Primary coenzyme Q10 deficiency-7: expanded phenotypic spectrum and a founder mutation in southern Chinese

Understanding coenzyme Q

Coenzyme Q (CoQ), also known as ubiquinone, comprises a benzoquinone head group and a long isoprenoid side chain. It is thus extremely hydrophobic and resides in membranes. It is best known for its complex function as an electron transporter in the mitochondrial electron transport chain (ETC) but is also required for several other crucial cellular processes. In fact, CoQ appears to be central to the entire redox balance of the cell. Remarkably, its structure and therefore its properties have not changed from bacteria to vertebrates. In metazoans, it is synthesized in all cells and is found in most, and maybe all, biological membranes. CoQ is also known as a nutritional supplement, mostly because of its involvement with antioxidant defenses. However, whether there is any health benefit from oral consumption of CoQ is not well established. Here we review the function of CoQ as a redox-active molecule in the ETC and other enzymatic systems, its role as a prooxidant in reactive oxygen species generation, and its separate involvement in antioxidant mechanisms. We also review CoQ biosynthesis, which is particularly complex because of its extreme hydrophobicity, as well as the biological consequences of primary and secondary CoQ deficiency, including in human patients. Primary CoQ deficiency is a rare inborn condition due to mutation in CoQ biosynthetic genes. Secondary CoQ deficiency is much more common, as it accompanies a variety of pathological conditions, including mitochondrial disorders as well as aging. In this context, we discuss the importance, but also the great difficulty, of alleviating CoQ deficiency by CoQ supplementation.

The Spectrum of clinical manifestations in newborns with the COQ4 mutation: case series and literature review

Background

Coenzyme Q10 (CoQ10) plays an important role in the electron transport chain within the human mitochondrial respiratory chain. The manifestations of this deficiency exhibit a diverse range. This study investigates the clinical manifestations of primary coenzyme Q10 deficiency in neonates with the COQ4 mutation to improve the diagnosis of the disease and the prognosis through targeted treatment.

Methods

We report 4 patients with primary coenzyme Q10 deficiency by COQ4 variants in neonates. A comprehensive literature search and review for original articles and case reports with COQ4 mutation published from January 1989 to November 2023 was performed through Pubmed. We review clinical manifestations, diagnostic approaches, and treatment monitoring in these and 20 previously reported patients.

Results

Within the cohort of four cases examined, three females and one male were identified from two distinct families. Specifically, case 1 and 2 consisted of monoamniotic twins. Cases 3 and 4 were siblings. A comprehensive review of 20 cases involving neonatal-onset COQ4 mutation was conducted. Half of the cases are Chinese. There was no statistically significant difference in the mortality between Chinese (9/12, 75%) and other regions (11/12, 91.7%) (P = 0.27). The survival time for the 24 cases was 60.0 ± 98.0 days (95% confidence interval CI: 0-252.0 days). The incidence of prenatal abnormalities in preterm infants was significantly higher than that in full-term infants (66.7% vs. 16.7%, P = 0.02). Hyperlactatemia was one of the most common manifestations, accounting for 75% of cases (18/24). Twenty of the 24 cases were diagnosed by whole exome sequencing. Only 9 patients received exogenous coenzyme Q10 treatment, and all the 4 surviving patients received coenzyme Q10 supplementation.

Conclusion

The prognosis of COQ4 mutation in the neonatal period indicates a low survival rate and an poor prognosis. This may be due to the incomplete understanding of the mechanism of how COQ4 gene defects lead to coenzyme Q10 deficiency and why CoQ10 supplementation does not respond well to treatment. To improve the diagnostic rate, in addition to genetic testing, mitochondrial functional verification should be prioritized in southern China, where the incidence is relatively high. It will facilitate more in-depth mechanistic studies.

