Survival is not enough: reflections of a long-term renal patient

A kidney patient recalls his experience of almost 45 years of renal replacement therapy covering nearly 25 years of dialysis and 20 years with a transplant. At the beginning, patient or graft survival was a major goal and symbol of successful treatment. But for the patient, what really matters is the quality of his life, assuming he can survive.

Plectin defects in epidermolysis bullosa simplex with muscular dystrophy

Epidermolysis bullosa simplex with muscular dystrophy (EBS-MD, MIM 226670) is caused by plectin defects. We performed mutational analysis and immunohistochemistry using EBS-MD (n = 3 cases) and control skeletal muscle to determine pathogenesis. Mutational analysis revealed a novel homozygous plectin-exon32 rod domain mutation (R2465X). All plectin/HD1-121 antibodies stained the control skeletal muscle membrane. However, plectin antibodies stained the cytoplasm of type II control muscle fibers (as confirmed by ATPase staining), whereas HD1-121 stained the cytoplasm of type I fibers. EBS-MD samples lacked membrane (n = 3) but retained cytoplasmic HD1-121 (n = 1) and plectin staining in type II fibers (n = 3). Ultrastructurally, EBS-MD demonstrated widening and vacuolization adjacent to the membrane and disorganization of Z-lines (n = 2 of 3) compared to controls (n = 5). Control muscle immunogold labeling colocalized plectin and desmin to filamentous bridges between Z-lines and the membrane that were disrupted in EBS-MD muscle. We conclude that fiber-specific plectin expression is associated with the desmin-cytoskeleton, Z-lines, and crucially myocyte membrane linkage, analogous to hemidesmosomes in skin.

Retrospective diagnosis of Kindler syndrome in a 37-year-old man

Kindler syndrome is a rare autosomal recessive disorder characterized by acral blisters in infancy and early childhood, followed by photosensitivity, progressive poikiloderma and cutaneous atrophy. Other features include webbing of the toes and fingers, palmoplantar hyperkeratosis, gingival fragility, poor dentition, and mucosal involvement in the form of urethral, anal and oesophageal stenosis. The recent finding of KIND1 mutations in Kindler syndrome facilitates early diagnosis, prophylactic measures and more precise definition of the phenotype. In the family described here, molecular diagnosis of Kindler syndrome in an infant with acral blisters led to the belated diagnosis in a severely affected relative whose condition had remained unidentified for 37 years.

A germline mutation in BLOC1S3/reduced pigmentation causes a novel variant of Hermansky-Pudlak syndrome (HPS8)

Hermansky-Pudlak syndrome (HPS) is genetically heterogeneous, and mutations in seven genes have been reported to cause HPS. Autozygosity mapping studies were undertaken in a large consanguineous family with HPS. Affected individuals displayed features of incomplete oculocutaneous albinism and platelet dysfunction. Skin biopsy demonstrated abnormal aggregates of melanosomes within basal epidermal keratinocytes. A homozygous germline frameshift mutation in BLOC1S3 (p.Gln150ArgfsX75) was identified in all affected individuals. BLOC1S3 mutations have not been previously described in patients with HPS, but BLOC1S3 encodes a subunit of the biogenesis of lysosome-related organelles complex 1 (BLOC-1). Mutations in other BLOC-1 subunits have been associated with an HPS phenotype in humans and/or mouse, and a nonsense mutation in the murine orthologue of BLOC1S3 causes the reduced pigmentation (rp) model of HPS. Interestingly, eye pigment formation is reported to be normal in rp, but we found visual defects (nystagmus, iris transilluminancy, foveal hypoplasia, reduced visual acuity, and evidence of optic pathway misrouting) in affected individuals. These findings define a novel form of human HPS (HPS8) and extend genotype-phenotype correlations in HPS.

Prenatal diagnosis for severe inherited skin disorders: 25 years' experience

BACKGROUND

Over the last 25 years there have been major advances in methods for prenatal testing of inherited skin disorders. Since 1979, our group at the St John's Institute of Dermatology has performed 269 prenatal diagnoses, using a variety of approaches, including fetal skin biopsy (FSB), chorionic villus sampling (CVS) and preimplantation genetic diagnosis (PGD).

OBJECTIVES

This study was designed to review the clinical indications, testing procedures and laboratory analyses for all prenatal tests conducted at St John's over this period.

