The cytoplasmic plaque protein desmoplakin (DP), which is located in desmosomes, plays a major role in epithelial and muscle cell adhesion by linking the transmembrane cadherins to the cytoplasmic intermediate filament network. Mutations of DP may cause striate palmoplantar keratoderma, arrhythmogenic right ventricular dysplasia, skin fragility/woolly hair syndrome, Naxos-like disease, and Carvajal syndrome. DP must be indispensable, because DP-/- mice are early abortive. Here, we report a patient with severe fragility of skin and mucous membranes caused by genetic truncation of the DP tail. The new phenotype is lethal in the neonatal period because of immense transcutaneous fluid loss. The phenotype also comprised universal alopecia, neonatal teeth, and nail loss. Histology showed suprabasal clefting and acantholysis throughout the spinous layer, mimicking pemphigus. Electron microscopy revealed disconnection of keratin intermediate filaments from desmosomes. Immunofluorescence staining of DP showed a distinct punctate intercellular pattern in the patient's skin. Protein analysis revealed expression of truncated DP polypeptides. Mutational analysis of the patient demonstrated compound heterozygosity for two DP mutations, 6079C-->T (R1934X) and 6370delTT, respectively. Aberrant mRNA transcripts that predict premature termination of translation with loss of the three intermediate filament-binding subdomains in the DP tail were detected by RT-PCR. The new dramatic phenotype, which we named "lethal acantholytic epidermolysis bullosa," underscores the paramount role of DP in epidermal integrity.

Circulating IgG from a large subset of bullous pemphigoid (BP) patients reacted on immunoblot with a 120-kDa protein in conditioned keratinocyte culture medium and in keratinocyte cell extracts. A protein with a similar molecular weight was recognized by circulating IgA from a subset of patients with linear IgA dermatosis (LAD). Both affinity-purified 120-kDa-specific BP IgG and 120-kDa-specific LAD IgA bound to the roof of salt-split skin. Both proteins recognized are collagenous glycoproteins. Deglycosylation with N-glycosidase F resulted in an identical reduction in molecular weight for both the BP-IgG-recognized protein and the LAD-IgA-recognized protein. Both proteins were equally susceptible to digestion with type VII collagenase. Furthermore, both proteins were absent from conditioned culture medium of keratinocytes from patients with BP180-deficient general atrophic benign epidermolysis bullosa (GABEB). Immunodepletion studies showed that the 120-kDa LAD antigen could be removed from conditioned culture medium by anti-120-kDa BP IgG. Thus these results indicate that these proteins are either highly related or, most probably, identical. A strong antigenic relationship between the 120-kDa protein and the 180-kDa bullous pemphigoid antigen (BP180) was detected by cross-reaction of affinity-purified anti-120-kDa BP patient antibodies to BP180 and cross-reaction of monoclonal anti-180-kDa antibodies to the 120-kDa protein. Notwithstanding this cross-reactivity, the 120-kDa protein also exhibits unique epitopes demonstrated by the nonreactivity of individual anti-120-kDa BP and LAD patient serum with the 180-kDa antigen.

We studied a kindred with recessive epidermolysis bullosa simplex in which the affected members lacked expression of the basal cell keratin 14. The patients had severe generalized skin blistering that improved slightly with age. The basal cells of the patients did not express keratin 14 and contained no keratin intermediate filaments. The expression of keratin 5, the obligate copolymer of keratin 14, was slightly reduced. The expression of keratin 15, the alternative basal cell keratin, was increased, suggesting upregulation or stabilization to compensate for the lack of keratin 14. The expression of keratin 16, keratin 17, and keratin 19 in the patient's skin was not different from controls. Immunoelectron microscopy showed a loose network of keratin 5/keratin 15 protofilaments in the basal cells. Keratin 15 filaments did not aggregate into higher order bundles. Sequence analysis of genomic DNA revealed a homozygous mutation in the 3'-acceptor splice site of intron 1 (1840 A-->C) in the affected individuals. This mutation led to the skipping of exon 2 in 24% of the KRT14 transcripts and to the use of a cryptic splice site in 76% of the transcripts. Premature termination codons were generated in all transcripts (codons 175+1 or 175+29), leading to a truncated keratin 14 protein within the helical 1B rod domain. The disorder was associated with circumscribed hyperkeratotic lesions with the histology of epidermolytic hyperkeratosis. The prognosis of keratin 14 ablation is much better in the human than in the mouse.