Efficacy and Safety of Coenzyme Q10 Supplementation in Neonates, Infants and Children: An Overview

To date, there have been no review articles specifically relating to the general efficacy and safety of coenzyme Q10 (CoQ10) supplementation in younger subjects. In this article, we therefore reviewed the efficacy and safety of CoQ10 supplementation in neonates (less than 1 month of age), infants (up to 1 year of age) and children (up to 12 years of age). As there is no rationale for the supplementation of CoQ10 in normal younger subjects (as there is in otherwise healthy older subjects), all of the articles in the medical literature reviewed in the present article therefore refer to the supplementation of CoQ10 in younger subjects with a variety of clinical disorders; these include primary CoQ10 deficiency, acyl CoA dehydrogenase deficiency, Duchenne muscular dystrophy, migraine, Down syndrome, ADHD, idiopathic cardiomyopathy and Friedreich's ataxia.

Biallelic variants in the COQ4 gene caused hereditary spastic paraplegia predominant phenotype

INTRODUCTION

Hereditary spastic paraplegias (HSPs) comprise a group of neurodegenerative disorders characterized by progressive degeneration of upper motor neurons. Homozygous or compound heterozygous variants in COQ4 have been reported to cause primary CoQ10 deficiency-7 (COQ10D7), which is a mitochondrial disease.

AIMS

We aimed to screened COQ4 variants in a cohort of HSP patients.

METHODS

A total of 87 genetically unidentified HSP index patients and their available family members were recruited. Whole exome sequencing (WES) was performed in all probands. Functional studies were performed to identify the pathogenicity of those uncertain significance variants.

RESULTS

In this study, five different COQ4 variants were identified in three Chinese HSP pedigrees and two variants were novel, c.87dupT (p.Arg30*), c.304C>T (p.Arg102Cys). More importantly, we firstly described two early-onset pure HSP caused by COQ4 variants. Functional studies in patient-derived fibroblast lines revealed a reduction cellular CoQ10 levels and the abnormal mitochondrial structure.

CONCLUSIONS

Our findings revealed that bilateral variants in the COQ4 gene caused HSP predominant phenotype, expanding the phenotypic spectrum of the COQ4-related disorders.

Two Turkish patients with Primary Coenzyme Q10 Deficiency-7: case report and literature review

OBJECTIVES

Primary Coenzyme Q10 Deficiency-7 (OMIM 616276) results from bi-allelic pathogenic variants in the COQ4 gene. Common clinical findings include hypotonia, seizures, respiratory distress, and cardiomyopathy. In this report, we present two patients diagnosed with Primary Coenzyme Q10 Deficiency-7 along with a review of previously published cases, with the aim being to provide a better understanding of the clinical and laboratory manifestations of the disease.

CASE PRESENTATION

A 3-month-and-22-day-old male was admitted to our outpatient clinic due to poor feeding and restlessness. He was born following an uneventful pregnancy to a nonconsanguineous marriage. A physical examination revealed hypotonia, a dolichocephaly, periorbital edema, and long eyelashes. Blood tests revealed metabolic acidosis and elevated serum lactate levels, while the genetic analysis revealed a variant previously reported as pathogenic, c.437T>G (p.Phe146Cys), in the COQ4 gene. Genetic tests were also conducted on both mother and father, and it revealed heterozygous variant, 0.437T>G (p.Phe146Cys), in the COQ4 gene. As a result of these findings, the patient was diagnosed with neonatal encephalomyopathy-cardiomyopathy-respiratory distress syndrome (Primary Coenzyme Q10 Deficiency-7). A 1-year-old male was admitted to our clinic with complaints of hypotonia, seizures, and feeding difficulties. He was born following an uneventful pregnancy to a nonconsanguineous marriage. On his first day of life, he was admitted to the neonatal intensive care unit due to poor feeding and hypotonia. A physical examination revealed microcephaly, a high palate, poor feeding, weak crying, hypotonia, bilateral horizontal nystagmus, and inability to maintain eye contact. Laboratory findings were within normal limits, while a whole exome sequencing analysis revealed a homozygous variant previously reported as pathogenic, c.458C>T (p.A153V), in the COQ4 gene. The patient was diagnosed with Primary Coenzyme Q10 Deficiency-7.

