The dystonin gene (DST) encodes three major isoforms, DST-a, DST-b and DST-e. Biallelic pathogenic variants in DST have previously been associated with two allelic monogenic disorders: hereditary sensory and autonomic neuropathy type VI (caused by a loss of DST-a) and epidermolysis bullosa simplex 3 (caused by a loss of DST-e). We investigated patients diagnosed with congenital myopathy using exome or genome sequencing. In 19 affected individuals from 14 unrelated families, we identified nine different variants in biallelic state located in exons 40-41, specific to DST-b. Affected individuals presented with severe neonatal myopathy characterized by arthrogryposis, hypotonia and dilated cardiomyopathy. Postnatal CPAP ventilation was required in nine patients, and seven died within the first three years of life. Survivors showed an improvement of symptoms, with the oldest three patients, now over 25 years old, exhibiting normal cognition and being ambulatory. RNA analyses demonstrated that transcripts encoding DST-b are predominantly expressed in skeletal muscle, heart tissue and cultured fibroblasts, but not in brain, matching the phenotypic spectrum. Patient-derived fibroblasts exhibited reduced DST mRNA expression. Proteomic analysis confirmed a reduction of DST protein levels due to an absence of the DST-b isoform. Muscle biopsies from four patients aged 1 month to 3 years revealed mild, non-specific myopathic changes. Ultrastructural analysis in three individuals showed mild and focal myofibrillar disruption and non-specific undulating nuclear membranes, with these changes observed in two cases each. Additionally, we identified two homozygous variants affecting both DST-a and DST-b isoforms in four patients from two unrelated families; all presented with severe arthrogryposis and died intrauterine or shortly after birth. Genotype-phenotype correlation in these patients and previously published cases with respective variants resulted in the definition of a DST-associated lethal congenital contracture syndrome. Our findings demonstrate that biallelic variants exclusively affecting DST-b cause an autosomal recessive congenital myopathy. Variants that also impact DST-a besides DST-b result in a more severe, lethal congenital contracture syndrome. The location of the variant within DST allows for phenotype prediction. We propose redefining DST as a disease-associated gene linked to four distinct allelic disease phenotypes.

Airway involvement in epidermolysis bullosa (EB) is rare and most commonly associated with junctional EB. Laryngotracheal disease in epidermolysis bullosa simplex (EBS), particularly PLEC (Plectin gene)-related variants, is uncommon but may cause significant morbidity. We report a 7-year-old girl with autosomal recessive PLEC-related EBS who developed progressive supraglottic and glottic stenosis. She presented at 8 months old with severe respiratory distress requiring emergent tracheostomy. Serial endoscopies revealed persistent supraglottic granulation, an anterior glottic web, posterior glottic stenosis, and occasional bullae near the carina, with a patent subglottis and distal trachea. She underwent multiple direct laryngobronchoscopies for cold web release, dilation, mitomycin-C application, Kenacort injection, and excision of suprastomal granulation. Despite clinical stabilization, she remains tracheostomy-dependent with ongoing evaluation for potential decannulation. This case highlights the potential for significant airway disease in PLEC-related EBS, and underscores the importance of early recognition, gentle airway handling, and multidisciplinary management.

Epidermolysis bullosa simplex (EBS), the most common type of EB, is characterized by skin fragility and blister formation within the basal epidermal layer. Most cases are due to autosomal dominant mutations in the keratin genes, KRT5 and KRT14. However, mutations in different genes are responsible for other EBS subtypes. We describe the clinical and molecular features of the first Italian child with autosomal recessive localized EBS due to mutations in the DST gene, encoding the BP230/BPAG1-e protein of hemidesmosomes. Molecular genetic analysis identified compound heterozygous DST nonsense variants, allowing the exclusion of a sporadic case of dominant EBS due to a de novo KRT5/KRT14 mutation. A literature review retrieved members from 20 families from Middle Eastern and South Asian countries presenting with DST-mutated EBS. In addition to illustrating the clinical features of this EBS variant, our case shows the relevance of genetic diagnosis to distinguish EBS subtypes due to different inheritance modes, thereby providing families with appropriate genetic counseling. Epidermolysis bullosa (EB) defines a prototypic group of rare, inherited dermatoses, characteristically featuring skin fragility secondary to structural defects in the dermo-epidermal junction. This skin fragility creates an impaired tolerance to mechanical stress. Trivial mechanical trauma and shear stress can provoke skin blistering, erosions, and ulceration. This places patients with certain forms of epidermolysis bullosa at a greater risk of infection, disabling deformities secondary to heavy scarring, and aggressive cutaneous malignancy, leading to early fatality in some cases. An extensive phenotypic range is described, ranging from fragility and blistering localized to areas of weight-bearing or pressure to widespread generalized involvement, including extracutaneous disease. Thus, certain subtypes of EB confer high morbidity, with a risk of increased mortality due to multi-system pathology. Sixteen genes have been implicated in underpinning at least 30 observed epidermolysis bullosa subtypes. Each subtype features varying phenotypic severity and impact on morbidity and mortality. These subtypes have been organized into 4 major groups based on the ultrastructural plane within the dermo-epidermal junction that the defect impacts: Epidermolysis Bullosa Simplex (EBS) comprises around 70% of all epidermolysis bullosa cases and features a fragility defect in the epidermis, mostly inherited in an autosomal dominant pattern.  Junctional Epidermolysis Bullosa (JEB) is an autosomal recessive fragility defect seen specifically within the lamina lucida and makes up around 5% of all epidermolysis bullosa cases. Dystrophic Epidermolysis Bullosa (DEB) represents around 25% of all epidermolysis bullosa cases and may be autosomal dominant or recessive. Dystrophic epidermolysis bullosa features a fragility defect below the lamina densa of the basement membrane zone. Kindler Epidermolysis Bullosa (KEB) is the rarest of the 4 major epidermolysis bullosa types inherited in an autosomal recessive pattern. The kindlin-1 protein is affected in Kindler epidermolysis bullosa, resulting in fragility in any plane of the dermo-epidermal junction. Around 400 cases have been reported worldwide. Inherited epidermolysis bullosa is distinct from epidermolysis bullosa aquisita, a separate, non-inherited, immunobullous disorder characterized by antibodies against type VII collagen.