METHODS

FSBs were examined for morphological and, when relevant or feasible, immunohistochemical abnormalities. The DNA-based tests involved screening by nucleotide sequencing, restriction enzyme digests or, in a few cases, by linkage analysis. Results Of the 269 tests, 191 were FSB, 76 were CVS and two were PGD. The major indications for FSB were epidermolysis bullosa (EB) (138 cases, including 88 junctional and 48 dystrophic), ichthyoses (37 cases, including 22 tests for harlequin ichthyosis) and oculocutaneous albinism (12 cases). Of the CVS procedures, 75 were for EB (40 junctional, 35 dystrophic) and one was for the EEC (ectrodactyly, ectodermal dysplasia, clefting) syndrome. Both of the PGD procedures were for the skin fragility-ectodermal dysplasia syndrome. All tests provided accurate diagnoses and the fetal loss rate was approximately 1% for both FSB and CVS.

CONCLUSIONS

The development of prenatal testing has proved to be of great benefit for individuals or couples at risk of having children with severe inherited skin disorders and, in the absence of a cure, prenatal testing along with appropriate counselling has become an important translational benefit of basic research and an integral part of clinical management.

Mutations in ABCA12 underlie the severe congenital skin disease harlequin ichthyosis

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

Increased risk of squamous cell carcinoma in junctional epidermolysis bullosa

Non-Herlitz junctional epidermolysis bullosa (JEB) is an autosomal recessive genodermatosis characterized by skin fragility and blistering. It is usually caused by mutations in the genes encoding the basement membrane proteins laminin 5 or type XVII collagen. Clinically, impaired wound healing and chronic erosions cause major morbidity in affected patients. Previously it was thought that these individuals, unlike patients with dystrophic EB, did not have an increased risk of developing skin cancer. However, we describe three patients with non-Herlitz JEB (aged 42, 56 and 75 years) who developed cutaneous squamous cell carcinomas (SCCs). The tumours were well-differentiated in two cases, but one patient had multiple primary SCCs that were either well- or moderately differentiated. Most cases of SCC in non-Herlitz JEB described have occurred in those with laminin 5 defects and on the lower limbs. These clinicopathological observations have important implications for the management of patients with this mechanobullous disorder as well as providing further insight into the biology of skin cancer associated with chronic inflammation and scarring.

Striate palmoplantar keratoderma arising from desmoplakin and desmoglein 1 mutations is associated with contrasting perturbations of desmosomes and the keratin filament network

BACKGROUND

Several hereditary human diseases are now known to be caused by distinct mutations in genes encoding various desmosome components. Although the effects of some of these mutant genes have been analysed by targeted disruption experiments in mouse models, little is known about the cell and tissue changes in affected human patients.

OBJECTIVES

To investigate the effects of heterozygous nonsense mutations in desmoplakin (Dp) and desmoglein (Dsg) 1 which cause the autosomal dominant disorder striate palmoplantar keratoderma (SPPK), focusing on changes in desmosome structure and composition and the associated keratin intermediate filament (KIF) network in palm skin, and in cultured keratinocytes generated from the same site.

METHODS

We analysed palm and nonpalm skin sections from four SPPK patients with Dp mutations and one patient with a Dsg1 mutation with respect to tissue and subcellular morphologies, and correlated the in vivo and in vitro findings.

RESULTS

Using electron microscopy, we found abnormalities of desmosomes and cell-cell adhesion in the suprabasal layers in the epidermis from patients with both Dsg1- and Dp-associated SPPK. These changes were more advanced in skin from patients with Dp mutations. Both Dp and Dsg1 mutations were accompanied by significantly reduced numbers of desmosomes in the suprabasal layers, while decreased desmosome size was evident only in Dsg1-associated SPPK. Confocal microscopy analysis showed marked differences in the expression of keratins and of desmosome components, both between the two types of SPPK, and between SPPK and normal skin. The expression of keratins K5, K14 and K10 was reduced in Dsg1-associated SPPK skin, whereas perinuclear aggregation of keratin filaments was more evident in Dp-associated SPPK. In both types of SPPK upregulation of K16 was pronounced and involucrin labelling was abnormal.

CONCLUSIONS

Mutations in Dp and Dsg1 genes causing SPPK may be associated with perturbations in epidermal differentiation accompanied by a marked disruption of several components of the epidermal scaffold including desmosomes and the KIF network.