IntroductionGeneralized atrophic benign epidermolysis bullosa (GA-BEB) is a form of nonlethal junctional epidermolysis bullosa characterized by universal alopecia and atrophy of the skin. We report a deficiency of the 180-kD bullous pemphigoid antigen in three patients with GABEB from unrelated families. We screened specimens of clinically normal skin from nine junctional epidermolysis bullosa patients (3 GABEB, 4 lethal, 1 cicatricial, 1 pretibial) by immunofluorescence using monoclonal antibodies to the 180-kD and 230-kD bullous pemphigoid antigens (BP180 and BP230). In the skin of the three GABEB patients there was no reactivity with antibodies to BP180, whereas staining for BP230 was normal. In the skin of the other six, non-GABEB patients, included in this study the expression of BP180 and BP230 was normal. Immunoblot analysis of cultured keratinocytes from one of the GABEB patients also failed to detect BP180 antigen, whereas BP230 was present in normal amounts. In previous studies on the expression of the bullous pemphigoid antigen in JEB, sera from bullous pemphigoid (BP) patients were used, the specificity of which had not been analyzed by immunoblotting (6-9). The expression was found to be normal or variable. Later it became apparent that BP-serum is a mixture of polyclonal antibodies, which are very difficult to characterize, even after affinity-purification (10). Fortunately, reliable monospecific antibodies for each of the two major bullous pemphigoid antigens have now become available (1 1, 12).In this study we used monoclonal antibodies specific for BPI 80 and BP230 (11,12). In addition we studied the expression of the newly described 500-kD hemidesmosomal plaque protein HD1 (13)

Revertant mosaicism due to in vivo reversion of an inherited mutation has been described in the genetic skin disease epidermolysis bullosa (EB) for the genes KRT14 and COL17A1. Here we demonstrate the presence of multiple second-site mutations, all correcting the germline mutation LAMB3:c.628G→A;p.E210K, in 2 unrelated non-Herlitz junctional EB patients with revertant mosaicism. Both probands had a severe reduction in laminin-332 expression in their affected skin. Remarkably, the skin on the lower leg of patient 078-01 (c.628G→A/c.1903C→T) became progressively clinically healthy, with normal expression of laminin-332 on previously affected skin. In the other proband, 029-01 (c.628G→A/c.628G→A), the revertant patches were located at his arms, shoulder, and chest. DNA analysis showed different second-site mutations in revertant keratinocytes of distinct biopsy specimens (c.565-3T→C, c.596G→C;p.G199A, c.619A→C;p.K207Q, c.628+42G→A, and c.629-1G→A), implying that there is not a single preferred mechanism for the correction of a specific mutation. Our data offer prospects for EB treatment in particular cases, since revertant mosaicism seems to occur at a higher frequency than expected. This opens the possibility of applying revertant cell therapy in mosaic EB of the LAMB3 gene by using autologous naturally corrected keratinocytes, thereby bypassing the recombinant gene correction phase. IntroductionReverse mutations in germline or somatic cells bearing an inherited disease-causing mutation can change the phenotype from affected to normal by reexpression of the involved protein. These reverse mutations can be true back mutations -leading to the original wild-type sequence and thus wild-type protein -or can be additional second-site mutations that compensate for the effect of the primary inherited mutation (1). In the latter case, small changes in the amino acid sequence may occur. Revertant mosaicism has been demonstrated for different genetic diseases and in different cell types, as in hepatocytes, lymphocytes, and, in the case of epidermolysis bullosa (EB), keratinocytes (reviewed in refs. 2, 3). EB is a clinically heterogeneous group of heritable blistering disorders leading to fragility of the skin and mucous membranes. The subgroup junctional EB (JEB), characterized by separation at the lamina lucida of the epidermal basement membrane zone (BMZ), is caused by recessive mutations in the genes encoding type XVII collagen (COL17A1), integrin α6β4 (ITGA6 and ITGB4), or laminin-332 (LM-332; LAMA3, LAMB3, and LAMC2) (4). Recently, the first instance of correction of EB skin by transplantation of genetically modified epidermal stem cells was reported for a compound heterozygous carrier of laminin β3 (LAMB3) mutations (5).Revertant mosaicism in EB due to in vivo reversion of somatic cells has been described for the genes COL17A1 and KRT14 (6-10). The first reported case involved the reversion of one of the defective COL17A1 alleles into a wild-type sequence due to a mitotic gene conversion event (6). In a second EB patie...

