A Clinical, Neuropathological and Genetic Study of Homozygous A467T POLG-Related Mitochondrial Disease

Mutations in the nuclear gene POLG (encoding the catalytic subunit of DNA polymerase gamma) are an important cause of mitochondrial disease. The most common POLG mutation, A467T, appears to exhibit considerable phenotypic heterogeneity. The mechanism by which this single genetic defect results in such clinical diversity remains unclear. In this study we evaluate the clinical, neuropathological and mitochondrial genetic features of four unrelated patients with homozygous A467T mutations. One patient presented with the severe and lethal Alpers-Huttenlocher syndrome, which was confirmed on neuropathology, and was found to have a depletion of mitochondrial DNA (mtDNA). Of the remaining three patients, one presented with mitochondrial encephalomyopathy, lactic acidosis and stroke-like episodes (MELAS), one with a phenotype in the Myoclonic Epilepsy, Myopathy and Sensory Ataxia (MEMSA) spectrum and one with Sensory Ataxic Neuropathy, Dysarthria and Ophthalmoplegia (SANDO). All three had secondary accumulation of multiple mtDNA deletions. Complete sequence analysis of muscle mtDNA using the MitoChip resequencing chip in all four cases demonstrated significant variation in mtDNA, including a pathogenic MT-ND5 mutation in one patient. These data highlight the variable and overlapping clinical and neuropathological phenotypes and downstream molecular defects caused by the A467T mutation, which may result from factors such as the mtDNA genetic background, nuclear genetic modifiers and environmental stressors

Designing clinical trials for rare diseases: unique challenges and opportunities

Orphan drug development is a rapidly expanding field. Nevertheless, clinical trials for rare diseases can present inherent challenges. Optimal study design and partnerships between academia and industry are therefore required for the successful development, delivery and clinical approval of effective therapies in this group of disorders

CAV3 mutations causing exercise intolerance, myalgia and rhabdomyolysis: expanding the phenotypic spectrum of caveolinopathies

Rhabdomyolysis is often due to a combination of environmental trigger(s) and genetic predisposition; however, the underlying genetic cause remains elusive in many cases. Mutations in CAV3 lead to various neuromuscular phenotypes with partial overlap, including limb girdle muscular dystrophy type 1C (LGMD1C), rippling muscle disease, distal myopathy and isolated hyperCKemia. Here we present a series of eight patients from seven families presenting with exercise intolerance and rhabdomyolysis caused by mutations in CAV3 diagnosed by next generation sequencing (NGS) (n=6). Symptoms included myalgia (n=7), exercise intolerance (n=6) and episodes of rhabdomyolysis (n=2). Percussion-induced rapid muscle contractions (PIRCs) were seen in five out of six patients examined. A previously reported heterozygous mutation in CAV3 (p.T78M) and three novel variants (p.V14I, p.F41S, p.F54V) were identified. Caveolin-3 immunolabeling in muscle was normal in 3/4 patients however, immunoblotting showed more than 50% reduction of caveolin-3 in five patients compared with controls. This case series demonstrates that exercise intolerance, myalgia and rhabdomyolysis may be caused by CAV3 mutations and broadens the phenotypic spectrum of caveolinopathies. In our series immunoblotting was a more sensitive method to detect reduced caveolin-3 levels than immunohistochemistry in skeletal muscle. Patients presenting with muscle pain, exercise intolerance and rhabdomyolysis should be routinely tested for PIRCs as this may be an important clinical clue for caveolinopathies, even in the absence of other “typical” features. The use of NGS may expand current knowledge concerning inherited diseases, and unexpected/atypical phenotypes may be attributed to well-known human disease genes

Mitochondrial Strokes: Diagnostic Challenges and Chameleons

Mitochondrial stroke-like episodes (SLEs) are a hallmark of mitochondrial encephalomyopathy, lactic acidosis, and stroke-like episodes (MELAS). They should be suspected in anyone with an acute/subacute onset of focal neurological symptoms at any age and are usually driven by seizures. Suggestive features of an underlying mitochondrial pathology include evolving MRI lesions, often originating within the posterior brain regions, the presence of multisystemic involvement, including diabetes, deafness, or cardiomyopathy, and a positive family history. The diagnosis of MELAS has important implications for those affected and their relatives, given it enables early initiation of appropriate treatment and genetic counselling. However, the diagnosis is frequently challenging, particularly during the acute phase of an event. We describe four cases of mitochondrial strokes to highlight the considerable overlap that exists with other neurological disorders, including viral and autoimmune encephalitis, ischemic stroke, and central nervous system (CNS) vasculitis, and discuss the clinical, laboratory, and imaging features that can help distinguish MELAS from these differential diagnoses

