances, associated malformations, and the types and complications of the reconstructive surgical procedures, were recorded of these syndromic cases occurring in a database of 3621 facial cleft deformity patients. The data was analyzed using the Microsoft Excel program.

RESULTS

A total of 10 (0.28%) cases of p63 associated syndromes were recorded: EEC (6), RHS (3), and AEC (1). The following clinical cleft appearances were noted - EEC = 6: CLA 1 -right side unilateral (female); CLAP 4 - right side (1) + left side (1) unilateral (male + female); bilateral (2) (males); hPsP 1 (female) (divided in 3 Black, 2 White, 1 Indian); RHS = 3: CLAP 2 (White males); hPsP 1 (White female); AEC = 1: CLAP bilateral (White male). Other features of the syndromes were: skin, hand, foot, tooth, hair and nail involvement, and light sensitivity. Postoperative complications included: (i) stenosis of nasal opening, especially after reconstruction of the bilateral cleft lip and the columella lengthening (2 cases), (ii) premaxilla-prolabium fusion (2 cases), (iii) repeated occurrence of oro-nasal fistula in the hard palate (4 cases), and (iv) dysgnathial development of midfacial structures (3 cases).

DISCUSSION

Three different p63 associated syndromes (EEC, AEC, and RHS) were diagnosed (0.27% of the total facial cleft deformities database). The majority of the cases presented with a bilateral CLAP in males only. A number of females and males had unilateral CLA. The hPsP-cleft was recorded in females only. The associated ectodermal component most probably had a profoundly negative influence on postoperatively wound healing, which was observed in particular at the nasal openings, the premaxilla sulcus and in the hard palate mucosa. The reconstruction of p63 associated syndromes is a greater challenge than the usual cleft reconstruction to the surgeon.

Molecular diagnosis of genodermatoses

The progress of molecular genetics helps clinicians to prove or exclude a suspected diagnosis for a vast and yet increasing number of genodermatoses. This leads to precise genetic counselling, prenatal diagnosis and preimplantation genetic haplotyping for many inherited skin conditions. It is also helpful in such occasions as phenocopy, late onset and incomplete penetrance, uniparental disomy, mitochondrial inheritance and pigmentary mosaicism. Molecular methods of two genodermatoses are explained in detail, i.e. genodermatoses with skin fragility and neurofibromatosis type 1.

Genomic profiling of a human organotypic model of AEC syndrome reveals ZNF750 as an essential downstream target of mutant TP63

The basis for impaired differentiation in TP63 mutant ankyloblepharon-ectodermal dysplasia-clefting (AEC) syndrome is unknown. Human epidermis harboring AEC TP63 mutants recapitulated this impairment, along with downregulation of differentiation activators, including HOPX, GRHL3, KLF4, PRDM1, and ZNF750. Gene-set enrichment analysis indicated that disrupted expression of epidermal differentiation programs under the control of ZNF750 and KLF4 accounted for the majority of disrupted epidermal differentiation resulting from AEC mutant TP63. Chromatin immunoprecipitation (ChIP) analysis and ChIP-sequencing of TP63 binding in differentiated keratinocytes revealed ZNF750 as a direct target of wild-type and AEC mutant TP63. Restoring ZNF750 to AEC model tissue rescued activator expression and differentiation, indicating that AEC TP63-mediated ZNF750 inhibition contributes to differentiation defects in AEC. Incorporating disease-causing mutants into regenerated human tissue can thus dissect pathomechanisms and identify targets that reverse disease features.

Mutations in AEC syndrome skin reveal a role for p63 in basement membrane adhesion, skin barrier integrity and hair follicle biology

BACKGROUND

AEC (ankyloblepharon-ectodermal defects-clefting) syndrome is an autosomal dominant ectodermal dysplasia disorder caused by mutations in the transcription factor p63. Clinically, the skin is dry and often fragile; other features can include partial eyelid fusion (ankyloblepharon), hypodontia, orofacial clefting, sparse hair or alopecia, and nail dystrophy.

OBJECTIVES

To investigate how p63 gene mutations affect gene and protein expression in AEC syndrome skin.

METHODS

We performed microarray analysis on samples of intact and eroded AEC syndrome skin compared with control skin. Changes were verified by quantitative real-time reverse transcription-polymerase chain reaction and, for basal keratinocyte-associated genes, by immunohistochemistry and analysis of microdissected skin.

