An “inflammatory” mitochondrial myopathy. A case report

Complex neurological and multisystem presentations in mitochondrial disease

Mitochondrial diseases typically involve organs highly dependent on aerobic metabolism and are often progressive with high morbidity and mortality. In the previous chapters of this book, classical mitochondrial phenotypes and syndromes are extensively described. However, these well-known clinical pictures are more the exception rather than the rule in mitochondrial medicine. In fact, more complex, unspecified, incomplete, and/or overlap clinical entities may be even more frequent, with multisystem appearance or progression. In this chapter, we describe some complex neurological presentations, as well as the multisystem manifestations of mitochondrial diseases, ranging from the brain to the other organs.

Anti-AQP4-IgG-positive Leigh syndrome: A case report and review of the literature

BACKGROUND

Leigh syndrome (LS; OMIM: 256000) is a progressive neurodegenerative disease caused by genetic mutations resulting in mitochondrial oxidative phosphorylation defects. The prognosis is poor, with most children dying before the age of 2 years. MT-ATP6 variants are the most common mitochondrial DNA mutations in LS. MT-ATP6 variant-induced LS may trigger autoimmunity, and immunotherapy might be effective. Here, we present the first pediatric case of anti-aquaporin 4 (AQP4)-IgG-positive LS caused by an MT-ATP6 variant.

CASE

A 1-year-old boy was hospitalized due to recurrent fever, cough, and developmental regression. Two months previously, he had developed reduced responses to stimulation and psychomotor retardation. After admission, his condition deteriorated and respiratory failure ensued. Magnetic resonance imaging of the brain showed symmetrical small patchy abnormal signals around the third ventricle, pons, and dorsal periaqueductal gray matter in the dorsal medulla. Laboratory tests revealed anti-AQP4-IgG antibodies. Anti-infection, immunoglobulin, and glucocorticoid therapy were administered for symptomatic treatment. Genetic testing revealed a de novo homogeneous pathogenic variant of MT-ATP6 (m.9176T > C, mutation ratio: 99.97%). The patient was diagnosed with anti-AQP4-IgG-positive LS, treated with "cocktail therapy" (vitamins B1, B2, C, and E, l-carnitine, and coenzyme Q10), and discharged after his condition improved. A literature review revealed that LS-induced mitochondrial defects can impact the immune system; hence, immunotherapy and early mitochondrial cocktail therapy may improve outcomes.

CONCLUSION

Anti-AQP4-IgG-positive LS is very rare. Patients with LS with the m.9176T  > C variant of MT-ATP6 may be susceptible to autoimmune damage of the central nervous system. Early cocktail therapy combined with immunotherapy may improve their prognosis.

The immune system as a driver of mitochondrial disease pathogenesis: a review of evidence

BACKGROUND

Genetic mitochondrial diseases represent a significant challenge to human health. These diseases are extraordinarily heterogeneous in clinical presentation and genetic origin, and often involve multi-system disease with severe progressive symptoms. Mitochondrial diseases represent the most common cause of inherited metabolic disorders and one of the most common causes of inherited neurologic diseases, yet no proven therapeutic strategies yet exist. The basic cell and molecular mechanisms underlying the pathogenesis of mitochondrial diseases have not been resolved, hampering efforts to develop therapeutic agents.

MAIN BODY

In recent pre-clinical work, we have shown that pharmacologic agents targeting the immune system can prevent disease in the Ndufs4(KO) model of Leigh syndrome, indicating that the immune system plays a causal role in the pathogenesis of at least this form of mitochondrial disease. Intriguingly, a number of case reports have indicated that immune-targeting therapeutics may be beneficial in the setting of genetic mitochondrial disease. Here, we summarize clinical and pre-clinical evidence suggesting a key role for the immune system in mediating the pathogenesis of at least some forms of genetic mitochondrial disease.

CONCLUSIONS

Significant clinical and pre-clinical evidence indicates a key role for the immune system as a significant in the pathogenesis of at least some forms of genetic mitochondrial disease.