Reduced Expression of Insulin-Like Growth Factor-Binding Protein-3 (IGFBP-3) in Squamous Cell Carcinoma Complicating Recessive Dystrophic Epidermolysis Bullosa

Squamous cell carcinoma (SCC) is a common complication in individuals with recessive dystrophic epidermolysis bullosa (RDEB). For the severe Hallopeau-Siemens subtype, the mortality rate from SCC is over 55% by the age of 40 y. Currently, little is known about the molecular pathology or cell biology of SCC in RDEB. In this study, we compared gene expression in RDEB SCC (n=3) and non-EB SCC (n=3) with corresponding RDEB and non-EB peri-tumoral skin, with microarray analysis using DermArray membranes as well as semi-quantitative and real-time RT-PCR. Both tumor sets showed downregulation of epidermal differentiation markers (e.g., profilaggrin, keratins 1 and 10) as well as certain pro-apoptotic genes (e.g., death-associated kinase-3 or ZIP kinase). Likewise, in both groups there was upregulation of matrix metalloproteinase 1 and laminin 5 in the tumors. But we found that the expression of insulin-like growth factor-binding protein-3 (IGFBP-3) was lower (mean of 5.8-fold) in RDEB SCC compared with non-EB SCC. These data were verified by immunohistochemistry. IGFBP-3 has an important role in cancer cell apoptosis mediated via the nuclear retinoid X receptor alpha (RXRalpha). Reduced expression of IGFBP-3 in RDEB SCC may provide a partial explanation for the aggressive behavior and poor prognosis of these tumors in this genodermatosis.

Recurrent mutations in kindlin-1, a novel keratinocyte focal contact protein, in the autosomal recessive skin fragility and photosensitivity disorder, Kindler syndrome

Kindler syndrome (OMIM 173650) is a rare autosomal recessive disorder characterized by trauma-induced blister formation (especially in childhood) and photosensitivity. Other features include mucocutaneous scarring and progressive poikiloderma. There is also an increased risk of skin and mucous membrane malignancy. The disorder was recently mapped to 20p12.3 and pathogenic mutations were identified in a new gene, KIND1. This gene encodes a 677 amino acid protein, kindlin-1, a component of focal contacts in keratinocytes. In this study, we identified four new recurrent mutations in KIND1 in 16 individuals with Kindler syndrome from 13 families of Pakistani (676insC), UK Caucasian (E304X), Omani (W616X), or Italian (958-1G > A) origins. Haplotype analysis demonstrated common ancestral mutant alleles for each mutation, apart from one of the six Pakistani families in which the mutation 676insC (which occurs in a repeat of seven cytosines) was present on a different genetic background. All mutations were homozygous, apart from the three UK Caucasian cases that were all compound heterozygotes (second allele mutations: L302X, 1161delA, 1909delA). All mutations were associated with markedly reduced or absent skin immunostaining with an antikindlin-1 antibody. These loss-of-function KIND1 mutations demonstrate the importance of kindlin-1 in maintaining epithelial integrity, although the mechanism linking this mutant protein to photosensitivity and poikiloderma remains to be determined. Delineation of these recurrent mutations is also relevant to optimizing mutation detection strategies in Kindler syndrome patients from particular ethnic backgrounds.

Gap junction development in the human fetal hair follicle and bulge region

BACKGROUND

Gap junctions, composed of connexin (Cx) subunits, are channels that allow intercellular communication between adjacent cells and are thought to play a key role in the regulation of cell proliferation and differentiation. The Cx expression pattern and formation of gap junctions in human fetal hair follicles has yet to be clarified, including the prominent follicular bulge region that is believed to be a site rich in stem cells.

OBJECTIVES

To study the expression of two major Cxs, Cx26 and Cx43, in developing hair follicles in skin samples from a series of human fetuses of estimated gestational age (EGA) 88-163 days, and to determine quantitatively the presence of gap junctions.

METHODS

We used immunofluorescence labelling to investigate the sequential expression pattern of Cx26 and Cx43 in developing human hair follicles. Gap junction formation was observed by electron microscopy and the numbers of gap junctions were analysed quantitatively. Results Both Cx26 and Cx43 expression were observed at 88 days' EGA in the inner part of the hair peg. At 135 days' EGA, Cx26 was expressed in the outer root sheath (ORS) and the inner root sheath (IRS), while Cx43 was expressed chiefly in the IRS, hair matrix and sebaceous glands. At 163 days' EGA, Cx26 expression was most intense in the outermost layer of the ORS, in contrast to Cx43 expression which was in the inner part of the ORS. In the bulge region, only Cx43 was expressed in a subset of cells in the bulge. Ultrastructurally, gap junctions were observed at 102 days' EGA in the hair peg, and the number of gap junctions increased as the hair follicle matured. Gap junctions were also observed between the bulge cells in considerable numbers.