RESULTS

We identified significant upregulation of six genes and downregulation of 69 genes in AEC syndrome skin, with the main changes in genes implicated in epidermal adhesion, skin barrier formation and hair follicle biology. There was reduced expression of genes encoding the basement membrane proteins FRAS1 and collagen VII, as well as the skin barrier-associated small proline-rich proteins 1A and 4, late cornified envelope protein 5A, hornerin, and lipid transporters including ALOX15B. Reduced expression of the hair-associated keratins 25, 27, 31, 33B, 34, 35, 81 and 85 was also noted. We also confirmed similar alterations in gene expression for 26 of the 75 genes in eroded AEC scalp skin.

CONCLUSIONS

This study identifies specific changes in skin structural biology and signalling pathways that result from mutant p63 and provides new molecular insight into the AEC syndrome phenotype.

Human cataract mutations in EPHA2 SAM domain alter receptor stability and function

The cellular and molecular mechanisms underlying the pathogenesis of cataracts leading to visual impairment remain poorly understood. In recent studies, several mutations in the cytoplasmic sterile-α-motif (SAM) domain of human EPHA2 on chromosome 1p36 have been associated with hereditary cataracts in several families. Here, we have investigated how these SAM domain mutations affect EPHA2 activity. We showed that the SAM domain mutations dramatically destabilized the EPHA2 protein in a proteasome-dependent pathway, as evidenced by the increase of EPHA2 receptor levels in the presence of the proteasome inhibitor MG132. In addition, the expression of wild-type EPHA2 promoted the migration of the mouse lens epithelial αTN4-1 cells in the absence of ligand stimulation, whereas the mutants exhibited significantly reduced activity. In contrast, stimulation of EPHA2 with its ligand ephrin-A5 eradicates the enhancement of cell migration accompanied by Akt activation. Taken together, our studies suggest that the SAM domain of the EPHA2 protein plays critical roles in enhancing the stability of EPHA2 by modulating the proteasome-dependent process. Furthermore, activation of Akt switches EPHA2 from promoting to inhibiting cell migration upon ephrin-A5 binding. Our results provide the first report of multiple EPHA2 cataract mutations contributing to the destabilization of the receptor and causing the loss of cell migration activity.

Functional characterization of a novel TP63 mutation in a family with overlapping features of Rapp-Hodgkin/AEC/ADULT syndromes

Heterozygous mutations in TP63 cause a wide spectrum of autosomal dominant developmental disorders variably affecting skin, limbs, and face. TP63 encodes p63, a protein expressed in two main isoforms (Tap63 and ΔNp63) with critical roles in both cell differentiation and development. Some analyses suggest a relationship of the mutation site to the observed clinical picture, although this link is inconsistent. This suggests an appreciable phenotypic continuity within the TP63-related disorders. We report a 3-month-old boy ascertained for congenital scalp erosion and mild features of ectodermal dysplasia. His mother showed full-blown characteristics of Rapp-Hodgkin syndrome plus intense abdominal and popliteal freckling. Molecular investigation identified the novel TP63 mutation c.1697delG. We used a luciferase reporter assay to compare the effects on the p63 transactivation (TA) activity of c.1697delG with that of the p.Arg280Cys and p.Gln634X mutations, associated with ectrodactyly-ectodermal dysplasia-cleft lip/palate syndrome and isolated split hand/foot malformation, respectively. These results demonstrated complex behavior of c.1697delG in the TA of genes involved in epidermal differentiation and development and shed further light in the physiopathology of TP63-related disorders. © 2011 Wiley Periodicals, Inc.

Split hand-split foot-ectodermal dysplasia and amelogenesis imperfecta with a TP63 mutation

We report on a mother and son who were affected with split hand-split foot (formerly described as ectrodactyly), ectodermal dysplasia, hyperpigmentation of skin, and dystrophic nails. Their hair was wiry, brownish, and slow-growing. Scanning electron micrography of their scalp hair showed hypoplastic hair bulbs, partial loss of hair cuticles, and frayed hair shafts. The son was affected with amelogenesis Imperfecta (hypocalcification, hypoplasia, and hypomaturation types), in the primary and permanent dentition. An unerupted supernumerary maxillary second premolar and fusion of mandibular incisors were observed in the primary dentition and their permanent successors. Mutation analysis showed a c.588-2A > C mutation in TP63 in the mother and her son. It is predicted that an alternative splice site was used, specifically the AG located just three nucleotides upstream. Use of this site is predicted to include three extra nucleotides in the transcript and thus incorporation of a single extra amino acid (p.Thr195_Tyr196insPro). This is the first time that amelogenesis imperfecta, fusion of teeth, and a supernumerary premolar have been shown to be associated with a TP63 mutation.