Circulating cell-free mtDNA release is associated with the activation of cGAS-STING pathway and inflammation in mitochondrial diseases

BACKGROUND

There is increasing evidence for the role of inflammation in the pathogenesis of mitochondrial diseases (MDs). However, the mechanisms underlying mutation-induced inflammation in MD remain elusive. Our previous study suggested that mitophagy is impaired in the skeletal muscle of those with MD, likely causing mitochondrial DNA (mtDNA) release and thereby triggering inflammation. We here aimed to decipher the role of the cGAS-STING pathway in inflammatory process in MDs.

METHODS

We investigated the levels of circulating cell-free mtDNA (ccf-mtDNA) in the serum of 104 patients with MDs. Immunofluorescence was performed in skeletal muscles in MDs and control. Biochemical analysis of muscle biopsies was conducted with western blot to detect cGAS, STING, TBK1, IRF3 and phosphorylated IRF3 (p-IRF3). RT-qPCR was performed to detect the downstream genes of type I interferon in skeletal muscles. Furthermore, a protein microarray was used to examine the cytokine levels in the serum of patients with MDs.

RESULTS

We found that ccf-mtDNA levels were significantly increased in those with MDs compared to the controls. Consistently, the immunofluorescent results showed that cytosolic dsDNA levels were increased in the muscle samples of MD patients. Biochemical analysis of muscle biopsies showed that cGAS, IRF3, and TBK1 protein levels were significantly increased in those with MDs, indicating that there was activation of the cGAS-STING pathway. RT-qPCR showed that downstream genes of type I interferon were upregulated in muscle samples of MDs. Protein microarray results showed that a total of six cytokines associated with the cGAS-STING pathway were significantly increased in MD patients (fold change > 1.2, p value < 0.05).

CONCLUSIONS

These findings suggest that increases in ccf-mtDNA levels is associated with the activation of the cGAS-STING pathway, thereby triggering inflammation in MDs.

Clinicogenetical Variants of Progressive External Ophthalmoplegia - An Especial Review of Non-ophthalmic Manifestations

Progressive external ophthalmoplegia (PEO) is a slowly progressive myopathy characterized by extraocular muscles involvement, leading to frozen eyes without diplopia. The pattern of inheritance may be mitochondrial, autosomal dominant or, rarely, autosomal recessive. Sporadic forms were also reported. Muscular involvement other than extraocular muscles may occur with varying degrees of weakness, but this mostly happens many years after the disease begins. There are also scattered data about systemic signs besides ophthalmoplegia. This article aims to review non-ophthalmic findings of PEO from a clinicogenetical point of view.

Fulminant cerebral venous thrombosis associated with the m.3243A>G MELAS mutation: A new guise for an old disease

MELAS-syndrome (mitochondrial myopathy, encephalomyopathy, lactic acidosis, and stroke-like episodes) is a multisystem disorder with various presentations. Common clinical manifestations include stroke-like episodes, encephalopathy with seizures, muscle weakness, recurrent headaches and vomiting, hearing impairment, and short stature. Uncommon clinical presentations like cerebral venous thrombosis, which is almost unprecedented for MELAS-syndrome, impede correct diagnosis. We describe a novel presentation of MELAS-syndrome with severe cerebral venous thrombosis (CVT) and inflammation with a vasculopathy that affects the venous system as well. This case does not only extend the clinical spectrum of a multifaceted disease, but offers new clues for the pathomechanism of MELAS-syndrome.

A Mutation in the Mitochondrial Aspartate/Glutamate Carrier Leads to a More Oxidizing Intramitochondrial Environment and an Inflammatory Myopathy in Dutch Shepherd Dogs

BACKGROUND

Inflammatory myopathies are characterized by infiltration of inflammatory cells into muscle. Typically, immune-mediated disorders such as polymyositis, dermatomyositis and inclusion body myositis are diagnosed.

OBJECTIVE

A small family of dogs with early onset muscle weakness and inflammatory muscle biopsies were investigated for an underlying genetic cause.

METHODS

Following the histopathological diagnosis of inflammatory myopathy, mutational analysis including whole genome sequencing, functional transport studies of the mutated and wild-type proteins, and metabolomic analysis were performed.