CONCLUSIONS

The changing expression patterns of Cx26 and Cx43 and the increasing gap junction numbers suggest a close association of Cx expression and gap junction formation with hair follicle morphogenesis. In addition, the present ultrastructural observations demonstrate that considerable numbers of the bulge cells, a putative site rich in hair follicle stem cells, form gap junctions during human hair follicle development.

Efficacy and safety of endoscopic dilation of esophageal strictures in epidermolysis bullosa

BACKGROUND

Epidermolysis bullosa is a rare genetically determined disorder of the stratified squamous epithelium. Patients with the most severe forms develop scarring of the esophagus after ingestion of food. This results in dysphagia, which severely compromises the ability to eat. Maintenance of adequate nutritional intake is a central aim, but the most appropriate method is unknown.

METHODS

The results of endoscopic through-the-scope balloon dilation under propofol anesthesia in 53 patients with epidermolysis bullosa and esophageal strictures are reported.

RESULTS

Seventy-five percent of patients had a single stricture (range 1 to 6 strictures), most often in the proximal esophagus (median 20 cm from incisors). A total of 182 dilations were performed (median two per patient) over a median follow-up period of 3.5 years. For all but 3 patients, there was an improvement in the dysphagia score. There was a mean increase in weight after the procedure of 2.9 kg: 95% CI[2.0, 3.8]; p<0.001, over a median 29 days. There was no significant post-procedure morbidity.

CONCLUSIONS

Endoscopic balloon dilation is a safe and effective treatment for the esophageal strictures of epidermolysis bullosa. In the majority of patients, dilation relieves dysphagia and improves nutritional status.

Desmosomal proteins, including desmoglein 3, serve as novel negative markers for epidermal stem cell-containing population of keratinocytes

No single method has been universally adopted for identifying and isolating epidermal stem/progenitor cells, and the emergence of new markers of stem cell populations is worth exploring. Here we report, for the first time, that clusters of basal keratinocytes at the tips of the rete ridges in human palm, previously recognised as a major repository of stem cells, had very low levels of desmoplakin protein and mRNA expression, compared with cells at the sides of the ridges or above the dermal papillae. We found that in populations of palm keratinocytes, selected by their ability to adhere rapidly to type IV collagen, there were significantly reduced levels of desmoplakin and other major desmosome proteins. We then showed that a low desmoglein 3 (Dsg3) expression on the cell surface could be used to enrich for a cell population with high clonogenecity, colony forming efficiency and enhanced proliferative potential, but with a low ability to form the abortive clones, compared with populations with a higher Dsg3 expression. Moreover, stringent sorting of populations showing both beta1 integrin-bright and Dsg3-dull expression enabled even further enrichment of a population containing the putative epidermal stem cells. These findings provide the basis for a new strategy for epidermal stem/progenitor cell enrichment, and encourage further study of the role of desmosomes in stem cell biology.

Dilemmas in distinguishing between dominant and recessive forms of dystrophic epidermolysis bullosa

BACKGROUND

Dystrophic epidermolysis bullosa (DEB) is a heterogeneous inherited blistering skin disorder. The mode of inheritance may be autosomal dominant or recessive but all forms of DEB result from mutations in the gene encoding the anchoring fibril protein, type VII collagen, COL7A1. Consequently, in spite of careful clinical and skin biopsy examination, it may be difficult to distinguish mild recessive cases from de novo dominant disease in families with clinically normal parents and no other affected siblings; this distinction has significant implications for the accuracy of genetic counselling.

OBJECTIVES

To assess whether COL7A1 mutation analysis might help determine mode of inheritance in mild to moderate DEB.

METHODS

We performed COL7A1 screening using heteroduplex analysis and direct nucleotide sequencing in four individuals with mild to moderate "sporadic" DEB and clinically unaffected parents.

RESULTS

In each patient, we identified a heterozygous glycine substitution within the type VII collagen triple helix. However, in two cases these mutations had been inherited in trans with a non-sense mutation on the other allele (i.e. autosomal recessive DEB). In the other two cases, no additional mutation was identified and neither mutation was present in parental DNA (i.e. de novo dominant disease).

CONCLUSIONS

This study highlights the usefulness of DNA sequencing in determining the inherited basis of some sporadic cases of DEB. However, delineation of glycine substitutions should prompt comprehensive COL7A1 gene sequencing in the affected individual, as well as clinical assessment of parents and mutation screening in parental DNA, if the true mode of inheritance is to be established correctly.