CONCLUSIONS

Primary Coenzyme Q10 Deficiency-7 should be considered in the differential diagnosis of infants presenting with neurological and dysmorphic manifestations.

Ethnically unique disease burden and limitations of current expanded carrier screening panels

OBJECTIVES

The purpose of the study is to identify the recessive diseases currently affecting real-world pediatric patients in Taiwan, and whether current extended carrier screening panels have the coverage and detective power to identify the pathogenic variants in the carrier parents.

METHODS

A total of 132 trio-samples were collected from May 2017 to March 2022. The participants were parents of pediatric intensive care unit patients who were critically ill or infants with abnormal newborn screening results. A retrospective carrier screening scheme was applied to analyze only the carrier status of pathogenic or likely pathogenic recessive variants resulting in diseases in their children. The recessive disorders diagnosed in our cohort were compared with the gene content in commercial panels.

RESULTS

Mutations in COQ4, PEX1, OTC, and IKBKG were the most frequently identified. In the parents of 44 children with confirmed diagnoses of recessive diseases, 47 (53.40%) screened positive for being the carriers of the same recessive disorders diagnosed in their children. The commercial panels covered 35.13% to 54.05% of the disorders diagnosed in this cohort.

CONCLUSION

Clinicians and genetic counselors should be aware of the limitations of current extended carrier screening and interpret negative screening results with caution. Future panels should also consider genes with ethnically unique mutations such as pathogenic variants of the COQ4 gene in the East Asian population.

Biallelic COQ4 Variants in Hereditary Spastic Paraplegia: Clinical and Molecular Characterization

BACKGROUND

Hereditary spastic paraplegias (HSP) are neurologic disorders characterized by progressive lower-extremity spasticity. Despite the identification of several HSP-related genes, many patients lack a genetic diagnosis.

OBJECTIVES

The aims were to confirm the pathogenic role of biallelic COQ4 mutations in HSP and elucidate the clinical, genetic, and functional molecular features of COQ4-associated HSP.

METHODS

Whole exome sequences of 310 index patients with HSP of unknown cause from three distinct populations were analyzed to identify potential HSP causal genes. Clinical data obtained from patients harboring candidate causal mutations were examined. Functional characterization of COQ4 variants was performed using bioinformatic tools, single-cell RNA sequencing, biochemical assays in cell lines, primary fibroblasts, induced pluripotent stem cell-derived pyramidal neurons, and zebrafish.

RESULTS

Compound heterozygous variants in COQ4, which cosegregated with HSP in pedigrees, were identified in 7 patients from six unrelated families. Patients from four of the six families presented with pure HSP, whereas probands of the other two families exhibited complicated HSP with epilepsy or with cerebellar ataxia. In patient-derived fibroblasts and COQ4 knockout complementation lines, stable expression of these missense variants exerted loss-of-function effects, including mitochondrial reactive oxygen species accumulation, decreased mitochondrial membrane potential, and lower ubiquinone biosynthesis. Whereas differentiated pyramidal neurons expressed high COQ4 levels, coq4 knockdown zebrafish displayed severe motor dysfunction, reflecting motor neuron dysregulation.

CONCLUSIONS

Our study confirms that loss-of-function, compound heterozygous, pathogenic COQ4 variants are causal for autosomal recessive pure and complicated HSP. Moreover, reduced COQ4 levels attributable to variants correspond with decreased ubiquinone biosynthesis, impaired mitochondrial function, and higher phenotypic disease severity. © 2023 International Parkinson and Movement Disorder Society.