p63, a story of mice and men

The transcription factor p63 is essential for the formation of the epidermis and other stratifying epithelia. This is clearly demonstrated by the severe abnormality of p63-deficient mice and by the development of certain types of ectodermal dysplasias in humans as a result of p63 mutations. Investigation of the in vivo functions of p63 is complicated by the occurrence of 10 different splicing isoforms and by its interaction with the other family members, p53 and p73. In vitro and in vivo models have been used to unravel the functions of p63 and its different isoforms, but the results or their interpretation are often contradictory. This review focuses on what mammalian in vivo models and patient studies have taught us in the last 10 years.

TP63 gene mutations in Chinese P63 syndrome patients

TP63 plays an essential role in the development of epidermis and skin appendages. Mutations in TP63 can give rise to a series of syndromes characterized by various combinations of ectodermal dysplasia, limb malformations, and orofacial clefting in many populations. To test whether TP63 is the disease-causative gene for these phenotypes in Chinese, we recruited two Chinese Ectrodactyly-Ectodermal-dysplasia-Cleft lip/palate syndrome (EEC) cases and a Limb-Mammary-Syndrome (LMS) patient to carry out TP63 gene sequencing. Three missense mutation, c.812G>C (Ser271Thr), c.611G>A (Arg204Gln), and c.680G>A (Arg227Gln), which lead to the substitution of highly conserved amino acids in the DNA-binding domain of TP63, were identified. These mutations were predicted to disrupt DNA-binding specificity and affinity. To our knowledge, this is the first report of EEC and LMS syndromes in individuals of Chinese descent. Analysis of our data demonstrated that TP63 is critical for the development of ectoderm in humans.

p63 in epithelial survival, germ cell surveillance, and neoplasia

The p53homolog p63has emerged as a gene with an enormously complex function that is distinct from that of p53. It encodes two distinct transcript isoforms that have a dramatic impact on replenishment of cutaneous epithelial stem cells and on ovarian germ cell survival. However, although these two fundamental roles of p63 attest to its powerful place in development, its other functions-specifically the apparent capacity of p63, when induced, to supervise the emergence of new cell populations in the breast, prostate, cervix, and upper reproductive tract-are shared by embryo and adult. These observed functions may only scratch the surface of a repertoire that has been postulated to encompass a range of cellular activities, as evidenced by the fact that p63 proteins have been shown to potentially bind to over 5800 target sites. Whether tumorigenic pathways are also involved, and to what extent, is a subject of both promise and controversy that remains to be resolved.

Spectrum of p63 mutations in a selected patient cohort affected with ankyloblepharon-ectodermal defects-cleft lip/palate syndrome (AEC)

Heterozygous mutations in the p63 gene underlie a group of at least seven allelic syndromes, including ankyloblepharon-ectodermal defects-cleft lip/palate syndrome (AEC) and Rapp Hodgkin syndrome (RHS), which involves varying degrees of ectodermal dysplasia, orofacial clefting and limb malformations. Mutations in the AEC and Rapp Hodgkin syndromes cluster in the 3' end of the p63 gene. Previously reported mutations are mainly missense and frameshift mutations in exons 13 and 14, affecting the p63alpha-specific SAM (sterile alpha motif) and TI (transactivation inhibitory) domains. A patient cohort affected by AEC syndrome was evaluated during International Research Symposium supported by the National Foundation for Ectodermal Dysplasias. Nineteen patients underwent full clinical evaluations and 18 had findings consistent with a diagnosis of AEC syndrome. These 19 patients, along with 5 additional relatives had genomic DNA analysis. Twenty-one of the 24 participants from 12 families were found to have mutations in the p63 gene. Eleven different mutations were identified; 10 were novel mutations. Eight were missense mutations within the coding region of the SAM domain. Three other mutations were located in exon 14 sequences, which encode the TI domain. The effects of the mutations in the SAM and TI domains are poorly understood and functional studies are required to understand the pathological mechanisms. However, AEC and RHS mutations in the 5' and 3' ends of the p63 gene point towards a critical role of the DeltaNp63alpha isoform for the AEC/RHS phenotype.

