Laing distal myopathy pathologically resembling inclusion body myositis

Exploring challenges in the management and treatment of inclusion body myositis

PURPOSE OF REVIEW

This review provides an overview of the management and treatment landscape of inclusion body myositis (IBM), while highlighting the current challenges and future directions.

RECENT FINDINGS

IBM is a slowly progressive myopathy that predominantly affects patients over the age of 40, leading to increased morbidity and mortality. Unfortunately, a definitive cure for IBM remains elusive. Various clinical trials targeting inflammatory and some of the noninflammatory pathways have failed. The search for effective disease-modifying treatments faces numerous hurdles including variability in presentation, diagnostic challenges, poor understanding of pathogenesis, scarcity of disease models, a lack of validated outcome measures, and challenges related to clinical trial design. Close monitoring of swallowing and respiratory function, adapting an exercise routine, and addressing mobility issues are the mainstay of management at this time.

SUMMARY

Addressing the obstacles encountered by patients with IBM and the medical community presents a multitude of challenges. Effectively surmounting these hurdles requires embracing cutting-edge research strategies aimed at enhancing the management and treatment of IBM, while elevating the quality of life for those affected.

Pathogenic variants in three families with distal muscle involvement

Three families suspected of distal hereditary motor neuropathy underwent genetic screening with the aim to identify the molecular defect underlying the disease. The description of the identification reflects the shift in molecular diagnostics that was made during the last decades. Our candidate gene approach yielded a known pathogenic variant in BSCL2 (p.Asn88Ser) in one family, and via a CMT-capture, in HSPB1 (p.Arg127Trp), in addition to five other variations in Charcot-Marie-Tooth-related genes in the proband of the second family. In the third family, using whole exome sequencing, followed by linkage-by-location, a three base pair deletion in exon 33 of MYH7 (p.Glu1508del) was found, a reported pathogenic allele albeit for a myopathy. After identification of the causative molecular defect, cardiac examination was performed for patients of the third family and this demonstrated abnormalities in three out of five affected family members. Heterogeneity and expansion of clinical phenotypes beyond known characteristics requires a wider set of genes to be screened. Whole exome/genome analysis with limited prior clinical information may therefore be used to precede a detailed clinical evaluation in cases of large families, preventing screening of a too narrow set of genes, and enabling the identification of novel disease-associated genes. In our cases, the variants had been reported, and co-segregation analysis confirmed the molecular diagnosis.

Clinical features and genotypes of Laing distal myopathy in a group of Chinese patients, with in-frame deletions of MYH7 as common mutations

Background

Laing distal myopathy is a rare autosomal dominant inherited distal myopathy caused by mutations of the MYH7 gene affecting mainly the rod region. We described the clinical features, muscle MRI and pathological changes as well as genetic mutations in a group of Chinese patients with Laing distal myopathy.

Results

Six patients with the confirmed diagnoses of Laing distal myopathy were recruited. Ankle dorsiflexion and finger extension weakness, as well as neck flexion weakness were common in our patients. Myopathic as well as neurogenic lesions were suggested by electromyography in different patients. Respiratory abnormality of sleep apnea was detected in two of our patients stressing the necessity of close respiratory monitoring in this disease. Muscle MRIs showed similar features of concentric fatty infiltration of anterior thigh muscles together with early involvement of tibialis anterior and extensor hallucis longus. However, muscle pathological presentations were varied depending on the biopsied muscles and the severity of the disease. In-frame deletions of the MYH7 gene made up 3/4 of mutations in our patients, suggesting that these are common mutations of Laing distal myopathy.

Conclusions

Our study further expanded the phenotypes and genotypes of Laing distal myopathy. In-frame deletions of the MYH7 gene are common causes of Laing distal myopathy.

Myopathies with finger flexor weakness: Not only inclusion-body myositis

Muscle disorders are characterized by differential involvement of various muscle groups. Among these, weakness predominantly affecting finger flexors is an uncommon pattern, most frequently found in sporadic inclusion-body myositis. This finding is particularly significant when the full range of histopathological findings of inclusion-body myositis is not found on muscle biopsy. Prominent finger flexor weakness, however, is also observed in other myopathies. It occurs commonly in myotonic dystrophy types 1 and 2. In addition, individual reports and small case series have documented finger flexor weakness in sarcoid and amyloid myopathy, and in inherited myopathies caused by ACTA1, CRYAB, DMD, DYSF, FLNC, GAA, GNE, HNRNPDL, LAMA2, MYH7, and VCP mutations. Therefore, the finding of finger flexor weakness requires consideration of clinical, myopathological, genetic, electrodiagnostic, and sometimes muscle imaging findings to establish a diagnosis.

