Report of a patient with limb-girdle muscular dystrophy, ptosis and ophthalmoparesis caused by plectinopathy

Muscle-Related Plectinopathies

Plectin is a giant cytoskeletal crosslinker and intermediate filament stabilizing protein. Mutations in the human plectin gene (PLEC) cause several rare diseases that are grouped under the term plectinopathies. The most common disorder is autosomal recessive disease epidermolysis bullosa simplex with muscular dystrophy (EBS-MD), which is characterized by skin blistering and progressive muscle weakness. Besides EBS-MD, PLEC mutations lead to EBS with nail dystrophy, EBS-MD with a myasthenic syndrome, EBS with pyloric atresia, limb-girdle muscular dystrophy type R17, or EBS-Ogna. In this review, we focus on the clinical and pathological manifestations caused by PLEC mutations on skeletal and cardiac muscle. Skeletal muscle biopsies from EBS-MD patients and plectin-deficient mice revealed severe dystrophic features with variation in fiber size, degenerative myofibrillar changes, mitochondrial alterations, and pathological desmin-positive protein aggregates. Ultrastructurally, PLEC mutations lead to a disorganization of myofibrils and sarcomeres, Z- and I-band alterations, autophagic vacuoles and cytoplasmic bodies, and misplaced and degenerating mitochondria. We also summarize a variety of genetically manipulated mouse and cell models, which are either plectin-deficient or that specifically lack a skeletal muscle-expressed plectin isoform. These models are powerful tools to study functional and molecular consequences of PLEC defects and their downstream effects on the skeletal muscle organization.

Four Individuals with a Homozygous Mutation in Exon 1f of the PLEC Gene and Associated Myasthenic Features

We identified the known c.1_9del mutation in the PLEC gene in four unrelated females from consanguineous families of Turkish origin. All individuals presented with slowly progressive limb-girdle weakness without any dermatological findings, and dystrophic changes observed in their muscle biopsies. Additionally, the neurological examination revealed ptosis, facial weakness, fatigability, and muscle cramps in all four cases. In two patients, repetitive nerve stimulation showed a borderline decrement and a high jitter was detected in all patients by single-fiber electromyography. Clinical improvement was observed after treatment with pyridostigmine and salbutamol was started. We further characterize the phenotype of patients with limb-girdle muscular dystrophy R17 clinically, by muscle magnetic resonance imaging (MRI) features and by describing a common 3.8 Mb haplotype in three individuals from the same geographical region. In addition, we review the neuromuscular symptoms associated with PLEC mutations and the role of plectin in the neuromuscular junction.

Clinical, pathological, imaging, and genetic characterization in a Taiwanese cohort with limb-girdle muscular dystrophy

Background

Limb-girdle muscular dystrophy (LGMD) is a genetically heterogeneous, hereditary disease characterized by limb-girdle weakness and histologically dystrophic changes. The prevalence of each subtype of LGMD varies among different ethnic populations. This study for the first time analyzed the phenotypes and genotypes in Taiwanese patients with LGMD in a referral center for neuromuscular diseases (NMDs).

Results

We enrolled 102 patients clinically suspected of having LGMD who underwent muscle biopsy with subsequent genetic analysis in the previous 10 years. On the basis of different pathological categories, we performed sequencing of target genes or panel for NMDs and then identified patients with type 1B, 1E, 2A, 2B, 2D, 2I, 2G, 2 N, and 2Q. The 1B patients with LMNA mutation presented with mild limb-girdle weakness but no conduction defect at the time. All 1E patients with DES mutation exhibited predominantly proximal weakness along with distal weakness. In our cohort, 2B and 2I were the most frequent forms of LGMD; several common or founder mutations were identified, including c.1097_1099delACA (p.Asn366del) in DES, homozygous c.101G > T (p.Arg34Leu) in SGCA, homozygous c.26_33dup (p.Glu12Argfs*20) in TCAP, c.545A > G (p.Tyr182Cys), and c.948delC (p.Cys317Alafs*111) in FKRP. Clinically, the prevalence of dilated cardiomyopathy in our patients with LGMD2I aged > 18 years was 100%, much higher than that in European cohorts. The only patient with LGMD2Q with PLEC mutation did not exhibit skin lesions or gastrointestinal abnormalities but had mild facial weakness. Muscle imaging of LGMD1E and 2G revealed a more uniform involvement than did other LGMD types.

Conclusion

Our study revealed that detailed clinical manifestation together with muscle pathology and imaging remain critical in guiding further molecular analyses and are crucial for establishing genotype–phenotype correlations. We also determined the common mutations and prevalence for different subtypes of LGMD in our cohort, which could be useful when providing specific care and personalized therapy to patients with LGMD.

Glu20Ter Variant in PLEC 1f Isoform Causes Limb-Girdle Muscle Dystrophy with Lung Injury

Plectinopathies are orphan diseases caused by PLEC gene mutations. PLEC is encoding the protein plectin, playing a role in linking cytoskeleton components in various tissues. In this study, we describe the clinical case of a 26-year-old patient with an early onset plectinopathy variant “limb-girdle muscle dystrophy type 2Q,” report histopathological and ultrastructural findings in m. vastus lateralis biopsy and a novel homozygous likely pathogenic variant (NM_201378.3:c.58G>T, NP_958780.1:p.Glu20Ter) in isoform 1f of the gene PLEC. The patient had an early childhood onset with retarded physical development, moderate weakness in pelvic girdle muscles, progressive weakening of limb-girdle muscles after the age of 21, pronounced atrophy of axial muscles, and hypertrophy of the gastrocnemius, deltoid, and triceps muscles, intermittent dyspnea, and no skin involvement. Findings included: non-infectious bronchiolitis and atelectasis signs, biopsy revealed myodystrophal pattern without macrophage infiltration, muscle fiber cytoskeleton disorganization resulted from the plectin loss, incomplete reparative rhabdomyogenesis, and moderate endomysial fibrosis. We have determined a novel likely pathogenic variant in PLEC 1f isoform that causes limb-girdle muscle dystrophy type 2Q and described the third case concerning an isolated myodystrophic phenotype of LGMD2Q with the likely pathogenic variant in PLEC 1f isoform. In addition, we have demonstrated the presence of severe lung injury in a patient and his siblings with the same myodystrophic phenotype and discussed the possible role of plectin deficiency in its pathogenesis.