Craniofacial and anthropometric phenotype in ankyloblepharon-ectodermal defects-cleft lip/palate syndrome (Hay-Wells syndrome) in a cohort of 17 patients

Ankyloblepharon-ectodermal dysplasia-cleft lip/palate (AEC) syndrome and Rapp-Hodgkin syndrome are well-characterized clinical entities caused by mutations in the TP63 gene. While AEC and Rapp-Hodgkin had been thought to be clinically distinct entities, the elucidation of their molecular etiology confirmed that they are a clinical continuum as opposed to distinct disorders. We have evaluated 17 patients with AEC syndrome using a systematic clinical approach. In our study, we have identified new features and others that were thought to occur only rarely. These include short stature and poor weight gain with preservation of head circumference in nearly all subjects, trismus in 35% and hypospadias in 78% of males. In addition, we describe the frequency of phenotypic features and demonstrate the extreme clinical variability in the largest cohort of AEC individuals reported in the literature thus far.

DeltaNp63 knockdown mice: A mouse model for AEC syndrome

Dominant mutations in TP63 cause ankyloblepharon ectodermal dysplasia and clefting (AEC), an ectodermal dysplasia characterized by skin fragility. Since DeltaNp63alpha is the predominantly expressed TP63 isoform in postnatal skin, we hypothesized that mutant DeltaNp63alpha proteins are primarily responsible for skin fragility in AEC patients. We found that mutant DeltaNp63alpha proteins expressed in AEC patients function as dominant-negative molecules, suggesting that the human AEC skin phenotype could be mimicked in mouse skin by downregulating DeltaNp63alpha. Indeed, downregulating DeltaNp63 expression in mouse epidermis caused severe skin erosions, which resembled lesions that develop in AEC patients. In both cases, lesions were characterized by suprabasal epidermal proliferation, delayed terminal differentiation, and basement membrane abnormalities. By failing to provide structural stability to the epidermis, these defects likely contribute to the observed skin fragility. The development of a mouse model for AEC will allow us to further unravel the genetic pathways that are normally regulated by DeltaNp63 and that may be perturbed in AEC patients. Ultimately, these studies will not only contribute to our understanding of the molecular mechanisms that cause skin fragility in AEC patients, but may also result in the identification of targets for novel therapeutic approaches aimed at treating skin erosions. (c) 2009 Wiley-Liss, Inc.

Differential PERP regulation by TP63 mutants provides insight into AEC pathogenesis

Ankyloblepharon Ectodermal Dysplasia and Cleft Lip/Palate (AEC) or Hay-Wells Syndrome is an autosomal dominant disorder characterized by a variety of phenotypes in ectodermal derivatives, including severe skin erosions, ankyloblepharon, coarse and wiry hair, scalp dermatitis, and dystrophic nails. AEC is caused by mutations in the gene encoding the TP63 transcription factor, specifically in the Sterile Alpha Motif (SAM) domain. The exact mechanism, however, by which these specific TP63 mutations lead to the observed spectrum of phenotypes is unclear. Analysis of individual TP63 target genes provides a means to understand specific aspects of the phenotypes associated with AEC. PERP is a TP63 target critical for cell-cell adhesion due to its participation in desmosomal adhesion complexes. As PERP null mice display symptoms characteristic of ectodermal dysplasia syndromes, we hypothesized that PERP dysfunction might contribute to AEC. Using luciferase reporter assays, we demonstrate here that PERP induction is in fact compromised with some, but not all, AEC-patient derived TP63 mutants. Through analysis of skin biopsies from AEC patients, we show further that a subset of these display aberrant PERP expression, suggesting the possibility that PERP dysregulation is involved in the pathogenesis of this disease. These findings demonstrate that distinct AEC TP63 mutants can differentially compromise expression of downstream targets, providing a rationale for the variable spectra of symptoms seen in AEC patients. Elucidating how specific TP63 target genes contribute to the pathogenesis of AEC will ultimately help design novel approaches to diagnose and treat AEC.

AEC syndrome caused by a novel p63 mutation and demonstrating erythroderma followed by extensive depigmentation

We present an infant with AEC syndrome due to a novel TP63 mutation (F552S), who demonstrated neonatal erythroderma followed by extensive depigmentation. We are unaware of previous reports highlighting the extensive depigmentation present in our patient.