An unusual N-terminal deletion of the laminin alpha3a isoform leads to the chronic granulation tissue disorder laryngo-onycho-cutaneous syndrome

Laryngo-onycho-cutaneous (LOC or Shabbir) syndrome (OMIM 245660) is an autosomal recessive epithelial disorder confined to the Punjabi Muslim population. The condition is characterized by cutaneous erosions, nail dystrophy and exuberant vascular granulation tissue in certain epithelia, especially conjunctiva and larynx. Genome-wide homozygosity mapping localized the gene to a 2 Mb region on chromosome 18q11.2 with an LOD score of 19.8 at theta=0. This region includes the laminin alpha3 gene (LAMA3), in which loss-of-expression mutations cause the lethal skin blistering disorder Herlitz junctional epidermolysis bullosa. Detailed investigation showed that this gene possesses a further 38 exons (76 exons in total) spanning 318 kb of genomic DNA, and encodes three distinct proteins, designated laminin alpha3a, alpha3b1 and alpha3b2. The causative mutation in 15 families was a frameshift mutation 151insG predicting a stop codon 7 bp downstream in an exon that is specific to laminin alpha3a. This protein is secreted only by the basal keratinocytes of stratified epithelia, implying that LOC is caused by dysfunction of keratinocyte-mesenchymal communication. Surprisingly, the 151insG mutation does not result in nonsense-mediated mRNA decay due to rescue of the transcript by an alternative translation start site 6 exons downstream. The resultant N-terminal deletion of laminin alpha3a was confirmed by immunoprecipitation of secreted proteins from LOC keratinocytes. These studies show that the laminin alpha3a N-terminal domain is a key regulator of the granulation tissue response, with important implications not only in LOC but in a range of other clinical conditions associated with abnormal wound healing.

Lack of plakophilin 1 increases keratinocyte migration and reduces desmosome stability

Ablation of the desmosomal plaque component plakophilin 1 underlies the autosomal recessive genodermatosis, skin fragility-ectodermal dysplasia syndrome (OMIM 604536). Skin from affected patients is thickened with increased scale, and there is loss of adhesion between adjacent keratinocytes, which exhibit few small, poorly formed desmosomes. To investigate further the influence of plakophilin 1 on keratinocyte adhesion and desmosome morphology, we compared plakophilin 1-deficient keratinocytes (vector controls) with those expressing recombinant plakophilin 1 introduced by retroviral transduction. We found that plakophilin 1 increases desmosomal protein content within the cell rather than enhancing transcriptional levels of desmosomal genes. Re-expression of plakophilin 1 in null cells retards cell migration but does not alter keratinocyte cell growth. Confluent sheets of plakophilin 1-deficient keratinocytes display fewer calcium-independent desmosomes than do plakophilin 1-deficient keratinocytes expressing recombinant plakophilin 1 or keratinocytes expressing endogenous plakophilin 1. In addition electron microscopy studies show that re-expression of plakophilin 1 affects desmosome size and number. Collectively, these results demonstrate that restoration of plakophilin 1 function in our culture system influences the transition of desmosomes from a calcium-dependent to a calcium-independent state and this correlates with altered keratinocyte migration in response to wounding. Thus, plakophilin 1 has a key role in increasing desmosomal protein content, in desmosome assembly, and in regulating cell migration.

Desmosomes exhibit site-specific features in human palm skin

Hereditary skin disorders resulting from desmosome gene pathology may preferentially involve the palms and soles. Why this is so is not clear. Moreover, even in normal control skin it is unknown whether there are differences in desmosome number, size or structural organization in palmoplantar sites compared with skin from other body regions. Therefore, we sought evidence for such differences by examining desmosome expression in relation to epidermal differentiation in both epidermis and cultured keratinocytes from normal human palm and breast skin samples. Confocal microscopy of skin biopsy material showed relative differences in the expression profiles of several desmosomal proteins (desmogleins, desmocollins, desmoplakin, plakoglobin and plakophilin 1) between the two sites. Western blotting revealed a higher expression level of all five proteins in palm compared with breastcultured keratinocytes. Staining for the differentiation-associated component, involucrin, suggested an earlier onset of synthesis of this protein in palm epidermis, and a suspension-induced differentiation assay showed that involucrin synthesis began earlier in palm keratinocytes than in breast cells. At 4-8 h, the number of involucrin-positive cells in palm keratinocytes was almost twice that in breast. Morphometric analysis showed that, overall, desmosomes were larger but of similar population density in the palm compared with breast skin. These findings demonstrate differences in desmosome structure and protein expression between the two sites, possibly reflecting the needs of palms and soles to withstand constant mechanical stress. They may also help to explain the preferential involvement of this region in certain hereditary disorders (palmoplantar keratodermas), associated with mutations in desmoplakin or desmoglein 1.

