Cardiomyopathy diagnosed in the eldest child harbouring p.S24X mutation in JUP

Understanding the molecular basis of cardiomyopathy

Inherited cardiomyopathies are a major cause of mortality and morbidity worldwide and can be caused by mutations in a wide range of proteins located in different cellular compartments. The present review is based on Dr. Ju Chen's 2021 Robert M. Berne Distinguished Lectureship of the American Physiological Society Cardiovascular Section, in which he provided an overview of the current knowledge on the cardiomyopathy-associated proteins that have been studied in his laboratory. The review provides a general summary of the proteins in different compartments of cardiomyocytes associated with cardiomyopathies, with specific focus on the proteins that have been studied in Dr. Chen's laboratory.

Clinical and Molecular Aspects of Naxos Disease

Naxos disease is a recessively inherited pattern of arrhythmogenic cardiomyopathy with palmoplantar keratoderma and woolly hair. The causative mutation identified in plakoglobin protein gene indicated a potential role of the desmosomal protein complex as culprit for cardiomyopathy. In the context of a family, the early evident cutaneous features may serve as a clinical screening tool to spot arrhythmogenic cardiomyopathy in subclinical stage. "Myocarditis-like episodes" may step up the disease evolution or mark a transition from concealed to symptomatic cardiomyopathy phase. Arrhythmogenic cardiomyopathy in Naxos disease shows increased penetrance and phenotypic expression but its arrhythmic risk is analogous to dominant forms.

Arrhythmogenic right ventricular cardiomyopathy in patients with biallelic JUP-associated skin fragility

Arrhythmogenic right ventricular cardiomyopathy (ARVC), with skin manifestations, has been associated with mutations in JUP encoding plakoglobin. Genotype–phenotype correlations regarding the penetrance of cardiac involvement, and age of onset have not been well established. We examined a cohort of 362 families with skin fragility to screen for genetic mutations with next-generation sequencing-based methods. In two unrelated families, a previously unreported biallelic mutation, JUP: c.201delC; p.Ser68Alafs^*92, was disclosed. The consequences of this mutation were determined by expression profiling both at tissue and ultrastructural levels, and the patients were evaluated by cardiac and cutaneous work-up. Whole-transcriptome sequencing by RNA-Seq revealed JUP as the most down-regulated gene among 21 skin fragility-associated genes. Immunofluorescence showed the lack of plakoglobin in the epidermis. Two probands, 2.5 and 22-year-old, with the same homozygous mutation, allowed us to study the cross-sectional progression of cardiac involvements in relation to age. The older patient had anterior T wave inversions, prolonged terminal activation duration (TAD), and RV enlargement by echocardiogram, and together with JUP mutation met definite ARVC diagnosis. The younger patient had no evidence of cardiac disease, but met possible ARVC diagnosis with one major criterion (the JUP mutation). In conclusion, we identified the same biallelic homozygous JUP mutation in two unrelated families with skin fragility, but cardiac findings highlighted age-dependent penetrance of ARVC. Thus, young, phenotypically normal patients with biallelic JUP mutations should be monitored for development of ARVC.

Mutations in genes encoding desmosomal proteins: spectrum of cutaneous and extracutaneous abnormalities

The desmosome is a type of intercellular junction found in epithelial cells, cardiomyocytes and other specialized cell types. Composed of a network of transmembranous cadherins and intracellular armadillo, plakin and other proteins, desmosomes contribute to cell-cell adhesion, signalling, development and differentiation. Mutations in genes encoding desmosomal proteins result in a spectrum of erosive skin and mucosal phenotypes that also may affect hair or heart. This review summarizes the molecular pathology and phenotypes associated with desmosomal dysfunction with a focus on inherited disorders that involve the skin/hair, as well as associated extracutaneous pathologies. We reviewed the relevant literature to collate studies of pathogenic human mutations in desmosomes that have been reported over the last 25 years. Mutations in 12 different desmosome genes have been documented, with mutations in nine genes affecting the skin/mucous membranes (DSG1, DSG3, DSC2, DSC3, JUP, PKP1, DSP, CDSN, PERP) and eight resulting in hair abnormalities (DSG4, DSC2, DSC3, JUP, PKP1, DSP, CDSN, PERP). Mutations in three genes can result in cardiocutaneous syndromes (DSC2, JUP, DSP), although mutations have been described in five genes in inherited heart disorders that may lack any dermatological manifestations (DSG2, DSC2, JUP, PKP2, DSP). Understanding the diverse nature of these clinical phenotypes, as well as the desmosome gene mutation(s), has clinical value in managing and counselling patients, as well as demonstrating the biological role and activity of specific components of desmosomes in skin and other tissues.