Rapp-Hodgkin ectodermal dysplasia syndrome: the clinical and molecular overlap with Hay-Wells syndrome

We report on the clinical and molecular abnormalities in a 7-month-old girl and her mother with an ectodermal dysplasia disorder that most closely resembles Rapp-Hodgkin syndrome (RHS). At birth, the child had bilateral cleft palate, a narrow pinched nose, small chin, and hypoplastic nipples, and suffered from respiratory distress, feeding difficulties, and poor weight gain, although developmental progress was normal. Her mother had a cleft palate, sparse hair, high forehead, dental anomalies, a narrow nose, dysplastic nails, and reduced sweating. Sequencing of the p63 gene in genomic DNA from both individuals revealed a heterozygous frameshift mutation, 1721delC, in exon 14. This mutation has not been described previously and is the seventh report of a pathogenic p63 gene mutation in RHS. The frameshift results in changes to the tail of p63 with the addition of 90 missense amino acids downstream and a delayed termination codon that extends the protein by 21 amino acids. This mutation is predicted to disrupt the normal repressive function of the transactivation inhibitory domain leading to gain-of-function for at least two isoforms of the p63 transcription factor. The expanding p63 mutation database demonstrates that there is considerable overlap between the molecular pathology of RHS and Hay-Wells syndrome, with identical mutations in some cases, and that these two disorders may in fact be synonymous.

A rare association of B cell lymphoma and ectodermal dysplasia presenting with protein-losing enteropathy

This patient, known to have ectodermal dysplasia, was referred to the hospital to investigate the cause for his significant pedal oedema and hypoproteinaemia. Investigations ruled out protein loss from the kidney and there was no evidence of chronic liver disease. Protein-losing enteropathy became a diagnosis of exclusion. To investigate it further, he underwent an oral gastroduodenoscopy and a computed tomography scan of the abdomen, which showed an abnormal duodenal mucosa and extensive retroperitoneal lymphadenopathy. Biopsies confirmed this to be grade II follicular non-Hodgkin lymphoma. The lymphadenopathy was causing obstructive hydronephrosis, which required a nephrostomy. He received a course of steroids and chemotherapy. His condition, however, deteriorated and he died.

SAM domain-based protein oligomerization observed by live-cell fluorescence fluctuation spectroscopy

Sterile-alpha-motif (SAM) domains are common protein interaction motifs observed in organisms as diverse as yeast and human. They play a role in protein homo- and hetero-interactions in processes ranging from signal transduction to RNA binding. In addition, mutations in SAM domain and SAM-mediated oligomers have been linked to several diseases. To date, the observation of heterogeneous SAM-mediated oligomers in vivo has been elusive, which represents a common challenge in dissecting cellular biochemistry in live-cell systems. In this study, we report the oligomerization and binding stoichiometry of high-order, multi-component complexes of (SAM) domain proteins Ste11 and Ste50 in live yeast cells using fluorescence fluctuation methods. Fluorescence cross-correlation spectroscopy (FCCS) and 1-dimensional photon counting histogram (1dPCH) confirm the SAM-mediated interaction and oligomerization of Ste11 and Ste50. Two-dimensional PCH (2dPCH), with endogenously expressed proteins tagged with GFP or mCherry, uniquely indicates that Ste11 and Ste50 form a heterogeneous complex in the yeast cytosol comprised of a dimer of Ste11 and a monomer of Ste50. In addition, Ste50 also exists as a high order oligomer that does not interact with Ste11, and the size of this oligomer decreases in response to signals that activate the MAP kinase cascade. Surprisingly, a SAM domain mutant of Ste50 disrupted not only the Ste50 oligomers but also Ste11 dimerization. These results establish an in vivo model of Ste50 and Ste11 homo- and hetero-oligomerization and highlight the usefulness of 2dPCH for quantitative dissection of complex molecular interactions in genetic model organisms such as yeast.