Development of Measure Yourself Concerns and Wellbeing for informal caregivers of people with cancer – a multicentred study

Purpose: Measure Yourself Concerns and Wellbeing (MYCaW) is a validated person-centred measure of the concerns and wellbeing of people affected by cancer. Research suggests that the concerns of informal caregivers (ICs) are as complex and severely rated as people with cancer, yet MYCaW has only been used to represent cancer patients’ concerns and wellbeing. This paper reports on the development of a new qualitative coding framework for MYCaW to capture the concerns of ICs, to better understand the needs of this group. Methods: This multicentred study involved collection of data from ICs receiving support from two UK cancer support charities (Penny Brohn UK and Cavendish Cancer Care). Qualitative codes were developed through a detailed thematic analysis of ICs’ stated concerns. Results: Thematic analysis of IC questionnaire data identified key themes which were translated into a coding framework with two overarching sections; 1. ‘informal caregiver concerns for self’ and 2. ‘informal caregiver concerns for the person with cancer’. Supercategories with specific accompanying codes were developed for each section. Two further rounds of framework testing across different cohorts allowed for iterative development and refinement of the framework content. Conclusions: This is the first person-centred tool specifically designed for capturing IC’s concerns through their own words. This coding framework will allow for IC data to be analysed using a rigorous and reproducible method, and therefore reported in a standardised way. This may also be of interest to those exploring the needs of ICs of people in other situations

Homozygous R627W mutations in POLG cause mitochondrial DNA depletion leading to encephalopathy, seizures and stroke-like episodes

Mutations in the mitochondrial DNA maintenance gene POLG (DNA Polymerase Gamma, Catalytic Subunit), encoding mitochondrial DNA polymerase gamma (pol γ), are associated with an extremely broad phenotypic spectrum. We identified homozygous POLG c.1879C>T; p.R627W mutations in two siblings from a consanguineous South Asian family following targeted resequencing of 75 nuclear-encoded mitochondrial genes. Both patients presented with encephalopathy, seizures and stroke-like episodes, and mitochondrial DNA depletion was confirmed in the proband's muscle tissue. Subsequent Sanger sequencing of POLG in a further 275 unrelated probands with genetically unconfirmed mitochondrial disease revealed a third unrelated proband with a similar phenotype harboring homozygous c.1879C>T; p.R627W mutations and a fourth patient, with a milder clinical disorder, harboring compound heterozygous POLG c.1879C>T; p.R627W and c.2341G>A; p.A781T mutations. Given endogamous practices in the Indian subcontinent, homozygous POLG c.1879C>T; p.R627W mutations should be excluded in South Asian patients presenting with encephalopathy, seizures and stroke-like episodes

Enhanced mitochondrial genome analysis: bioinformatic and long-read sequencing advances and their diagnostic implications

Introduction: Primary mitochondrial diseases (PMDs) comprise a large and heterogeneous group of genetic diseases that result from pathogenic variants in either nuclear DNA (nDNA) or mitochondrial DNA (mtDNA). Widespread adoption of next-generation sequencing (NGS) has improved the efficiency and accuracy of mtDNA diagnoses; however, several challenges remain. Areas covered: In this review, we briefly summarize the current state of the art in molecular diagnostics for mtDNA and consider the implications of improved whole genome sequencing (WGS), bioinformatic techniques, and the adoption of long-read sequencing, for PMD diagnostics. Expert opinion: We anticipate that the application of PCR-free WGS from blood DNA will increase in diagnostic laboratories, while for adults with myopathic presentations, WGS from muscle DNA may become more widespread. Improved bioinformatic strategies will enhance WGS data interrogation, with more accurate delineation of mtDNA and NUMTs (nuclear mitochondrial DNA segments) in WGS data, superior coverage uniformity, indirect measurement of mtDNA copy number, and more accurate interpretation of heteroplasmic large-scale rearrangements (LSRs). Separately, the adoption of diagnostic long-read sequencing could offer greater resolution of complex LSRs and the opportunity to phase heteroplasmic variants