Epilepsy and Coenzyme Q10 deficiency with COQ4 variants

Coenzyme Q10 (CoQ10) is one of the essential substances for mitochondrial energy synthesis and extra-mitochondrial vital function. Primary CoQ10 deficiency is a rare disease resulting from interruption of CoQ10 biosynthetic pathway and biallelic COQ4 variants are one of the genetic etiologies recognized in this hereditary disorder. The clinical heterogenicity is broad with wide onset age from prenatal period to adulthood. The typical manifestations include early pharmacoresistant seizure, severe cognition and/or developmental delay, dystonia, ataxia, and spasticity. Patients may also have multisystemic involvements such as cardiomyopathy, lactic acidosis or gastro-esophageal regurgitation disease. Oral CoQ10 supplement is the major therapeutic medication currently. Among those patients, c.370G > A variant is the most common pathogenic variant detected, especially in Asian population. This phenomenon also suggests that this specific allele may be the founder variants in Asia. In this article, we report two siblings with infantile onset seizures, developmental delay, cardiomyopathy, and diffuse brain atrophy. Genetic analysis of both two cases revealed homozygous COQ4 c.370G > A (p.Gly124Ser) variants. We also review the clinical manifestations of primary CoQ10 deficiency patients and possible treatment categories, which are still under survey. As oral CoQ10 supplement may improve or stabilize disease severity, early precise diagnosis of primary CoQ10 deficiency and early treatment are the most important issues. This review article helps to further understand clinical spectrum and treatment categories of primary CoQ10 deficiency with COQ4 variant.

Primary Coenzyme Q10 Deficiency: An Update

Coenzyme Q10 (CoQ10) has a number of vital functions in all cells, both mitochondrial and extra-mitochondrial. In addition to its key role in mitochondrial oxidative phosphorylation, CoQ10 serves as a lipid soluble antioxidant and plays an important role in fatty acid beta-oxidation and pyrimidine and lysosomal metabolism, as well as directly mediating the expression of a number of genes, including those involved in inflammation. Due to the multiplicity of roles in cell function, it is not surprising that a deficiency in CoQ10 has been implicated in the pathogenesis of a wide range of disorders. CoQ10 deficiency is broadly divided into primary and secondary types. Primary CoQ10 deficiency results from mutations in genes involved in the CoQ10 biosynthetic pathway. In man, at least 10 genes are required for the biosynthesis of functional CoQ10, a mutation in any one of which can result in a deficit in CoQ10 status. Patients may respond well to oral CoQ10 supplementation, although the condition must be recognised sufficiently early, before irreversible tissue damage has occurred. In this article, we have reviewed clinical studies (up to March 2023) relating to the identification of these deficiencies, and the therapeutic outcomes of CoQ10 supplementation; we have attempted to resolve the disparities between previous review articles regarding the usefulness or otherwise of CoQ10 supplementation in these disorders. In addition, we have highlighted several of the potential problems relating to CoQ10 supplementation in primary CoQ10 deficiency, as well as identifying unresolved issues relating to these disorders that require further research.

Mitochondrial diseases in Hong Kong: prevalence, clinical characteristics and genetic landscape

OBJECTIVE

To determine the prevalence of mitochondrial diseases (MD) in Hong Kong (HK) and to evaluate the clinical characteristics and genetic landscape of MD patients in the region.

METHODS

This study retrospectively reviewed the phenotypic and molecular characteristics of MD patients from participating public hospitals in HK between January 1985 to October 2020. Molecularly and/or enzymatically confirmed MD cases of any age were recruited via the Clinical Analysis and Reporting System (CDARS) using relevant keywords and/or International Classification of Disease (ICD) codes under the HK Hospital Authority or through the personal recollection of treating clinicians among the investigators.

RESULTS

A total of 119 MD patients were recruited and analyzed in the study. The point prevalence of MD in HK was 1.02 in 100,000 people (95% confidence interval 0.81-1.28 in 100,000). 110 patients had molecularly proven MD and the other nine were diagnosed by OXPHOS enzymology analysis or mitochondrial DNA depletion analysis with unknown molecular basis. Pathogenic variants in the mitochondrial genome (72 patients) were more prevalent than those in the nuclear genome (38 patients) in our cohort. The most commonly involved organ system at disease onset was the neurological system, in which developmental delay, seizures or epilepsy, and stroke-like episodes were the most frequently reported presentations. The mortality rate in our cohort was 37%.

CONCLUSION

This study is a territory-wide overview of the clinical and genetic characteristics of MD patients in a Chinese population, providing the first available prevalence rate of MD in Hong Kong. The findings of this study aim to facilitate future in-depth evaluation of MD and lay the foundation to establish a local MD registry.