A novel translation re-initiation mechanism for the p63 gene revealed by amino-terminal truncating mutations in Rapp-Hodgkin/Hay-Wells-like syndromes

Missense mutations in the 3' end of the p63 gene are associated with either RHS (Rapp-Hodgkin syndrome) or AEC (Ankyloblepharon Ectodermal defects Cleft lip/palate) syndrome. These mutations give rise to mutant p63alpha protein isoforms with dominant effects towards their wild-type counterparts. Here we report four RHS/AEC-like patients with mutations (p.Gln9fsX23, p.Gln11X, p.Gln16X), that introduce premature termination codons in the N-terminal part of the p63 protein. These mutations appear to be incompatible with the current paradigms of dominant-negative/gain-of-function outcomes for other p63 mutations. Moreover it is difficult to envisage how the remaining small N-terminal polypeptide contributes to a dominant disease mechanism. Primary keratinocytes from a patient containing the p.Gln11X mutation revealed a normal and aberrant p63-related protein that was just slightly smaller than the wild-type p63. We show that the smaller p63 protein is produced by translation re-initiation at the next downstream methionine, causing truncation of a non-canonical transactivation domain in the DeltaN-specific isoforms. Interestingly, this new DeltaDeltaNp63 isoform is also present in the wild-type keratinocytes albeit in small amounts compared with the p.Gln11X patient. These data establish that the p.Gln11X-mutation does not represent a null-allele leading to haploinsufficiency, but instead gives rise to a truncated DeltaNp63 protein with dominant effects. Given the nature of other RHS/AEC-like syndrome mutations, we conclude that these mutations affect only the DeltaNp63alpha isoform and that this disruption is fundamental to explaining the clinical characteristics of these particular ectodermal dysplasia syndromes.

Human genetic factors in nonsyndromic cleft lip and palate: an update

Nonsyndromic cleft lip and/or palate (or orofacial cleft, OFC) is a malformation characterized by an incomplete separation between nasal and oral cavities without any associated anomalies. The last point defines the distinction between syndromic and nonsyndromic OFC. Nonsyndromic OFC is one of the most common malformations among live births and is composed of two separate entities: cleft lip with or without cleft palate (CL+/-P) and cleft palate isolated (CPI). Because of the complex etiology of nonsyndromic OFC, which is due to the differences between CL+/-P and CPI, and the heterogeneity of each group, caused by the number of genes involved, the type of inheritance, and the interaction with environmental factors, we reviewed those genes and available loci in the literature whose involvement in the onset of nonsyndromic OFC has more sound scientific evidence. Genetic studies on human populations have demonstrated that CL+/-P and CPI have distinct genetic backgrounds and, therefore, environmental factors probably disclose only these malformations. In CL+/-P several loci, OFC from 1 to 10 have been identified. The first locus, OFC1, has been mapped to chromosome 6p24. Other CL+/-P loci have been mapped to 2p13 (OFC2), 19q13.2 (OFC3) and 4q (OFC4). OFC5-8 are identified by mutations in the MSX1, IRF6, PVRL1, and TP73L gene, respectively. OFC9 maps to 13q33.1-q34, whereas OFC10 is associated with haploinsufficiency of the SUMO1 gene. In addition, MTHFR, TGF-beta3, and RARalpha play a role in cleft onset. In CPI one gene has been identified (TBX22) at present, but others are probably involved. Greater efforts are necessary in order to have a complete picture of the main factors involved in lip and palate formation. These elements will permit us to better understand and better treat patients affected by OFC.

Cleft lip and palate repair in Hay-Wells/ankyloblepharon-ectodermal dysplasia-clefting syndrome

Hay-Wells/ankyloblepharon-ectodermal dysplasia-clefting syndrome is a rare autosomal dominant disorder characterized by ankyloblepharon, ectodermal dysplasia, and cleft lip and/or cleft palate. Mutations in the p63 gene recently have been shown to be etiologic in the majority of cases of ankyloblepharon-ectodermal dysplasia-clefting syndrome. To date, there have been no reports to document wound healing after cleft lip and/or palate repair in ankyloblepharon-ectodermal dysplasia-clefting patients. We describe two patients with ankyloblepharon-ectodermal dysplasia-clefting syndrome and provide a review of the literature. There have been no reported instances of wound healing complications in affected patients. Seventeen percent (3/18) of reported patients required revisions or repair of oronasal fistulae. Cleft lip and palate repair can be performed safely in patients with Hay-Wells syndrome.

Pattern of p63 mutations and their phenotypes--update

Heterozygous mutations in the transcription factor gene p63 cause at least six different syndromes with various combinations of ectodermal dysplasia, orofacial clefting and limb malformations. Here we will present an update of mutations in the p63 gene together with a comprehensive overview of the associated clinical features in 227 patients. These data confirm the previously recognized genotype-phenotype associations. Moreover, we report that there is a large degree of clinical variability in each of the p63-associated disorders. This is illustrated by the different phenotypes that are seen for the five-hotspot mutations that explain almost 90% of all EEC syndrome patients.

