Epidermolysis bullosa simplex with muscular dystrophy. Review of the literature and a case report.

Epidermolysis Bullosa Simplex Associated with Severe Mucous Membrane Involvement and Novel Mutations in the Plectin Gene

Epidermolysis bullosa simplex associated with muscular dystrophy: Phenotype-genotype correlations and review of the literature

Plectin, a giant multifunctional cytolinker protein, plays a crucial role in stabilizing and orchestrating intermediate filament networks in cells. Mutations in the human plectin gene result in multiple diseases manifesting with muscular dystrophy, skin blistering, and signs of neuropathy. The most common disease caused by plectin deficiency is epidermolysis bullosa simplex (EBS)-MD, a rare autosomal-recessive skin blistering disorder with late-onset muscular dystrophy. EBS-MD patients and plectin-deficient mice display pathologic desmin-positive protein aggregates, degenerated myofibrils, and mitochondrial abnormalities, the hallmarks of myofibrillar myopathies. In addition to EBS-MD, plectin mutations have been shown to cause EBS-MD with a myasthenic syndrome, limb-girdle muscular dystrophy type 2Q, EBS with pyloric atresia, and EBS-Ogna. This review focuses on clinical and pathological manifestations of these plectinopathies. It addresses especially plectin's role in skeletal muscle, where a loss of muscle fiber integrity and profound changes of myofiber cytoarchitecture are observed in its absence. Furthermore, the highly complex genetic and molecular structure of plectin is discussed; a high number of differentially spliced exons give rise to a variety of different isoforms, which fulfill distinct functions in different cell types and tissues. Plectin's abilities to act as a dynamic organizer of intermediate filament networks and to interact with a multitude of different interaction partners are the basis for its function as a scaffolding platform for proteins involved in signaling. Finally, the article addresses a series of genetically manipulated mouse lines that were generated to serve as powerful models to study functional and molecular consequences of plectin gene defects.

Epidermolysis Bullosa Simplex Associated with Pyloric Atresia Is a Novel Clinical Subtype Caused by Mutations in the Plectin Gene ( PLEC1)

Epidermolysis bullosa (EB) is a very heterogeneous hereditary disease of the skin and mucous membranes, characterized by erosions and blistering after minor traumatization. Up to now at least 12 genes are known to underlie EB, which render structural and mechanical stability of the skin (Fine et al., 2008). The characteristic blister formation occurs on the level of the basement membrane zone and the basal keratinocytes, depending on the gene, which is mutated. In EB simplex (EBS) the split formation in the skin occurs due to cytolysis of the basal keratinocytes, in junctional EB (JEB) within the lamina lucida and in dystrophic EB (DEB) on the dermal aspect of the basement membrane zone. Due to the clinical and genetic heterogeneity of this disease the development of a gene therapy is challenging, since every type of EB has to be targeted separately. Furthermore, the different subtypes differ in their mode of inheritance. Especially for basal EB simplex, where mutations in the keratin 5 (K5), keratin 14 (K14) and plectin (PLEC) genes may cause the clinical phenotype, dominant mutations are frequent. But also in dystrophic EB, where mutations in the collagen VII gene (COL7A1) are causative for the disease, dominantly inherited subtypes are known. Another characteristic feature of the involved genes is that many of them are very large and exceed the packaging capacities of commonly used (viral) vectors (e.g. COL7A1: ~9,3kb, PLEC: ~14.8kb). Functionally, all genes involved in EB have structural significance. Whereas keratin 5 and keratin 14 are major components of the cytoskeleton in basal keratinocytes, plectin is a cytolinker protein, connecting the actin filament network with the microtubules, the intermediate filaments and the hemidesmosomes and desmosomes. Isoforms of plectin are expressed in many cell types and always have “networking” functions. This is the reason why epidermolysis bullosa triggered by mutations in this gene goes along with muscular dystrophy and pyloric atresia. 12 plectin isoforms, differing in their 5’ transcript portion have been identified up to now, most of them differing in their first exon. However, the structure and mode of function is comparable between all isoforms (Rezniczek et al., 2003). Structurally, plectin consists of two globular domains, flanking a central rod domain. The 5’ globular domain is encoded by exons 1 to 30 and is over 4kb in length, whereas the rod is encoded by one single 3.38kb

Epidermolysis bullosa simplex with muscular dystrophy (OMIM 226670) is an autosomal recessive disorder caused by mutations of the human plectin gene on chromosome 8q24. Here, we report a 3-year-old girl, offspring of a consanguineous Lebanese family, who presented with skin blistering and recurrent episodes of severe respiratory distress necessitating tracheotomy at the age of 2 years. Repeated examination did not provide any evidence of muscle involvement. Indirect immunofluorescence analysis of a diagnostic skin biopsy with four different domain specific plectin antibodies showed a complete absence of plectin staining. Mutation analysis revealed a novel homozygous single guanine insertion mutation (5588insG/5588insG) residing in the N-terminal part of exon 31 of the plectin gene. The complete lack of protein expression, which may be attributed to a nonsense-mediated plectin mRNA decay, is likely to cause muscular dystrophy and other multisystem involvement later in life.