Plectin, a multifunctional cytolinker and intermediate filament stabilizing protein, is essential for muscle fibre integrity and function. Mutations in the human plectin gene (PLEC) cause autosomal recessive epidermolysis bullosa simplex with muscular dystrophy (EBS-MD). The disorganization and aggregation of desmin filaments in conjunction with degenerative changes of the myofibrillar apparatus are key features in the skeletal muscle pathology of EBS-MD. We performed a comprehensive analysis addressing protein homeostasis in this rare protein aggregation disease by using human EBS-MD tissue, plectin knock-out mice and plectin-deficient cells. Protein degradation pathways were analysed in muscles from EBS-MD patients, muscle-specific conditional plectin knockout (MCK-Cre/cKO) mice, as well as in plectin-deficient (Plec-/-) myoblasts by electron and immunofluorescence microscopy. To obtain a comprehensive picture of autophagic processes, we evaluated the transcriptional regulation and expression levels of autophagic markers in plectin-deficient muscles and myoblasts (RNA-Seq, qRT-PCR, immunoblotting). Autophagic turnover was dynamically assessed by measuring baseline autophagy as well as specific inhibition and activation in mCherry-EGFP-LC3B-expressing Plec+/+ and Plec-/- myoblasts, and by monitoring primary Plec+/+ and Plec-/- myoblasts using organelle-specific dyes. Wild-type and MCK-Cre/cKO mice were treated with chloroquine or metformin to assess the effects of autophagy inhibition and activation in vivo. Our study identified the accumulation of degradative vacuoles as well as LC3- and SQSTM1-positive patches in EBS-MD patients, MCK-Cre/cKO mouse muscles and Plec-/- myoblasts. The transcriptional regulation of ~30% of autophagy-related genes was altered, and protein levels of downstream targets of the autophagosomal degradation machinery were elevated in MCK-Cre/cKO muscle lysates (e.g., LAMP2, BAG3 and SQSTM1 to ~160, ~150 and ~140% of controls, respectively; p < 0.05). Autophagosome turnover was compromised in mCherry-EGFP-LC3B-expressing Plec-/- myoblasts (~40% reduction in median red:green ratio, reduced puncta number, smaller puncta; p < 0.01). By labelling autophagic compartments with CYTO-ID dye or lysosomes with LYSO-ID, we found reduced signal intensities in primary Plec-/- cells (p < 0.001). Treatment with chloroquine led to drastic swelling of autophagic vacuoles in primary Plec+/+ myoblasts, while the swelling in Plec-/- cells was moderate, establishing a defect in their autophagic clearance. Chloroquine treatment of MCK-Cre/cKO mice corroborated that loss of plectin coincides with impaired autophagic clearance, while metformin amelioratively induced autophagic flux. Our work demonstrates that the characteristic protein aggregation pathology in EBS-MD is linked to an impaired autophagic flux. The obtained results open a new perspective on the understanding of the protein aggregation pathology in plectin-related disorders and provide a basis for further pharmacological intervention.

Plectin (PLEC) is a versatile linker protein expressed in nearly all mammalian tissues, interlinking various components of the cytoskeleton and anchoring the hemidesmosome to the intermediate filament network of basal keratinocytes. Variants in PLEC disrupt its function as a linker protein, resulting in epidermolysis bullosa simplex (EBS), a hereditary skin disorder characterized by blister formation and mechanical fragility. Additionally, EBS patients with PLEC variants often exhibit varying degrees of muscular dystrophy. In this study, we detail the genotype, phenotype, transmission electron microscopy (TEM), and immunofluorescence microscopy (IFM) findings of nine Taiwanese EBS patients with PLEC variants. The patients had 13 pathogenic variants, including two missense variants and one inframe variant. Analyzing muscle involvement, TEM, and IFM findings, we determined that the presence of at least one missense or inframe pathogenic variant was correlated with milder muscular dystrophy or a later onset. Using AlphaFold, we modeled the 3D protein structures to elucidate the structural and functional implications of these pathogenic variants.