Predicting and Understanding the Pathology of Single Nucleotide Variants in Human COQ Genes

Coenzyme Q (CoQ) is a vital lipid that functions as an electron carrier in the mitochondrial electron transport chain and as a membrane-soluble antioxidant. Deficiencies in CoQ lead to metabolic diseases with a wide range of clinical manifestations. There are currently few treatments that can slow or stop disease progression. Primary CoQ₁₀ deficiency can arise from mutations in any of the COQ genes responsible for CoQ biosynthesis. While many mutations in these genes have been identified, the clinical significance of most of them remains unclear. Here we analyzed the structural and functional impact of 429 human missense single nucleotide variants (SNVs) that give rise to amino acid substitutions in the conserved and functional regions of human genes encoding a high molecular weight complex known as the CoQ synthome (or Complex Q), consisting of the COQ3-COQ7 and COQ9 gene products. Using structures of COQ polypeptides, close homologs, and AlphaFold models, we identified 115 SNVs that are potentially pathogenic. Further biochemical characterizations in model organisms such as Saccharomyces cerevisiae are required to validate the pathogenicity of the identified SNVs. Collectively, our results will provide a resource for clinicians during patient diagnosis and guide therapeutic efforts toward combating primary CoQ₁₀ deficiency.

Human COQ4 deficiency: delineating the clinical, metabolic and neuroimaging phenotypes

BACKGROUND

Human coenzyme Q4 (COQ4) is essential for coenzyme Q₁₀ (CoQ₁₀) biosynthesis. Pathogenic variants in COQ4 cause childhood-onset neurodegeneration. We aimed to delineate the clinical spectrum and the cellular consequences of COQ4 deficiency.

METHODS

Clinical course and neuroradiological findings in a large cohort of paediatric patients with COQ4 deficiency were analysed. Functional studies in patient-derived cell lines were performed.

RESULTS

We characterised 44 individuals from 36 families with COQ4 deficiency (16 newly described). A total of 23 different variants were identified, including four novel variants in COQ4. Correlation analyses of clinical and neuroimaging findings revealed three disease patterns: type 1: early-onset phenotype with neonatal brain anomalies and epileptic encephalopathy; type 2: intermediate phenotype with distinct stroke-like lesions; and type 3: moderate phenotype with non-specific brain pathology and a stable disease course. The functional relevance of COQ4 variants was supported by in vitro studies using patient-derived fibroblast lines. Experiments revealed significantly decreased COQ4 protein levels, reduced levels of cellular CoQ₁₀ and elevated levels of the metabolic intermediate 6-demethoxyubiquinone.

CONCLUSION

Our study describes the heterogeneous clinical presentation of COQ4 deficiency and identifies phenotypic subtypes. Cell-based studies support the pathogenic characteristics of COQ4 variants. Due to the insufficient clinical response to oral CoQ₁₀ supplementation, alternative treatment strategies are warranted.

Expanding the clinical spectrum of primary coenzyme Q10 deficiency type 6: The first case with cardiomyopathy

We report a 19-month-old patient with cardiomyopathy as the first presenting feature of primary COQ10 deficiency-6. This case expands the phenotypic spectrum of this disorder. Furthermore, it shows that genetic testing for primary COQ10 deficiency should be considered in patients with pediatric-onset cardiomyopathy as it can guide treatment options.

A novel COQ7 mutation causing primarily neuromuscular pathology and its treatment options