De novo missense mutation, S541Y, in the p63 gene underlying Rapp-Hodgkin ectodermal dysplasia syndrome

Rapp-Hodgkin syndrome (RHS) is an autosomal dominant disorder characterized by ectodermal dysplasia and cleft lip/cleft palate. Very recently, mutations in p63 have been identified as a cause of RHS; to date five such mutations have been identified. We describe a Thai girl with RHS. She had short stature, ectodermal dysplasia, epiphora, cleft lip, cleft palate, and normal development. Mutation analysis for the entire coding region of p63 identified a novel and de novo mutation, 1622C--> A (S541Y), in the SAM domain, predicting an abnormal alpha tail of the p63alpha protein isotypes. This observation supports that majority of patients with RHS are caused by mutations affecting the tail of p63alpha, a region that also contains most of the pathogenic mutations in ankyloblepharon-ectodermal dysplasia-clefting (AEC) syndrome.

Rapp-Hodgkin syndrome and the tail of p63

We report the clinical and molecular abnormalities in a 19-year-old woman with Rapp-Hodgkin ectodermal dysplasia syndrome. The physical features include mid-facial hypoplasia, uncombable hair, cleft palate and bifid uvula, lacrimal duct obstruction and dry skin. Sequencing of the p63 gene reveals a new heterozygous frameshift mutation, 1787delG, in exon 14. The frameshift results in changes to the tail of p63 with the addition of 68 missense amino acids downstream and a delayed termination codon that extends the protein length by 21 amino acids. These changes are predicted to disrupt the normal repressive function of the transactivation inhibitory domain leading to gain-of-function for at least two isoforms of the p63 transcription factor. The expanding p63 mutation database demonstrates that there is overlap between Rapp-Hodgkin syndrome and several other ectodermal dysplasia syndromes, notably Hay-Wells syndrome, and that characterization of the functional consequences of these p63 gene mutations at a molecular and cellular level is likely to provide further insight into the clinical spectrum of these developmental malformation syndromes.

Isolated ectrodactyly caused by a heterozygous missense mutation in the transactivation domain of TP63

We report a Mexican boy with isolated ectrodactyly (split hand malformation) in whom a new mutation was identified in exon 3 of the TP63 gene. In contrast to previously reported patients with isolated split hand/foot anomaly and mutations in the DNA binding domain of Tp63, the mutation described herein induce an amino acid substitution (R97C) in the canonical transactivation (TA) domain. To our knowledge, this is the first naturally occurring mutation described so far in this part of the protein. Based on the genotype-phenotype correlation observed in our patient, we hypothesize that integrity of the TA domain of Tp63 is critical for normal limb development.

Genodermatoses 2003-2004

PURPOSE OF REVIEW

Many genodermatoses have been linked in recent years to their respective genes. The underlying biology and integrative nature of these genes with other genes and organ systems is beginning to be understood. This paper reviews recent advances in neurocutaneous disorders, ectodermal dysplasias, and the phenomenon of revertant gene mosaicism.

RECENT FINDINGS

In neurofibromatosis type 1, molecular assays are being developed to distinguish malignant from benign and premalignant lesions. Clinical mutation analysis for the NF1 gene has been problematic; a sensitive new assay using automated comparative sequence analysis may be helpful. Revision of clinical care guidelines is ongoing. New data for the prospective management of optic pathway gliomas is reviewed. The two genes that underlie tuberous sclerosis complex, tuberin and hamartin, lie at the center of an important signal transduction pathway with significant implications for pharmacologic treatment. Issues in genetic counseling for this highly variable disease are updated. Extensive progress has been made in understanding the basis of several forms of ectodermal dysplasia. Disorders caused by mutations in p63 and the connexin and NF-kappaB gene families will be reviewed. Finally, phenotypic in vivo amelioration of genodermatoses via revertant gene mosaicism will be discussed as a possible mechanism to be exploited in directed therapeutic approaches.

SUMMARY

This paper reviews recent developments in the molecular and biologic bases of neurofibromatosis type 1, tuberous sclerosis, and ectodermal disorders related to p63 and the connexin and NF-kappaB gene families. The concept of revertant gene mosaicism is also discussed as a potential model for gene therapy.