[A case of Japanese Laing type distal myopathy with a mutation in MYH7 gene]

A 67-year-old man developed weakness and atrophy of the anterior compartment of the lower leg at age 53 years, followed by weakness of proximal muscles of the upper limb. His father had difficulties in walking in his thirties and died of heart disease at age 45 years. He also had mild respiratory weakness without cardiac involvement. Muscle histology showed spheroid or cytoplasmic bodies-like inclusions with moth-eaten appearance and irregular intramyofibrillar network. Electron microscopy revealed abnormally thickened and disorganized Z lines (Z line streaming) between the surrounding myofibrils and electron-dense globular deposits. These pathological findings apparently suggested myofibrillar myopathy. However, genetic analysis revealed a mutation (c.5566G>A, p.E1856K) in MYH7 gene, that is responsible for Laing-type distal myopathy (LDM). This mutation was previously reported in a study from Austria. This is the first report of LDM in the Japanese population .

Sporadic inclusion body myositis - a myodegenerative disease or an inflammatory myopathy

Sporadic inclusion body myositis (sIBM) is an insidious late-onset progressive myopathy that typically affects patients over the age of 50. Clinically, patients develop a characteristic pattern of weakness that affects the forearm flexors and knee extensors. Muscle biopsy, often utilized in the diagnosis, demonstrates a chronic myopathy with mixed pathologies harbouring intramyofiber protein inclusions and endomysial inflammation. The co-existence of these pathologic features (that is, inflammation and protein aggregation) has divided the field of sIBM research into two opposing (albeit slowly unifying) camps regarding disease pathogenesis. The present review explores the recent evidence supporting these distinct pathogenic mechanisms. Future therapies that are designed to target both aspects of sIBM pathologies will likely be necessary to treat sIBM.

New Developments in the Genetics of Inclusion Body Myositis

PURPOSE OF REVIEW

Our goal is to review the recent literature pertaining to the genetics of sporadic inclusion body myositis (IBM).

RECENT FINDINGS

In a study of 252 IBM patients, the class II MHC allele HLA-DRB1*03:01 showed the most significant association with IBM, and that risk could be largely attributed to amino acids within the peptide-binding pocket. Candidate gene sequencing identified rare missense variants in proteins regulating protein homeostasis including VCP and SQSTM1. An unbiased approach employing exome sequencing of genes encoding rimmed vacuole proteins identified FYCO1 variants in IBM. Ongoing GWAS approaches may shed new light on genetic risk factors for IBM. Many variants have been reported at an increased frequency in IBM in small studies; however, only HLA association has shown genome-wide significance. Future studies are needed to validate variants in larger cohorts and to understand the molecular roles these risk factors play in IBM.

A missense mutation in MYH1 is associated with susceptibility to immune-mediated myositis in Quarter Horses

Background

The cause of immune-mediated myositis (IMM), characterized by recurrent, rapid-onset muscle atrophy in Quarter Horses (QH), is unknown. The histopathologic hallmark of IMM is lymphocytic infiltration of myofibers. The purpose of this study was to identify putative functional variants associated with equine IMM.

Methods

A genome-wide association (GWA) study was performed on 36 IMM QHs and 54 breed matched unaffected QHs from the same environment using the Equine SNP50 and SNP70 genotyping arrays.

Results

A mixed model analysis identified nine SNPs within a ~ 2.87 Mb region on chr11 that were significantly (P_unadjusted < 1.4 × 10^− 6) associated with the IMM phenotype. Associated haplotypes within this region encompassed 38 annotated genes, including four myosin genes (MYH1, MYH2, MYH3, and MYH13). Whole genome sequencing of four IMM and four unaffected QHs identified a single segregating nonsynonymous E321G mutation in MYH1 encoding myosin heavy chain 2X. Genotyping of additional 35 IMM and 22 unaffected QHs confirmed an association (P = 2.9 × 10^− 5), and the putative mutation was absent in 175 horses from 21 non-QH breeds. Lymphocytic infiltrates occurred in type 2X myofibers and the proportion of 2X fibers was decreased in the presence of inflammation. Protein modeling and contact/stability analysis identified 14 residues affected by the mutation which significantly decreased stability.

Conclusions

We conclude that a mutation in MYH1 is highly associated with susceptibility to the IMM phenotype in QH-related breeds. This is the first report of a mutation in MYH1 and the first link between a skeletal muscle myosin mutation and autoimmune disease.

Electronic supplementary material

The online version of this article (10.1186/s13395-018-0155-0) contains supplementary material, which is available to authorized users.

A Man With Distal Asymmetric Leg Weakness

EDUCATIONAL OBJECTIVES

To discuss a case of adult-onset asymmetric distal leg weakness in a patient who presented with weakness and atrophy of the posterior compartment of the left leg.

KEY QUESTIONS

1. What is the differential diagnosis of asymmetric distal leg weakness?2. How would a clinician approach diagnostic testing for such a patient?3. What is the final diagnosis for this patient?4. How to treat this patient?