Whole-Exome Sequencing Identified a De Novo Mutation of Junction Plakoglobin (p.R577C) in a Chinese Patient with Arrhythmogenic Right Ventricular Cardiomyopathy

Arrhythmogenic right ventricular cardiomyopathy (ARVC) is a rare and potentially life-threatening disorder of the heart. The clinical spectrum of ARVC includes myocyte loss and fibro-fatty tissue replacement. With the progress of ARVC, the patient can present serious ventricular arrhythmias, heart failure, and even sudden cardiac death. Previous studies have demonstrated that desmosomes and intermediate junctions play a crucial role in the generation and development of ARVC. In this study, we enrolled a Chinese patient with suspicious ARVC. The patient suffered from right ventricular enlargement and less thickening of right ventricular wall. ECG record showed an epsilon wave. However, there was no obvious symptom in his parents. After whole-exome sequencing and data filtering, we identified a de novo mutation (c.1729C>T/p.R577C) of junction plakoglobin (JUP) in this patient. Bioinformatics programs predicted that this mutation was deleterious. Western blot revealed that, compared to cells transfected with WT plasmids, the expressions of desmoglein 2 (DSG2) and Connexin 43 were decreased overtly in cells transfected with the mutant plasmid. Previous studies have proven that the reduction of DSG2 and Connexin 43 may disturb the stability of desmosomes. In this research, we reported a novel de novo mutation (c.1729C>T/p.R577C) of JUP in a Chinese patient with suspicious ARVC. Functional research further confirmed the pathogenicity of this novel mutation. Our study expanded the spectrum of JUP mutations and may contribute to the genetic diagnosis and counseling of patients with ARVC.

Clinical subtypes and molecular basis of epidermolysis bullosa in Kuwait

BACKGROUND

Epidermolysis bullosa (EB) is a clinically and genetically heterogeneous blistering skin disease, but in countries such as Kuwait, there are very limited data on the clinical and molecular pathology of EB. To improve understanding of EB in Kuwait, we report the experience of a local tertiary referral center over a 17.5 year period (January 2000-June 2017) in establishing clinical and molecular diagnoses.

METHODS

Review of hospital records and diagnostic reports. Individual cases were diagnosed by combinations of clinical assessment, skin biopsy (immunohistochemistry and transmission electron microscopy), Sanger sequencing of EB genes, and whole exome sequencing.

RESULTS

Fifty-four families with EB were registered with the clinic over this period, 41 of whom (84 patients) participated in diagnostic studies. Thirty-seven of these 41 families had consanguineous marriages; 34 had recessive forms of EB, while only seven had dominant subtypes. Recurrent mutations were observed in epidermal dystonin, transglutaminase 5, and type VII collagen.

CONCLUSIONS

The prevalence of EB in Kuwait is approximately three times that of internationally cited rates with an over-representation of autosomal recessive variants. Establishing the molecular basis of EB in Kuwait with accurate diagnostic subtyping provides a basis for determining healthcare requirements and improving patient management of EB.

A Novel Mutation in Junctional Plakoglobin Causing Lethal Congenital Epidermolysis Bullosa

We report a case of neonatal generalized erythema and epidermolysis resulting from a novel mutation in the junctional plakoglobin gene causing truncation of the plakoglobin protein. Expedited genetic testing enabled diagnosis while the patient was in the neonatal intensive care unit, providing valuable information for the clinicians and family.

Arrhythmogenic Right Ventricular Dysplasia in Neuromuscular Disorders

OBJECTIVES

Arrhythmogenic right ventricular dysplasia (ARVD) is a rare, genetic disorder predominantly affecting the right ventricle. There is increasing evidence that in some cases, ARVD is due to mutations in genes, which have also been implicated in primary myopathies. This review gives an overview about myopathy-associated ARVD and how these patients can be managed.

METHODS

A literature review was done using appropriate search terms.

RESULTS

The myopathy, which is most frequently associated with ARVD, is the myofibrillar myopathy due to desmin mutations. Only in a single patient, ARVD was described in myotonic dystrophy type 1. However, there are a number of genes causing either myopathy or ARVD. These genes include lamin A/C, ZASP/cypher, transmembrane protein-43, titin, and the ryanodine receptor-2 gene. Diagnosis and treatment are identical for myopathy-associated ARVD and nonmyopathy-associated ARVD.

CONCLUSIONS

Patients with primary myopathy due to mutations in the desmin, dystrophia myotonica protein kinase, lamin A/C, ZASP/cypher, transmembrane protein-43, titin, or the ryanodine receptor-2 gene should be screened for ARVD. Patients carrying a pathogenic variant in any of these genes should undergo annual cardiological investigations for cardiac function and arrhythmias.