Coenzyme Q₁₀ (CoQ₁₀) is necessary as electron transporter in mitochondrial respiration and other cellular functions. CoQ₁₀ is synthesized by all cells and defects in the synthesis pathway result in primary CoQ₁₀ deficiency that frequently leads to severe mitochondrial disease syndrome. CoQ₁₀ is exceedingly hydrophobic, insoluble, and poorly bioavailable, with the result that dietary CoQ₁₀ supplementation produces no or only minimal relief for patients. We studied a patient from Turkey and identified and characterized a new mutation in the CoQ₁₀ biosynthetic gene COQ7 (c.161G > A; p.Arg54Gln). We find that unexpected neuromuscular pathology can accompany CoQ₁₀ deficiency caused by a COQ7 mutation. We also show that by-passing the need for COQ7 by providing the unnatural precursor 2,4-dihydroxybenzoic acid, as has been proposed, is unlikely to be an effective and safe therapeutic option. In contrast, we show for the first time in human patient cells that the respiratory defect resulting from CoQ₁₀ deficiency is rescued by providing CoQ₁₀ formulated with caspofungin (CF/CoQ). Caspofungin is a clinically approved intravenous fungicide whose surfactant properties lead to CoQ₁₀ micellization, complete water solubilization, and efficient uptake by cells and organs in animal studies. These findings reinforce the possibility of using CF/CoQ in the clinical treatment of CoQ₁₀-deficient patients.

Primary Coenzyme Q10 Deficiency-7 and Pathogenic COQ4 Variants: Clinical Presentation, Biochemical Analyses, and Treatment

Primary Coenzyme Q10 Deficiency-7 (COQ10D7) is a rare mitochondrial disorder caused by pathogenic COQ4 variants. In this review, we discuss the correlation of COQ4 genotypes, particularly the East Asian-specific c.370G > A variant, with the clinical presentations and therapeutic effectiveness of coenzyme Q10 supplementation from an exon-dependent perspective. Pathogenic COQ4 variants in exons 1–4 are associated with less life-threating presentations, late onset, responsiveness to CoQ10 therapy, and a relatively long lifespan. In contrast, pathogenic COQ4 variants in exons 5–7 are associated with early onset, unresponsiveness to CoQ10 therapy, and early death and are more fatal. Patients with the East Asian-specific c.370G > A variant displays intermediate disease severity with multi-systemic dysfunction, which is between that of the patients with variants in exons 1–4 and 5–7. The mechanism underlying this exon-dependent genotype-phenotype correlation may be associated with the structure and function of COQ4. Sex is shown unlikely to be associated with disease severity. While point-of-care high-throughput sequencing would be useful for the rapid diagnosis of pathogenic COQ4 variants, whereas biochemical analyses of the characteristic impairments in CoQ10 biosynthesis and mitochondrial respiratory chain activity, as well as the phenotypic rescue of the CoQ10 treatment, are necessary to confirm the pathogenicity of suspicious variants. In addition to CoQ10 derivatives, targeted drugs and gene therapy could be useful treatments for COQ10D7 depending on the in-depth functional investigations and the development of gene editing technologies. This review provides a fundamental reference for the sub-classification of COQ10D7 and aim to advance our knowledge of the pathogenesis, clinical diagnosis, and prognosis of this disease and possible interventions.

Coenzyme Q10 effects in neurological diseases

Coenzyme Q10 (CoQ10), a lipophilic substituted benzoquinone, is present in animal and plant cells. It is endogenously synthetized in every cell and involved in a variety of cellular processes. CoQ10 is an obligatory component of the respiratory chain in inner mitochondrial membrane. In addition, the presence of CoQ10 in all cellular membranes and in blood. It is the only endogenous lipid antioxidant. Moreover, it is an essential factor for uncoupling protein and controls the permeability transition pore in mitochondria. It also participates in extramitochondrial electron transport and controls membrane physicochemical properties. CoQ10 effects on gene expression might affect the overall metabolism. Primary changes in the energetic and antioxidant functions can explain its remedial effects. CoQ10 supplementation is safe and well-tolerated, even at high doses. CoQ10 does not cause any serious adverse effects in humans or experimental animals. New preparations of CoQ10 that are less hydrophobic and structural derivatives, like idebenone and MitoQ, are being developed to increase absorption and tissue distribution. The review aims to summarize clinical and experimental effects of CoQ10 supplementations in some neurological diseases such as migraine, Parkinson´s disease, Huntington´s disease, Alzheimer´s disease, amyotrophic lateral sclerosis, Friedreich´s ataxia or multiple sclerosis. Cardiovascular hypertension was included because of its central mechanisms controlling blood pressure in the brainstem rostral ventrolateral medulla and hypothalamic paraventricular nucleus. In conclusion, it seems reasonable to recommend CoQ10 as adjunct to conventional therapy in some cases. However, sometimes CoQ10 supplementations are more efficient in animal models of diseases than in human patients (e.g. Parkinson´s disease) or rather vague (e.g. Friedreich´s ataxia or amyotrophic lateral sclerosis).