Revertant mosaicism by somatic reversion of inherited mutations has been described for a number of genetic diseases. Several mechanisms can underlie this reversion process, such as gene conversion, crossing-over, true back mutation, and second-site mutation. Here, we report the occurrence of multiple corrections in two unrelated probands with revertant mosaicism of non-Herlitz junctional epidermolysis bullosa, an autosomal recessive genodermatosis due to mutations in the COL17A1 gene. Immunofluorescence microscopy and laser dissection microscopy, followed by DNA and RNA analysis, were performed on skin biopsy specimens. In patient 1, a true back mutation, 3781T-->C, was identified in the specimen from the arm, and a second-site mutation, 4463-1G-->A, which compensated for the frameshift caused by the inherited 4424-5insC mutation, was identified in the 3' splice site of exon 55 in a specimen from the middle finger. Patient 2 showed--besides two distinct gene conversion events in specimens from the arm and hand sites, both of which corrected the 1706delA mutation--a second-site mutation (3782G-->C) in an ankle specimen, which prevented the premature ending of the protein by the 3781C-->T nonsense mutation (R1226X). Thus, both inherited mutations, paternal as well as maternal, reverted at least once by different reversion events in distinct cell clusters in the described patients. The occurrence of multiple correcting mutations within the same patient indicates that in vivo reversion is less unusual than was generally thought. Furthermore, in the male patient, mosaic patterns of type XVII collagen-positive keratinocytes were present in clinically unaffected and affected skin. This latter observation makes it likely that reversion may be overlooked and may happen more often than expected.

Autoantibodies against the 3 desmocollin (Dsc; Dsc1-Dsc3) isoforms have been described in different pemphigus variants. Here, we developed state-of-the-art detection systems for serum anti-Dsc1, Dsc2and Dsc1 IgG and IgA. These assays were applied in 5 different cohorts including pemphigus vulgaris (PV) patients with compatible direct immunofluorescence (IF) microscopy but no reactivity against desmogleins 1 and 3 (n = 24) and sera from patients with autoimmune blistering diseases with positive direct IF microscopy taken at the time of diagnosis (n = 749). We found that detection of anti-Dsc serum reactivity is not helpful in the routine diagnosis of PV, pemphigus foliaceus and paraneoplastic pemphigus but may be valuable in pemphigus vegetans. | BACKGROUNDDesmocollins (Dsc) and desmogleins (Dsg) belong to the Ca 2+ -dependent cadherin adhesion protein family. They are part of the desmosomes and provide proper cohesion between neighbouring cells of various tissues including skin and surface-close epithelia.[1] The 4 Dsg (Dsg1-Dsg4) and 3 Dsc (Dsc1-Dsc3) isoforms share a similar architecture with approximately 30% sequence identity ( Figure 1A). By both homo-and heterophilic transinteraction of the outmost extracellular N-termini and binding to proteins of the desmosomal plaque, Dsc and Dsg mediate connection between the intermediate filaments of neighbouring cells.[1]In pemphigus vulgaris (PV), the major target antigen is Dsg3. [2,3] In patients with the mucocutaneous phenotype of PV, autoantibodies against Dsg1 in addition to Dsg3 reactivity are found. [2,3] In contrast, autoantibody reactivity in paraneoplastic pemphigus (PNP) is more diverse. In addition to antibodies against Dsg3, reactivity against proteins of the plakin family comprising desmoplakins I and II, periplakin, envoplakin, plectin, and BP230 as well as Dsg1, and, more recently, α2-macroglobulin-like 1 and epiplakin has been described. [4,5] Autoantibodies against all 3 Dsc isoforms have been reported in various pemphigus subtypes including PV, pemphigus foliaceus, pemphigus vegetans, pemphigus herpetiformis, IgA pemphigus and PNP. [6][7][8][9] A pathogenic relevance of anti-Dsc antibodies has been suggested by different in vitro models based on the incubation of cultured human keratinocytes and human skin with anti-Dsc3 IgG. These data are supported by the finding of intra-epidermal splitting resulting in erosions and hair loss in mice with Dsc3-null skin. | QUESTIONS ADDRESSEDWhile Dsc1 has been identified as major target antigen in the subcorneal pustular dermatosis type of IgA pemphigus, [18] the diagnostic value of detecting serum anti-Dsc antibodies in PV is still unclear. | EXPERIMENTAL DESIGNTo address this open question, we cloned and expressed the ectodo- This strategy has recently led to highly sensitive and specific test systems for serum autoantibodies against Dsg1, Dsg3, BP230 and the NC1 domain of type VII collagen.To evaluate the diagnostic relevance of detecting anti-Dsc antibodies in pemphigus sera, 5 distinct cohorts we...

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