RESULTS

Whole genome resequencing identified a pathological variant in the SLC25A12 gene, resulting in a leucine to proline substitution at amino acid 349 in the mitochondrial aspartate-glutamate transporter known as the neuron and muscle specific aspartate glutamate carrier 1 (AGC1). Functionally reconstituting recombinant wild-type and mutant AGC1 into liposomes demonstrated a dramatic decrease in AGC1 transport activity and inability to transfer reducing equivalents from the cytosol into mitochondria. Targeted, broad-spectrum metabolomic analysis from affected and control muscles demonstrated a proinflammatory milieu and strong support for oxidative stress.

CONCLUSIONS

This study provides the first description of a metabolic mechanism in which ablated mitochondrial glutamate transport markedly reduced the import of reducing equivalents into mitochondria and produced a highly oxidizing and proinflammatory muscle environment and an inflammatory myopathy.

Mitochondrial DNA Deletions With Low-Level Heteroplasmy in Adult-Onset Myopathy

We report the cases of 2 patients who presented to our Myositis Center with myalgias and elevated creatine kinase levels. Muscle biopsy showed pathological features consistent with mitochondrial myopathy. In both cases, a single large deletion in mitochondrial DNA at low-level heteroplasmy was identified by next-generation sequencing in muscle tissue. In 1 case, the deletion was identified in muscle tissue but not blood. In both cases, the deletion was only identified on next-generation sequencing of muscle mitochondrial DNA and missed on array comparative genome hybridization testing. These cases demonstrate that next-generation sequencing of mitochondrial DNA in muscle tissue is the most sensitive method of molecular diagnosis for mitochondrial myopathy due to mitochondrial DNA deletions.

Response to immunotherapy in a patient with adult onset Leigh syndrome and T9176C mtDNA mutation

Leigh syndrome is a mitochondrial disease caused by mutations in different genes, including ATP6A for which no known therapy is available. We report a case of adult-onset Leigh syndrome with response to immunotherapy. A twenty year-old woman with baseline learning difficulties was admitted with progressive behavioral changes, diplopia, headaches, bladder incontinence, and incoordination. Brain MRI and PET scan showed T2 hyperintensity and increased uptake in bilateral basal ganglia, respectively. Autoimmune encephalitis was suspected and she received plasmapheresis with clinical improvement. She was readmitted 4 weeks later with dysphagia and aspiration pneumonia. Plasmapheresis was repeated with resolution of her symptoms. Given the multisystem involvement and suggestive MRI changes, genetic testing was done, revealing a homoplasmic T9176C ATPase 6 gene mtDNA mutation. Monthly IVIG provided clinical improvement with worsening when infusions were delayed. Leigh syndrome secondary to mtDNA T9176C mutations could have an autoimmune mechanism that responds to immunotherapy.

Mutation in cytochrome b gene of mitochondrial DNA in a family with fibromyalgia is associated with NLRP3-inflammasome activation

BACKGROUND

Fibromyalgia (FM) is a worldwide diffuse musculoskeletal chronic pain condition that affects up to 5% of the general population. Many symptoms associated with mitochondrial diseases are reported in patients with FM such as exercise intolerance, fatigue, myopathy and mitochondrial dysfunction. In this study, we report a mutation in cytochrome b gene of mitochondrial DNA (mtDNA) in a family with FM with inflammasome complex activation.

METHODS

mtDNA from blood cells of five patients with FM were sequenced. We clinically and genetically characterised a patient with FM and family with a new mutation in mtCYB. Mitochondrial mutation phenotypes were determined in skin fibroblasts and transmitochondrial cybrids.

RESULTS

After mtDNA sequence in patients with FM, we found a mitochondrial homoplasmic mutation m.15804T>C in the mtCYB gene in a patient and family, which was maternally transmitted. Mutation was observed in several tissues and skin fibroblasts showed a very significant mitochondrial dysfunction and oxidative stress. Increased NLRP3-inflammasome complex activation was observed in blood cells from patient and family.

CONCLUSIONS

We propose further studies on mtDNA sequence analysis in patients with FM with evidences for maternal inheritance. The presence of similar symptoms in mitochondrial myopathies could unmask mitochondrial diseases among patients with FM. On the other hand, the inflammasome complex activation by mitochondrial dysfunction could be implicated in the pathophysiology of mitochondrial diseases.