Novel ancestral Dysferlin splicing mutation which migrated from the Iberian peninsula to South America

Dysferlinopathy misdiagnosed with juvenile polymyositis in the pre-symptomatic stage of hyperCKemia: a case report and literature review

Background

Dysferlinopathy encompasses a group of rare muscular dystrophies caused by recessive mutations in the DYSF gene. The phenotype ranges from asymptomatic elevated serum creatine kinase (hyperCKemia) to selective and progressive involvement of the proximal and/or distal muscles of the limbs. Bohan and Peter criteria are the most widely used for the diagnosis of polymyositis, but they have limitations and can misclassify muscular dystrophies with inflammation as polymyositis. Most dysferlinopathy patients have muscle biopsies with inflammation and thus are vulnerable to misdiagnosis with polymyositis and inappropriate treatment with steroids and immunosuppressors.

Case presentation

We describe a 14 years-old male patient who was referred for assessment of asymptomatic hyperCKemia (26,372 IU/L). An X-linked dystrophinopathy initially was ruled out by direct genetic testing. Juvenile polymyositis was considered based on muscle biopsy, creatine kinase levels, and electromyography changes. Corticosteroid treatment triggered proximal lower limb muscular weakness, and no full muscular strength recovery was observed after corticosteroid withdrawal. Based on these observations, a limb-girdle muscular dystrophy (LGMD) was suspected, and LGMDR2 was confirmed by whole exome sequencing.

Conclusion

We report a dysferlinopathy patient who was misdiagnosed with juvenile polymyositis and explore in a literature review how common such misdiagnoses are. With diagnosis based only on routine clinicopathological examinations, distinguishing an inflammatory myopathy from dysferlinopathy is quite difficult. We suggest that before establishing a diagnosis of “definite” or “probable” juvenile polymyositis, according to Bohan and Peter or current ACR/EULAR criteria, a muscular dystrophy must first be ruled out.

Genetic Appraisal of Hereditary Muscle Disorders In A Cohort From Mumbai, India

BACKGROUND

Hereditary muscle disorders are clinically and genetically heterogeneous. Limited information is available on their genetic makeup and their prevalence in India.

OBJECTIVE

To study the genetic basis of prevalent hereditary myopathies.

MATERIAL AND METHODS

This is a retrospective study conducted at a tertiary care center. The study was approved by the institutional ethics board. The point of the collection was the genetic database. The genetic data of myopathy patients for the period of two and half years (2019 to mid-2021) was evaluated. Those with genetic diagnoses of DMD, FSHD, myotonic dystrophies, mitochondriopathies, and acquired myopathies were excluded. The main outcome measures were diagnostic yield and the subtype prevalence with their gene variant spectrum.

RESULTS

The definitive diagnostic yield of the study was 39% (cases with two pathogenic variants in the disease-causing gene). The major contributing genes were GNE (15%), DYSF (13%), and CAPN3 (7%). Founder genes were documented in Calpainopathy and GNE myopathy. The uncommon myopathies identified were Laminopathy (0.9%), desminopathy (0.9%), and GMPPB-related myopathy (1.9%). Interestingly, a small number of patients showed pathogenic variants in more than one myopathy gene, the multigenic myopathies.

CONCLUSION

This cohort study gives hospital-based information on the prevalent genotypes of myopathies (GNE, Dysferlinopathy, and calpainopathy), founder mutations, and also newly documents the curious occurrence of multigenicity in a small number of myopathies.

A novel mutation in the DYSF gene in a patient with a presumed inflammatory myopathy

Dysferlinopathy, a progressive muscular dystrophy, results from mutations in the Dysferlin gene (DYSF, MIM*603009). Traditional diagnosis relies on the reduction or absence of dysferlin. However, altered dysferlin has been observed in other myopathies, leading to a precise diagnosis through molecular genetics. In this study, we report a patient who was previously misdiagnosed as inflammatory myopathy based on routine clinicopathological examinations alone. However, muscle biopsy specimens were analyzed further by immunohistochemistry of muscular dystrophy-related proteins, and gene-targeted next generation sequencing (NGS) was used to correctly identify muscular dystrophy. DNA was sequenced with NGS and the detected mutation was verified by Sanger sequencing. Our targeted NGS found a novel missense mutation (c.5392G > A) in the DYSF gene, allowing correct diagnosis of LGMD2B in our patient. We discovered of a novel missense mutation in the DYSF gene and have broadened the DYSF mutation spectrum, which may be correlated in patients with presumed dysferlinopathy, especially when lymphocytic infiltration is observed.

Limb-girdle Muscular Dystrophies in India: A Review

Limb-girdle muscular dystrophies (LGMDs) are common in India. Information on LGMDs has been gradually evolving in the recent years. This information is scattered in case series and case studies. The aim of this study is to collate available Indian information on LGMDs and put it in perspective. PubMed search using keywords such as limb-girdle muscular dystrophies in India, sarcoglycanopathies, dysferlinopathy, calpainopathy, and GNE myopathy was carried out. The published information on LGMDs in Indian context suggests that dysferlinopathy, calpainopathy, sarcoglycanopathies, and other myopathies such as GNE myopathy are frequently seen in India. Besides these, anecdotal reports of many other forms are available, some with genetic support and others showing immunocytochemical defects. The genotypic information on LGMDs is gradually evolving and founder mutations have been detected in selected populations. Further multicenter studies are necessary to document the incidence and prevalence of these common conditions in India.

Ancestral founder mutations in calpain-3 in the Indian Agarwal community: historical, clinical, and molecular perspective

INTRODUCTION

Clinical heterogeneity of limb-girdle muscular dystrophies (LGMDs, 24 known subtypes), which includes overlapping phenotypes and varying ages of onset and morbidity, adds complexity to clinical and molecular diagnoses.

METHODS

To diagnose LGMD subtype, protein analysis, using immunohistochemistry (IHC) and immunoblotting, was followed by gene sequencing through a panel approach (simultaneous sequencing of known LGMD genes) in 9 patients from unrelated families of the Indian Agarwal community. Haplotype studies were performed by targeted SNP genotyping to establish mutation segregation.

RESULTS

We identified 2 founder mutations in CAPN3, a missense (c.2338G>C; p.D780H) and a splice-site (c.2099-1G>T) mutation, on 2 different haplotype backgrounds. The patients were either heterozygous for both or homozygous for either of these mutations.

CONCLUSIONS

Founder mutations have immediate clinical application, at least in selected population groups. Clinically available gene panels may provide a definitive molecular diagnosis for heterogeneous disorders such as LGMD.