Primary mitochondrial myopathy: 12-month follow-up results of an Italian cohort

Expanded-access use of elamipretide in a patient with membrane protein-associated neurodegeneration

This case report presents a progressively declining 17-year-old patient with membrane protein-associated neurodegeneration who demonstrated symptomatic improvements in her dysarthria, dysphagia, and gait, and objective improvements in her 6-minute walk test and 5 times sit-to-stand test during elamipretide treatment.

Walking test outcomes in adults with genetic neuromuscular diseases: a systematic literature review of their measurement properties

INTRODUCTION

Neuromuscular diseases (NMDs) include a large group of heterogeneous diseases. NMDs frequently involve gait disorders, which affect quality of life. Several walking tests and tools have been described in the literature, but there is no consensus regarding the use of walking tests and tools in NMDs or of their measurement properties for walking outcomes. The aim of this review is to present an overview of walking tests, including their measurement properties when used in adults with inherited or genetic NMDs. The aim is to help clinicians and researchers choose the most appropriate test for their objective.

EVIDENCE ACQUISITION

A systematic review was conducted after consulting MEDLINE (via PubMed), EMBASE, Science direct, Google Scholar and Cochrane Central Register of Controlled Trials databases for published studies in which walking outcome measurement properties were assessed. The validity, reliability, measurement error and responsiveness properties were evaluated in terms of statistical methods and methodological design qualities using the COnsensus-based Standards for the selection of health Measurement Instruments (COSMIN) guidelines.

EVIDENCE SYNTHESIS

We included 46 studies in NMDs. These studies included 15 different walking tests and a wide variety of walking outcomes, assessed with six types of walking tools. Overall, the 6MWT was the most studied test in terms of measurement properties. The methodological design and statistical methods of most studies evaluating construct validity, reliability and measurement error were "very good." The majority of outcome measurements were valid and reliable. However, studies on responsiveness as minimal important difference or minimal important change were lacking or were found to have inadequate methodological and statistical methods according to the COSMIN guidelines.

CONCLUSIONS

Most walking outcomes were found to be valid and reliable in NMDs. However, in view of the growing number of clinical trials, further studies are needed to clarify additional measurement properties.

Mitochondrial myopathies diagnosed in adulthood: clinico-genetic spectrum and long-term outcomes

Mitochondrial myopathies are frequently recognized in childhood as part of a broader multisystem disorder and often overlooked in adulthood. Herein, we describe the phenotypic and genotypic spectrum and long-term outcomes of mitochondrial myopathies diagnosed in adulthood, focusing on neuromuscular features, electrodiagnostic and myopathological findings and survival. We performed a retrospective chart review of adult patients diagnosed with mitochondrial myopathy at Mayo Clinic (2005-21). We identified 94 patients. Median time from symptom onset to diagnosis was 11 years (interquartile range 4-21 years). Median age at diagnosis was 48 years (32-63 years). Primary genetic defects were identified in mitochondrial DNA in 48 patients (10 with single large deletion, 38 with point mutations) and nuclear DNA in 29. Five patients had multiple mitochondrial DNA deletions or depletion without nuclear DNA variants. Twelve patients had histopathological features of mitochondrial myopathy without molecular diagnosis. The most common phenotypes included multisystem disorder (n = 30); mitochondrial encephalomyopathy, lactic acidosis and stroke-like episodes (14); limb myopathy (13); chronic progressive external ophthalmoplegia (12); and chronic progressive external ophthalmoplegia-plus (12). Isolated skeletal muscle manifestations occurred in 27%. Sixty-nine per cent had CNS and 21% had cardiac involvement. Mutations most frequently involved MT-TL1 (27) and POLG (17); however, a wide spectrum of established and novel molecular defects, with overlapping phenotypes, was identified. Electrodiagnostic studies identified myopathy (77%), fibrillation potentials (27%) and axonal peripheral neuropathy (42%, most common with nuclear DNA variants). Among 42 muscle biopsies available, median percentage counts were highest for cytochrome C oxidase negative fibres (5.1%) then ragged blue (1.4%) and ragged red fibres (0.5%). Skeletal muscle weakness was mild and slowly progressive (decline in strength summated score of 0.01/year). Median time to gait assistance was 5.5 years from diagnosis and 17 years from symptom onset. Thirty patients died, with median survival of 33.4 years from symptom onset and 10.9 years from diagnosis. Median age at death was 55 years. Cardiac involvement was associated with increased mortality [hazard ratio 2.36 (1.05, 5.29)]. There was no difference in survival based on genotype or phenotype. Despite the wide phenotypic and genotypic spectrum, mitochondrial myopathies in adults share similar features with slowly progressive limb weakness, contrasting with common multiorgan involvement and high mortality.

Mitochondrial myopathy without extraocular muscle involvement: a unique clinicopathologic profile

OBJECTIVE

Mitochondrial myopathy without extraocular muscles involvement (MiMy) represents a distinct form of mitochondrial disorder predominantly affecting proximal/distal or axial muscles, with its phenotypic, genotypic features, and long-term prognosis poorly understood.