Alterations in desmosome size and number coincide with the loss of keratinocyte cohesion in skin with homozygous and heterozygous defects in the desmosomal protein plakophilin 1

Recessive mutations in the desmosomal plaque protein plakophilin 1 (PkP1) underlie ectodermal dysplasia/skin fragility syndrome (MIM 604536). We undertook an immunohistochemical and quantitative electron microscopic examination of suprabasal desmosomes from 4 skin samples from 3 PkP1 deficient patients, an unaffected carrier with a PKP1 heterozygous acceptor splice site mutation and 5 healthy control subjects. Desmosomal plaque size (>50 desmosomes per individual) and frequency (>20 high power fields, HPF) were assessed. Compared with controls, desmosomes were reduced dramatically both in size (49%) and frequency (61%) in the lower suprabasal layers (LSB) in PkP1 null patients (P<0.01). In the LSB compartment of the heterozygous carrier, corresponding reductions were 37% and 20%, respectively (P<0.01). Surprisingly, the PkP1 null patient's upper suprabasal layer, (USB), desmosome size was larger (59%, P<0.01) than the control value, and showed increased desmoglein 1 and PkP2 USB staining. The USB desmosome frequency in PKP1 null patients was similar to the LSB compartment (but reduced by 43% compared to USB controls). The carrier showed no difference in the USB desmosome size and frequency compared with the controls (P>0.05). The PKP1 null patients showed poorly developed inner and outer desmosomal plaques. Thus, both the patients and unaffected carrier showed reductions in the LSB desmosome size and number; despite only PkP1 null patients exhibiting any phenotype. These findings attest to the molecular recruiting and stabilizing roles of PkP1 in desmosome formation, particularly in the LSB compartment.

Loss of kindlin-1, a human homolog of the Caenorhabditis elegans actin-extracellular-matrix linker protein UNC-112, causes Kindler syndrome

Kindler syndrome is an autosomal recessive disorder characterized by neonatal blistering, sun sensitivity, atrophy, abnormal pigmentation, and fragility of the skin. Linkage and homozygosity analysis in an isolated Panamanian cohort and in additional inbred families mapped the gene to 20p12.3. Loss-of-function mutations were identified in the FLJ20116 gene (renamed "KIND1" [encoding kindlin-1]). Kindlin-1 is a human homolog of the Caenorhabditis elegans protein UNC-112, a membrane-associated structural/signaling protein that has been implicated in linking the actin cytoskeleton to the extracellular matrix (ECM). Thus, Kindler syndrome is, to our knowledge, the first skin fragility disorder caused by a defect in actin-ECM linkage, rather than keratin-ECM linkage.

Psoriasis bullosa acquisita

We report a 51-year-old man with a 20-year history of chronic plaque psoriasis who developed an autoimmune subepidermal blistering eruption that had clinical features of bullous pemphigoid, erythema multiforme and epidermolysis bullosa acquisita. Investigations revealed a 1 : 400 titre circulating and in vivo bound IgG autoantibody that mapped to the dermal side of 1 m NaCl-split skin and localized to the lower lamina lucida/upper lamina densa on immunogold electron microscopy. Immunoblotting, using dermal extracts, showed serum binding to antigens of approximately 200- and approximately 260 kDa. Indirect immunofluorescence microscopy, using the patient's serum on archival skin sections taken from selected individuals with different forms of inherited epidermolysis bullosa as substrate, showed normal basement membrane labelling on all samples apart from recessive dystrophic epidermolysis bullosa skin (with inherent mutations in the type VII collagen gene): in these cases there was a complete absence of immunostaining. Clinically, the patient responded rapidly to combination treatment with intravenous immunoglobulin and oral corticosteroids, dapsone and mycophenolate mofetil. Autoimmune subepidermal blistering has been reported in other patients with psoriasis, although no specific target antigen has ever been determined. Our study provides preliminary evidence that, for this patient at least, the autoantibody may be targeted against a skin component closely associated with type VII collagen (the epidermolysis bullosa acquisita antigen). Therefore, we propose the term 'psoriasis bullosa acquisita' for this and possibly other patients with similar skin eruptions.