G.P.24 Congenital muscular dystrophy with epidermolysis bullosa: A case report

Epidermolysis Bullosa: Novel and De Novo Premature Termination Codon and Deletion Mutations in the Plectin Gene Predict Late-Onset Muscular Dystrophy

Respiratory tract involvement in a child with epidermolysis bullosa simplex with plectin deficiency: A case report

Genetic diseases affecting the epidermis

P.48 - Novel compound heterozygous mutations in PLEC gene causing epidermolysis bullosa simplex with muscular dystrophy, case series of two affected sisters

Mutations in the plectin gene (PLEC1) cause epidermolysis bullosa simplex (EBS), which may associate with muscular dystrophy (EBS-MD) or pyloric atresia (EBS-PA). The association of EBS with congenital myasthenic syndrome (CMS) is also suspected to result from PLEC1 mutations. We report here a consanguineous patient with EBS and CMS for whom mutational analysis of PLEC1 revealed a homozygous 36 nucleotide insertion (1506_1507ins36) that results in a reduced expression of PLEC1 mRNA and plectin in the patient muscle. In addition, mutational analysis of CHRNE revealed a homozygous 1293insG, which is a well-known low-expressor receptor mutation. A skin biopsy revealed signs of EBS, and an anconeus muscle biopsy showed signs of a mild myopathy. Endplate studies showed fragmentation of endplates, postsynaptic simplification, and large collections of thread-like mitochondria. Amplitudes of miniature endplate potentials were diminished, but the endplate quantal content was actually increased. The complex phenotype presented here results from mutations in two separate genes. While the skin manifestations are because of the PLEC1 mutation, footprints of mutations in PLEC1 and CHRNE are present at the neuromuscular junction of the patient indicating that abnormalities in both genes contribute to the CMS phenotype.

Plectin, a versatile 500-kDa cytolinker protein, is essential for muscle fiber integrity and function. The most common disease caused by mutations in the human plectin gene, epidermolysis bullosa simplex with muscular dystrophy (EBS-MD), is characterized by severe skin blistering and progressive muscular dystrophy. Besides displaying pathological desmin-positive protein aggregates and degenerative changes in the myofibrillar apparatus, skeletal muscle specimens of EBS-MD patients and plectin-deficient mice are characterized by massive mitochondrial alterations. In this study, we demonstrate that structural and functional alterations of mitochondria are a primary aftermath of plectin deficiency in muscle, contributing to myofiber degeneration. We found that in skeletal muscle of conditional plectin knockout mice (MCK-Cre/cKO), mitochondrial content was reduced, and mitochondria were aggregated in sarcoplasmic and subsarcolemmal regions and were no longer associated with Z-disks. Additionally, decreased mitochondrial citrate synthase activity, respiratory function and altered adenosine diphosphate kinetics were characteristic of plectin-deficient muscles. To analyze a mechanistic link between plectin deficiency and mitochondrial alterations, we comparatively assessed mitochondrial morphology and function in whole muscle and teased muscle fibers of wild-type, MCK-Cre/cKO and plectin isoform-specific knockout mice that were lacking just one isoform (either P1b or P1d) while expressing all others. Monitoring morphological alterations of mitochondria, an isoform P1b-specific phenotype affecting the mitochondrial fusion–fission machinery and manifesting with upregulated mitochondrial fusion-associated protein mitofusin-2 could be identified. Our results show that the depletion of distinct plectin isoforms affects mitochondrial network organization and function in different ways.

Plectinopathy-associated disorders are caused by mutations in the PLECTIN (PLEC) gene encoding Plectin protein. PLEC mutations cause a spectrum of diseases defined by varying degrees of signs, mostly with epidermolysis bullosa simplex with muscular dystrophy (EBS-MD) and plectinopathy-related disorder is limb-girdle muscular dystrophy type 2Q (LGMD2Q). Here we report three cases with EBS-MD and LGMD2Q disorders analyzed by exome sequencing followed by mutation confirmation. A complete clinical examination was done by expert specialists and clinical geneticists in Next Generation Genetic polyclinic, Mashhad, Iran (NGC, years 2020_2021),. Genomic DNA was extracted and evaluated through whole-exome sequencing analysis followed by Sanger sequencing for co-segregation analysis of PLEC candidate variants. We found three cases with the plectinopathy-related disease, two patients with limb-girdle muscular dystrophy type 2Q (LGMD2Q), and the other affected proband suffers from epidermolysis bullosa simplex combined with muscular dystrophy (EBS-MD) with variable zygosity mutations for PLEC. Motor development disorder and muscular dystrophy symptoms have different age onset in affected individuals. Patients with EBS demonstrated symptoms such as blistering, skin scars, neonatal-onset, and nail dystrophy. We report plectinopathy-associated disorders to expand clinical phenotypes in different types of PLEC-related diseases. We suppose to design more well-organized research based on comprehensive knowledge about the genetic basis of plectinopathy diseases.

Plectin, a highly versatile and multifunctional cytolinker, has been implicated in several multisystemic disorders. Most sequence variations in the human plectin gene (PLEC) cause epidermolysis bullosa simplex with muscular dystrophy (EBS-MD), an autosomal recessive skin-blistering disorder associated with progressive muscle weakness. In this study, we performed a comprehensive cell biological analysis of dermal fibroblasts from three different patients with EBS-MD, where PLEC expression analyses revealed preserved mRNA levels in all cases, whereas full-length plectin protein content was significantly reduced or completely absent. Downstream effects of pathogenic PLEC sequence alterations included massive bundling of vimentin intermediate filament networks, including the occurrence of ring-like nuclei-encasing filament bundles, elongated mitochondrial networks, and abnormal nuclear morphologies. We found that essential fibroblast functions such as wound healing, migration, or orientation upon cyclic stretch were significantly impaired in the cells of patients with EBS-MD. Finally, EBS-MD fibroblasts displayed reduced adhesion capacities, which could be attributed to smaller focal adhesion contacts. Our study not only emphasizes plectin's functional role in human skin fibroblasts, it also provides further insights into the understanding of EBS-MD-associated disease mechanisms.