METHODS

A cross-sectional study conducted at a national diagnostic center for mitochondrial disease involved 47 MiMy patients, from a cohort of 643 mitochondrial disease cases followed up at Qilu Hospital from January 1, 2000, to January 1, 2021. We compared the clinical, pathological, and genetic features of MiMy to progressive external ophthalmoplegia (PEO) and mitochondrial encephalomyopathy, lactic acidosis, and stroke-like episodes (MELAS) patients.

RESULTS

MiMy patients demonstrated a more pronounced muscle involvement syndrome, with lower 6MWT scores, higher FSS, and lower BMI compared to PEO and MELAS patients. Serum levels of creatinine kinase (CK), lactate, and growth and differentiation factor 15 (GDF15) were substantially elevated in MiMy patients. Nearly a third (31.9%) displayed signs of subclinical peripheral neuropathy, mostly axonal neuropathy. Muscle biopsies revealed that cytochrome c oxidase strong (COX-s) ragged-red fibers (RRFs) were a typical pathological feature in MiMy patients. Genetic analysis predominantly revealed mtDNA point pathogenic variants (59.6%) and less frequently single (12.8%) or multiple (4.2%) mtDNA deletions. During the follow-up, a majority (76.1%) of MiMy patients experienced stabilization or improvement after therapeutic intervention.

CONCLUSIONS

This study provides a comprehensive profile of MiMy through a large patient cohort, elucidating its unique clinical, genetic, and pathological features. These findings offer significant insights into the diagnostic and therapeutic management of MiMy, ultimately aiming to ameliorate patient outcomes and enhance the quality of life.

Characterization of Fatigue in Primary Mitochondrial Myopathies: Findings From a Qualitative Interview Study

Background and Objectives

Primary mitochondrial myopathies are genetic disorders that primarily affect peripheral skeletal muscles. Patients with primary mitochondrial myopathies often experience muscle weakness, fatigue, and other significant impacts on health-related quality of life. The aim of this noninterventional qualitative study was to collect the most bothersome fatigue-related symptoms and impacts reported by patients with primary mitochondrial myopathies and determine whether the questions included in an existing patient-reported outcome measure, the Modified Fatigue Impact Scale, are relevant and interpretable for this population.

Methods

The interviews contained a concept elicitation exercise to understand the most bothersome primary mitochondrial myopathies symptoms and impacts and a cognitive debriefing section to review the questions included in the Modified Fatigue Impact Scale for relevance and interpretability. Transcripts were coded using ATLAS.ti software.

Results

Interviews were conducted with 16 patients who were aged 16 years and older with a genetically confirmed and clinical diagnosis of symptomatic primary mitochondrial myopathies. Concept elicitation interviews established that while patients with mitochondrial myopathies reported a wide variety of symptoms and impacts, one of the most impactful symptoms discussed was fatigue. Cognitive debriefing interview results confirmed that the Modified Fatigue Impact Scale items were relevant, were interpretable, and largely captured patients' experience with fatigue.

Discussion

Fatigue was one of the most widely discussed experiences discussed by participants and was considered the most important symptom/impact to treat by most of the participants. The Modified Fatigue Impact Scale could be used in future clinical trials to measure treatment benefit in fatigue-related impacts.

Pathophysiology and Management of Fatigue in Neuromuscular Diseases

Fatigue is a major determinant of quality of life and motor function in patients affected by several neuromuscular diseases, each of them characterized by a peculiar physiopathology and the involvement of numerous interplaying factors. This narrative review aims to provide an overview on the pathophysiology of fatigue at a biochemical and molecular level with regard to muscular dystrophies, metabolic myopathies, and primary mitochondrial disorders with a focus on mitochondrial myopathies and spinal muscular atrophy, which, although fulfilling the definition of rare diseases, as a group represent a representative ensemble of neuromuscular disorders that the neurologist may encounter in clinical practice. The current use of clinical and instrumental tools for fatigue assessment, and their significance, is discussed. A summary of therapeutic approaches to address fatigue, encompassing pharmacological treatment and physical exercise, is also overviewed.

Navigating Life With Primary Mitochondrial Myopathies: The Importance of the Patient Voice and Implications for Clinical Practice

Primary mitochondrial myopathies (PMM) are rare disorders with diverse and progressive symptom presentations that cause a substantial, detrimental impact on the quality of life of patients and their caregivers. The burden of symptoms is compounded by their visibility and their unpredictable, progressive nature, leading to a sense of social stigmatization, limited autonomy, social isolation, and grief. There is also a lack of awareness and expertise in the medical community, which presents huge obstacles to diagnosis and provision of coordinated multidisciplinary care for these patients, along with a lack of disease-modifying treatments. The present commentary serves to raise awareness of the challenges faced by patients with PMM and their caregivers in their own words, including diagnostic delays, the burden of disease, and the need for further trials to develop disease-modifying treatments and improved understanding of the disease course. We also provide commentary on considerations for clinical practice, including the need for holistic care and multidisciplinary care teams, details of common 'red flag' symptoms, proposed diagnostic approaches, and suggested descriptions of multisystemic symptoms for physician-patient dialogue. In addition, we highlight the role patient advocacy and support groups play in supporting patients and providing access to reliable, up-to-date information and educational resources on these rare diseases.