Changes in gap junction distribution and connexin expression pattern during human fetal skin development

Gap junctions are intercellular channels composed of connexin subunits that mediate cell-cell communication. The functions of gap junctions are believed to be associated with cell proliferation and differentiation and to be important in maintaining tissue homeostasis. We therefore investigated the expression of connexins (Cx)26 and 43, the two major connexins in human epidermis, and examined the formation of gap junctions during human fetal epidermal development. By immunofluorescence, Cx26 expression was observed between 49 and 96 days' estimated gestational age (EGA) but was not present from 108 days' EGA onwards. Conversely, Cx43 expression was observed from 88 days' EGA onwards. Using electron microscopy, the typical structure of gap junctions was observed from 120 days' EGA. The number of gap junctions increased over time and they were more common in the upper layers, within the periderm and intermediate keratinocyte layers rather than the basal layer. Immunoelectron microscopy revealed Cx43 labeling on the gap junction structures after 105 days' EGA. Formation of gap junctions increased as skin developed, suggesting that gap junctions may play an important role in fetal skin development. Furthermore, the changing patterns of connexin expression suggest that Cx26 is important for early fetal epidermal development.

Genotype-phenotype correlation in skin fragility-ectodermal dysplasia syndrome resulting from mutations in plakophilin 1

We report a 42-year-old Japanese man with an unusual autosomal recessive genodermatosis. The clinical features comprised normal skin at birth, loss of scalp hair at 3-months of age after a febrile illness, progressive nail dystrophy during infancy, palmoplantar keratoderma starting around the age of 18 years and trauma-induced skin fragility and blisters noted from the age of 20 years. Skin biopsy of rubbed non-lesional skin revealed widening of spaces between adjacent keratinocytes from the suprabasal layer upwards. Electron microscopy demonstrated a reduced number of hypoplastic desmosomes. Immunohistochemical labeling showed a reduction in intercellular staining for the desmosome component plakophilin 1. Mutation analysis revealed a homozygous intron 11 donor splice site mutation in the plakophilin 1 gene, 2021+1 G>A (GenBank no. Z34974). RT-PCR, using RNA extracted from the skin biopsy, provided evidence for residual low levels of the full-length wild-type transcript (approximately 8%) as well as multiple other near full-length transcripts, one of which was in frame leading to deletion of 17 amino acids from the 9th arm-repeat unit of the plakophilin 1 tail domain. Thus, the molecular findings help explain the clinical features in the patient, who has a similar but milder phenotype to previously reported patients with skin fragility-ectodermal dysplasia syndrome associated with complete ablation of plakophilin 1 (OMIM 604536). This new 'mitis' phenotype provides further clinicopathological evidence for the role of plakophilin 1 in keratinocyte cell-cell adhesion and ectodermal development.

Lipoid proteinosis maps to 1q21 and is caused by mutations in the extracellular matrix protein 1 gene (ECM1)

Lipoid proteinosis (LP), also known as hyalinosis cutis et mucosae or Urbach-Wiethe disease (OMIM 247100) is a rare, autosomal recessive disorder typified by generalized thickening of skin, mucosae and certain viscera. Classical features include beaded eyelid papules and laryngeal infiltration leading to hoarseness. Histologically, there is widespread deposition of hyaline (glycoprotein) material and disruption/reduplication of basement membrane. The aetiology of LP is currently unknown. Using DNA from three affected siblings in a consanguineous Saudi Arabian family we performed genome-wide linkage and mapped the disorder to 1q21 (marker D1S498) with a two-point LOD score of 3.45 at theta = 0. A further 28 affected individuals from five other unrelated consanguineous family groups from different geographical regions also showed complete linkage and resulted in a maximum two-point LOD score of 21.85 at theta = 0. Using available markers in the interval between D1S442 and D1S305, the observed recombinants placed the gene in a 2.3 cM critical interval between D1S2344 and D1S2343 (Marshfield genetic map) corresponding to an approximately 6.5 Mb region on the UCSC physical map. Using a candidate gene approach (comparison of control versus LP gene expression in cultured fibroblasts) and subsequent direct sequencing of genomic DNA, we identified six different homozygous loss-of-function mutations in the extracellular matrix protein 1 gene (ECM1). Although the precise function of ECM1 is not known, our findings provide the first clinical indication of its relevance to skin adhesion, epidermal differentiation, wound healing, scarring, angiogenesis/angiopathy and basement membrane physiology, as well as defining the molecular basis of this inherited disorder.