Optimizing rare disorder trials: A phase 1a/1b randomized study of KL1333 in adults with mitochondrial disease

\ua9 2024 The Author(s). Over the past two decades there has been increased interest in orphan drug development for rare diseases. However, hurdles to clinical trial design for these disorders remain. This phase 1a/1b study addressed several challenges, while evaluating the safety and tolerability of the novel oral molecule KL1333 in healthy volunteers and subjects with primary mitochondrial disease. KL1333 aims to normalize the NAD+:NADH ratio that is critical for ATP production. The trial incorporated innovative design elements with potential translatability to other rare diseases including patient involvement, adaptive design and exploratory objectives, all of which have subsequently informed the protocol of an ongoing phase 2, pivotal efficacy study of KL1333. Results indicate KL1333 is safe and well tolerated, with dose-dependent gastrointestinal side effects, and validate potential novel outcome measures in primary mitochondrial disease including the 30-s Sit to Stand, and the patient-reported fatigue scales. Importantly, the data from the trial support efficacy of KL1333 based on improvements in fatigue and functional strength and endurance. Furthermore, the study highlights the value in using phase 1 studies to capture data that helps optimize later phase efficacy trial design

Constitutive activation of the PI3K-Akt-mTORC1 pathway sustains the m.3243 A > G mtDNA mutation

Mutations of the mitochondrial genome (mtDNA) cause a range of profoundly debilitating clinical conditions for which treatment options are very limited. Most mtDNA diseases show heteroplasmy – tissues express both wild-type and mutant mtDNA. While the level of heteroplasmy broadly correlates with disease severity, the relationships between specific mtDNA mutations, heteroplasmy, disease phenotype and severity are poorly understood. We have carried out extensive bioenergetic, metabolomic and RNAseq studies on heteroplasmic patient-derived cells carrying the most prevalent disease related mtDNA mutation, the m.3243 A > G. These studies reveal that the mutation promotes changes in metabolites which are associated with the upregulation of the PI3K-Akt-mTORC1 axis in patient-derived cells and tissues. Remarkably, pharmacological inhibition of PI3K, Akt, or mTORC1 reduced mtDNA mutant load and partially rescued cellular bioenergetic function. The PI3K-Akt-mTORC1 axis thus represents a potential therapeutic target that may benefit people suffering from the consequences of the m.3243 A > G mutation

Reducing Intrathecal Baclofen Related Infections: Service Evaluation and Best Practice Guidelines

Objectives: Intrathecal baclofen (ITB) pumps are an effective treatment for spasticity; however infection rates have been reported in 3–26% of patients in the literature. The multidisciplinary ITB service has been established at The National Hospital for Neurology and Neurosurgery, UCLH, Queen Square, London for over 20 years. Our study was designed to clarify the rate of infection in our ITB patient cohort and secondly, to formulate and implement best practice guidelines and to determine prospectively, whether they effectively reduced infection rates. / Methods: Clinical record review of all patients receiving ITB pre‐intervention; January 2013–May 2015, and following practice changes; June 2016–June 2018. / Results: Four of 118 patients receiving ITB during the first time period (3.4%, annual incidence rate of infection 1.4%) developed an ITB‐related infection (three following ITB pump replacement surgery, one after initial implant). Infections were associated with 4.2% of ITB‐related surgical procedures. Three of four pumps required explantation. Following change in practice (pre‐operative chlorhexidine skin wash and intraoperative vancomycin wash of the fibrous pocket of the replacement site), only one of 160 ITB patients developed infection (pump not explanted) in the second time period (0.6%, annual incidence rate 0.3%). The infection rate related to ITB surgical procedures was 1.1%. In cases of ITB pump replacement, the infection rate was reduced to 3.3% from 17.6%. / Conclusions: This study suggests that a straightforward change in clinical practice may lower infection rates in patients undergoing ITB therapy