Inflammatory and interferon gene expression signatures in patients with mitochondrial disease.

BACKGROUND: People with mitochondrial disease (MtD) are susceptible to metabolic decompensation and neurological symptom progression in response to an infection. Increasing evidence suggests that mitochondrial dysfunction may cause chronic inflammation, which may promote hyper-responsiveness to pathogens and neurodegeneration. We sought to examine transcriptional changes between MtD patients and healthy controls to identify common gene signatures of immune dysregulation in MtD. METHODS: We collected whole blood from a cohort of MtD patients and healthy controls and performed RNAseq to examine transcriptomic differences. We performed GSEA analyses to compare our findings against existing studies to identify commonly dysregulated pathways. RESULTS: Gene sets involved in inflammatory signaling, including type I interferons, interleukin-1ß and antiviral responses, are enriched in MtD patients compared to controls. Monocyte and dendritic cell gene clusters are also enriched in MtD patients, while T cell and B cell gene sets are negatively enriched. The enrichment of antiviral response corresponds with an independent set of MELAS patients, and two mouse models of mtDNA dysfunction. CONCLUSIONS: Through the convergence of our results, we demonstrate translational evidence of systemic peripheral inflammation arising from MtD, predominantly through antiviral response gene sets. This provides key evidence linking mitochondrial dysfunction to inflammation, which may contribute to the pathogenesis of primary MtD and other chronic inflammatory disorders associated with mitochondrial dysfunction.

Epitope-level profiling in children with mitochondrial disease reveals limitations in the antibacterial antibody repertoire.

INTRODUCTION: Immunometabolic studies in mice have suggested the importance of oxidative phosphorylation (OXPHOS) in humoral immunity. However, there are important distinctions between murine and human immunity. Furthermore, translational studies on the role of OXPHOS in humoral immunity are nearly absent from the biomedical literature. Children with primary OXPHOS deficiency (i.e., mitochondrial disease, MtD), are an important patient population for demonstrating the functional effects of this bioenergetic defect on humoral immunity. METHODS: To define whether OXPHOS deficiency extended to human B cells, we performed extracellular flux analysis on lymphoblastoid B cell lines from children with MtD and controls (N = 4/group). To expand the immune phenotype of B cell OXPHOS deficiency, we conducted a cross-sectional multiplex serology study of the antibacterial antibody repertoire in children with MtD (N = 16) and controls (N = 16) using phage display and immunoprecipitation sequencing (PhIPseq). The PhIPseq library contained >3000 peptides (i.e., epitopes) covering >40 genera and > 150 species of bacteria that infect humans. RESULTS: B cell lymphoblastoid cell lines from children with MtD displayed depressed baseline oxygen consumption, ATP production and reserve capacity, indicating that OXPHOS deficiency extended to these key cells in humoral immunity. Characterization of the bacterial exposome revealed comparable bacterial species between the two groups, mostly Streptococcus and Staphylococcus. The most common species of bacteria was S. pneumoniae. By interrogating the antibacterial antibody repertoire, we found that children with MtD had less robust antibody fold changes to common epitopes. Furthermore, we also found that children with MtD failed to show a direct relationship between the number of bacterial epitopes recognized and age, unlike controls. OXPHOS deficiency extends to B cells in children with MtD, leading to limitations in the antibacterial antibody repertoire. Furthermore, the timing of bacterial exposures was asynchronous, suggesting different periods of increased exposure or susceptibility. CONCLUSIONS: Overall, the antibacterial humoral response is distinctive in children with MtD, suggesting an important role for OXPHOS in B cell function.

Primary oxidative phosphorylation defects lead to perturbations in the human B cell repertoire.

Introduction: The majority of studies on oxidative phosphorylation in immune cells have been performed in mouse models, necessitating human translation. To understand the impact of oxidative phosphorylation (OXPHOS) deficiency on human immunity, we studied children with primary mitochondrial disease (MtD). Methods: scRNAseq analysis of peripheral blood mononuclear cells was performed on matched children with MtD (N = 4) and controls (N = 4). To define B cell function we performed phage display immunoprecipitation sequencing on a cohort of children with MtD (N = 19) and controls (N = 16). Results: Via scRNAseq, we found marked reductions in select populations involved in the humoral immune response, especially antigen presenting cells, B cell and plasma populations, with sparing of T cell populations. MTRNR2L8, a marker of bioenergetic stress, was significantly elevated in populations that were most depleted. mir4485, a miRNA contained in the intron of MTRNR2L8, was co-expressed. Knockdown studies of mir4485 demonstrated its role in promoting survival by modulating apoptosis. To determine the functional consequences of our findings on humoral immunity, we studied the antiviral antibody repertoire in children with MtD and controls using phage display and immunoprecipitation sequencing. Despite similar viral exposomes, MtD displayed antiviral antibodies with less robust fold changes and limited polyclonality. Discussion: Overall, we show that children with MtD display perturbations in the B cell repertoire which may impact humoral immunity and the ability to clear viral infections.