EEC (Ectrodactyly, Ectodermal dysplasia, Clefting) syndrome: heterozygous mutation in the p63 gene (R279H) and DNA-based prenatal diagnosis

BACKGROUND

Germline mis-sense mutations in the DNA-binding domain of the p63 gene have recently been established as the molecular basis for the autosomal dominant EEC (Ectrodactyly, Ectodermal dysplasia, Clefting) syndrome.

OBJECTIVES

To examine genomic DNA from a 36-year-old woman, her 58-year-old father and her 11-year-old son, all with the EEC syndrome, to determine the inherent p63 mutation and, after genetic counselling, to use knowledge of the mutation to undertake a first-trimester DNA-based prenatal diagnosis in a subsequent pregnancy.

METHODS

Fetal DNA was extracted from chorionic villi and used to amplify exon 7 of p63 containing the potential mutation. Direct sequencing and restriction endonuclease digestion (loss of AciI site on mutant allele) were used for DNA-based prenatal diagnosis.

RESULTS

We identified a heterozygous arginine to histidine p63 mutation, R279H, in all three affected individuals. Prenatal diagnosis demonstrated a homozygous wild-type sequence predicting an unaffected child: a healthy boy was subsequently born at full-term.

CONCLUSIONS

These data expand the p63 gene mutation database and provide the first example of a DNA-based prenatal test in this ectodermal dysplasia syndrome.

Compound heterozygosity for non-sense and mis-sense mutations in desmoplakin underlies skin fragility/woolly hair syndrome

The constitutive desmosomal plaque protein desmoplakin plays a vital part in keratinocyte adhesion in linking the transmembranous desmosomal cadherins to the cytoplasmic keratin filament network. Recently, mutations in desmoplakin have been shown to underlie some cases of the autosomal dominant disorder, striate palmoplantar keratoderma, as well as an autosomal recessive condition characterized by dilated cardiomyopathy, woolly hair, and keratoderma. Here, we describe two unrelated individuals with a new autosomal recessive genodermatosis characterized by focal and diffuse palmoplantar keratoderma, hyperkeratotic plaques on the trunk and limbs, varying degrees of alopecia, but no apparent cardiac anomalies. Mutation screening of desmoplakin demonstrated compound heterozygosity for a non-sense/mis-sense combination of mutations in both cases, C809X/N287K and Q664X/R2366C, respectively. Heterozygous carriers of any of these mutations displayed no phenotypic abnormalities. Immunohistochemistry of skin biopsies from both affected individuals revealed that desmoplakin was not just located at the cell periphery but there was also cytoplasmic staining. In addition, electron microscopy demonstrated acantholysis throughout all layers of the skin, focal detachment of desmosomes into the intercellular spaces, and perinuclear condensation of the suprabasal keratin intermediate filament network. Clinicopathologic and mutational analyses therefore demonstrate that desmoplakin haploinsufficiency can be tolerated in some cases, but that in combination with a mis-sense mutation on the other allele, the consequences are a severe genodermatosis with specific clinical manifestations.

Sequential reorganization of cornified cell keratin filaments involving filaggrin-mediated compaction and keratin 1 deimination

The final step of keratinocyte differentiation, transition from the granular cells to the cornified cells, involves various post-translational modifications that include deimination of arginine residues. Major deiminated epidermal proteins are derived from K1. Two preferred deimination sites were identified in mouse K1, one in the V1 and the other in the V2 subdomains. An antibody against the deiminated peptide sequence in the V2 subdomain recognized not only deiminated mouse K1 but also deiminated human K1. In this study we analyzed distribution of deiminated K1 in normal human skin and in bullous congenital ichthyosiform erythroderma at light and electron microscopic levels. In normal skin the first few (1-3) cornified cell layers were positive for filaggrin and negative for the antibody against deiminated mouse K1 peptide, whereas the more superficial cells were negative for filaggrin and strongly positive for the antibody against deiminated mouse K1 peptide, indicating slightly delayed onset of K1 deimination at the initial stage of cornification. The clumped keratin in bullous congenital ichthyosiform erythroderma that was not properly compacted with filaggrin was poorly positive to the antibody against deiminated mouse K1 peptide. In addition, K1 derivatives in bullous congenital ichthyosiform erythroderma reacted poorly with the antibody against deiminated mouse K1 peptide compared with the normal control in immunoblot analyses. Our results suggest sequential reorganization of cornified cell keratin filaments involving filaggrin-mediated compaction and K1 deimination. Abnormal keratin aggregation in bullous congenital ichthyosiform erythroderma is likely to disturb the normal deimination of K1.