A review of mitochondrial disease in dogs

Mitochondria are maternally inherited cellular organelles located in the cytoplasm of most eukaryotic cells. Mitochondrial diseases are a type of metabolic disorder, involving the respiratory chain under the control of both the mitochondrial DNA and nuclear DNA. In dogs, mitochondriopathies are considered rare, with few clinical syndromes having had their structural, biochemical and genetic basis identified. In this review, the basis for suspecting a mitochondrial disease clinically is summarised, with particular focus on mitochondrial encephalopathies, encephalomyelopathies and neuropathies. Recognisable confirmed mitochondriopathies including spongiform leukoencephalomyelopathy, Alaskan Husky encephalopathy, Leigh-like subacute necrotising encephalopathy and sensory ataxic neuropathy in the Golden Retriever are described in detail, alongside previously reported individual cases of presumptive mitochondriopathies of unknown origin. Genetic mutations reported in the literature are reviewed. A clear classification for mitochondrial diseases in veterinary medicine is lacking, and this review is the first to address this class of diseases specifically in dogs.

Progressive External Ophthalmoplegia in Polish Patients—From Clinical Evaluation to Genetic Confirmation

Mitochondrial encephalomyopathies comprise a group of heterogeneous disorders resulting from impaired oxidative phosphorylation (OxPhos). Among a variety of symptoms progressive external ophthalmoplegia (PEO) seems to be the most common. The aim of this study is to present clinical and genetic characteristics of Polish patients with PEO. Clinical, electrophysiological, neuroradiological, and morphological data of 84 patients were analyzed. Genetic studies of mitochondrial DNA (mtDNA) were performed in all patients. Among nuclear DNA (nDNA) genes POLG was sequenced in 41 patients, TWNK (C10orf2) in 13 patients, and RNASEH1 in 2 patients. Total of 27 patients were included in the chronic progressive external ophthalmoplegia (CPEO) group, 24 in the CPEO+ group. Twenty-six patients had mitochondrial encephalomyopathy (ME), six patients Kearns–Sayre syndrome (KSS), and one patient sensory ataxic neuropathy, dysarthria, ophthalmoparesis (SANDO) syndrome. Genetic analysis of nDNA genes revealed the presence of pathogenic or possibly pathogenic variants in the POLG gene in nine patients, the TWNK gene in five patients and the RNASEH1 gene in two patients. Detailed patients’ history and careful assessment of family history are essential in the diagnostic work-up. Genetic studies of both mtDNA and nDNA are necessary for the final diagnosis of progressive external ophthalmoplegia and for genetic counseling.

Guillain-Barré syndrome: The first documented COVID-19–triggered autoimmune neurologic disease

ObjectiveTo present the COVID-19–associated GBS, the prototypic viral-triggered autoimmune disease, in the context of other emerging COVID-19–triggered autoimmunities, and discuss potential concerns with ongoing neuroimmunotherapies.MethodsEleven GBS cases in four key COVID-19 hotspots are discussed regarding presenting symptoms, response to therapies and cross-reactivity of COVID spike proteins with nerve glycolipids. Emerging cases of COVID-19–triggered autoimmune necrotizing myositis (NAM) and encephalopathies are also reviewed in the context of viral invasion, autoimmunity and ongoing immunotherapies.ResultsCollective data indicate that in this pandemic any patient presenting with an acute paralytic disease-like GBS, encephalomyelitis or myositis-even without systemic symptoms, may represent the first manifestation of COVID-19. Anosmia, ageusia, other cranial neuropathies and lymphocytopenia are red flags enhancing early diagnostic suspicion. In Miller-Fisher Syndrome, ganglioside antibodies against GD1b, instead of QG1b, were found; because the COVID-19 spike protein also binds to sialic acid-containing glycoproteins for cell-entry and anti-GD1b antibodies typically cause ataxic neuropathy, cross-reactivity between COVID-19–bearing gangliosides and peripheral nerve glycolipids was addressed. Elevated Creatine Kinase (>10,000) is reported in 10% of COVID-19–infected patients; two such patients presented with painful muscle weakness responding to IVIg indicating that COVID-19–triggered NAM is an overlooked entity. Cases of acute necrotizing brainstem encephalitis, cranial neuropathies with leptomeningeal enhancement, and tumefactive postgadolinium-enhanced demyelinating lesions are now emerging with the need to explore neuroinvasion and autoimmunity. Concerns for modifications-if any-of chronic immunotherapies with steroids, mycophenolate, azathioprine, IVIg, and anti-B-cell agents were addressed; the role of complement in innate immunity to viral responses and anti-complement therapeutics (i.e. eculizumab) were reviewed.ConclusionsEmerging data indicate that COVID-19 can trigger not only GBS but other autoimmune neurological diseases necessitating vigilance for early diagnosis and therapy initiation. Although COVID-19 infection, like most other viruses, can potentially worsen patients with pre-existing autoimmunity, there is no evidence that patients with autoimmune neurological diseases stable on common immunotherapies are facing increased risks of infection.