Inflammatory and interferon gene expression signatures in patients with mitochondrial disease.

Background: People with mitochondrial disease (MtD) are susceptible to metabolic decompensation and neurological symptom progression in response to an infection. Increasing evidence suggests that mitochondrial dysfunction may cause chronic inflammation, which may promote hyperresponsiveness to pathogens and neurodegeneration. Methods: We collected whole blood from a cohort of MtD patients and healthy controls and performed RNAseq to examine transcriptomic differences. We performed GSEA analyses to compare our findings against existing studies to identify commonly dysregulated pathways. Results: Gene sets involved in inflammatory signaling, including type I interferons, interleukin-1ß and antiviral responses, are enriched in MtD patients compared to controls. Monocyte and dendritic cell gene clusters are also enriched in MtD patients, while T cell and B cell gene sets are negatively enriched. The enrichment of antiviral response corresponds with an independent set of MELAS patients, and two mouse models of mtDNA dysfunction. Conclusions: Through the convergence of our results, we demonstrate translational evidence of systemic peripheral inflammation arising from MtD, predominantly through antiviral response gene sets. This provides key evidence linking mitochondrial dysfunction to inflammation, which may contribute to the pathogenesis of primary MtD and other chronic inflammatory disorders associated with mitochondrial dysfunction.

Risk mitigation behaviors to prevent infection in the mitochondrial disease community during the COVID-19 pandemic.

BACKGROUND: A challenge during the COVID-19 pandemic has been widespread adherence to risk-reducing behaviors. Individuals with mitochondrial disease (MtD) are special population with an increased risk of morbidity associated with infection. PURPOSE: To measure risk mitigation behaviors (RMBs) in families affected by MtD and identify factors that may influence these behaviors. METHODS: An online questionnaire was distributed in April and June 2020. Individuals with MtD or their caregivers completed the survey. RESULTS: We received 529 eligible responses with n = 312 completing all questions for our multivariate regression model. The most common RMBs were increased hand washing (96%), social distancing (94%), and avoiding public gatherings (93%). Higher numbers of recent healthcare visits (b = 0.62, p < 0.05) and expressed fear of the MtD patient contracting COVID-19 (b = 0.92, p < 0.05) were associated with more RMBs. Living in a rural community (b = -0.99,p < 0.05) and a history of COVID-19 testing (b = -2.14,p < 0.01) were associated with fewer RMBs. CONCLUSIONS: Our results suggest that during the COVID-19 pandemic, families affected by MtD have near universal adherence to basic RMBs. This may be motivated by fear of the severe morbidity associated with infection in MtD. Patients with frequent healthcare visits may be sicker and therefore take more precautions. Living in a rural community may also impact these behaviors. People who practice fewer RMBs may be more likely to seek testing. Our findings may generalize to other chronic diseases.

Undiagnosed COVID-19 in households with a child with mitochondrial disease.

Background: The impact of the COVID-19 pandemic on medically fragile populations, who are at higher risk of severe illness and sequelae, has not been well characterized. Viral infection is a major cause of morbidity in children with mitochondrial disease (MtD), and the COVID-19 pandemic represents an opportunity to study this vulnerable population. Methods: A convenience sampling cross-sectional serology study was conducted (October 2020 to June 2021) in households (N = 20) containing a child with MtD (N = 22). Samples (N = 83) were collected in the home using a microsampling apparatus and shipped to investigators. Antibodies against SARS-CoV-2 nucleocapsid (IgG), spike protein (IgG, IgM, IgA), and receptor binding domain (IgG, IgM, IgA) were determined by enzyme linked immunosorbent assay. Results: While only 4.8% of participants were clinically diagnosed for SARS-CoV-2 infection, 75.9% of study participants were seropositive for SARS-CoV-2 antibodies. Most samples were IgM positive for spike or RBD (70%), indicating that infection was recent. This translated to all 20 families showing evidence of infection in at least one household member. For the children with MtD, 91% had antibodies against SARS-CoV-2 and had not experienced any adverse outcomes at the time of assessment. For children with recent infections (IgM+ only), serologic data suggest household members as a source. Conclusions: COVID-19 was highly prevalent and undiagnosed in households with a child with MtD through the 2020-2021 winter wave of the pandemic. In this first major wave, children with MtD tolerated SARS-CoV-2 infection well, potentially due to household adherence to CDC recommendations for risk mitigation.

Short report: Vaccine attitudes in the age of COVID-19 for a population of children with mitochondrial disease.

BACKGROUND: Children with developmental disabilities are vulnerable to morbidity associated with COVID-19. AIMS: To understand attitudes toward routine childhood vaccinations versus the COVID-19 vaccine in a population of families affected by mitochondrial disease (MtD), a form of developmental disability. METHODS AND PROCEDURES: An online survey was administered via several advocacy groups for children with MtD. OUTCOMES AND RESULT: Eighty-six percent of families reported being up to date with the childhood vaccine schedule and seventy percent reported that their affected child receives the annual flu shot. However, only fifty percent reported that the benefits of the COVID-19 vaccine outweighed the risk for their affected child. One quarter of families expressed concern that their child may become sick or deteriorate after the COVID-19 vaccine. In comparison to other routine childhood vaccines, families expressed less confidence in the COVID-19 vaccine. CONCLUSIONS AND IMPLICATIONS: Families affected by this population of developmental disabilities are more comfortable with the vaccines included in the routine childhood immunization schedule than with the newly introduced COVID-19 vaccine, even despite this group's vulnerability.

Comprehensive profiling of the human viral exposome in households containing an at-risk child with mitochondrial disease during the 2020-2021 COVID-19 pandemic.

BACKGROUND: Viral infection is a major cause of morbidity in children with mitochondrial disease (MtD). As a result, families with children with MtD are highly adherent to risk mitigation behaviours (RMBs) advised by the Centers for Disease Control and Prevention during the COVID-19 pandemic that can modulate infection risk. METHODS: Deep serologic phenotyping of viral infections was performed via home-based sampling by combining SARS-CoV-2 serologic testing and phage display immunoprecipitation and sequencing. Samples were collected approximately 1 year apart (October 2020 to April 2021 and October 2021 to March 2022) on households containing a child with MtD. RESULTS: In contrast to our first collection in 2020-2021, SARS-CoV-2 antibody profiles for all participants in 2021-2022 were marked by greater isotype diversity and the appearance of neutralizing antibodies. Besides SARS-CoV-2, households (N = 15) were exposed to >38 different respiratory and gastrointestinal viruses during the study, averaging five viral infections per child with MtD. Regarding clinical outcomes, children with MtD (N = 17) experienced 34 episodes of illness resulting in 6 hospitalizations, with some children experiencing multiple episodes. Neurologic events following illness were recorded in five patients. Infections were identified via clinical testing in only seven cases. Viral exposome profiles were consistent with clinical testing and even identified infections not captured by clinical testing. CONCLUSIONS: Despite reported adherence to RMBs during the COVID-19 pandemic by families with a child with MtD, viral infection was pervasive. Not all infections resulted in illness in the child with MtD, suggesting that some were subclinical or asymptomatic. However, selected children with MtD did experience neurologic events. Our studies emphasize that viral infections are inexorable, emphasizing the need for further understanding of host-pathogen interactions through broad serologic surveillance.

Progressive cerebellar atrophy in a patient with complex II and III deficiency and a novel deleterious variant in SDHA: A Counseling Conundrum.

BACKGROUND: Complex II is an essential component of the electron transport chain, linking it with the tricarboxylic acid cycle. Its four subunits are encoded in the nuclear genome, and deleterious variants in these genes, including SDHA (OMIM 600857), are associated with a wide range of symptoms including neurological disease, cardiomyopathy, and neoplasia (paraganglioma-pheochromocytomas (PGL/PCC), and gastrointestinal stromal tumors). Deleterious variants of SDHA are most frequently associated with Leigh and Leigh-like syndromes. METHODS AND RESULTS: Here, we describe a case of a 9-year-old boy with tremor, nystagmus, hypotonia, developmental delay, significant ataxia, and progressive cerebellar atrophy. He was found to have biallelic variants in SDHA, a known pathogenic variant (c.91C>T (p.R31*)), and a variant of unknown significance (c.454G>A (p.E152K)). Deficient activity of complexes II and III was detected in fibroblasts from the patient consistent with a diagnosis of a respiratory chain disorder. CONCLUSION: We, therefore, consider whether c.454G>A (p.E152K) is, indeed, a pathogenic variant, and what implications it has for family members who carry the same variant.