Coenzyme Q at the Hinge of Health and Metabolic Diseases

Coenzyme Q is a unique lipidic molecule highly conserved in evolution and essential to maintaining aerobic metabolism. It is endogenously synthesized in all cells by a very complex pathway involving a group of nuclear genes that share high homology among species. This pathway is tightly regulated at transcription and translation, but also by environment and energy requirements. Here, we review how coenzyme Q reacts within mitochondria to promote ATP synthesis and also integrates a plethora of metabolic pathways and regulates mitochondrial oxidative stress. Coenzyme Q is also located in all cellular membranes and plasma lipoproteins in which it exerts antioxidant function, and its reaction with different extramitochondrial oxidoreductases contributes to regulate the cellular redox homeostasis and cytosolic oxidative stress, providing a key factor in controlling various apoptosis mechanisms. Coenzyme Q levels can be decreased in humans by defects in the biosynthesis pathway or by mitochondrial or cytosolic dysfunctions, leading to a highly heterogeneous group of mitochondrial diseases included in the coenzyme Q deficiency syndrome. We also review the importance of coenzyme Q levels and its reactions involved in aging and age-associated metabolic disorders, and how the strategy of its supplementation has had benefits for combating these diseases and for physical performance in aging.

Cellular Models for Primary CoQ Deficiency Pathogenesis Study

Primary coenzyme Q₁₀ (CoQ) deficiency includes a heterogeneous group of mitochondrial diseases characterized by low mitochondrial levels of CoQ due to decreased endogenous biosynthesis rate. These diseases respond to CoQ treatment mainly at the early stages of the disease. The advances in the next generation sequencing (NGS) as whole-exome sequencing (WES) and whole-genome sequencing (WGS) have increased the discoveries of mutations in either gene already described to participate in CoQ biosynthesis or new genes also involved in this pathway. However, these technologies usually provide many mutations in genes whose pathogenic effect must be validated. To functionally validate the impact of gene variations in the disease’s onset and progression, different cell models are commonly used. We review here the use of yeast strains for functional complementation of human genes, dermal skin fibroblasts from patients as an excellent tool to demonstrate the biochemical and genetic mechanisms of these diseases and the development of human-induced pluripotent stem cells (hiPSCs) and iPSC-derived organoids for the study of the pathogenesis and treatment approaches.

Neuromitochondrial Disorders : Genomic Basis and an Algorithmic Approach to Imaging Diagnostics

Mitochondrial disorders have been an enigma for a long time due to the varied clinical presentations. Although a genetic confirmation will be mandatory most of the time, half the number of Leigh syndrome would be negative for genetic mutations. There are a growing number of mutations in clinical practice, which escape detection on routine clinical exome sequencing. Imaging would render help in pointing towards a mitochondrial disorder. There are a few case reports which brief about specific mitochondrial mutations and their specific imaging appearance. This article tries to provide a comprehensive review on the imaging-genomic correlation of mitochondrial disorders with an objective of performing a specific genetic testing to arrive at an accurate diagnosis.

The Role of Mitochondrial Dysfunction in Vascular Disease, Tumorigenesis, and Diabetes

Mitochondrial dysfunction is known to be associated with a wide range of human pathologies, such as cancer, metabolic, and cardiovascular diseases. One of the possible ways of mitochondrial involvement in the cellular damage is excessive production of reactive oxygen and nitrogen species (ROS and RNS) that cannot be effectively neutralized by existing antioxidant systems. In mitochondria, ROS and RNS can contribute to protein and mitochondrial DNA (mtDNA) damage causing failure of enzymatic chains and mutations that can impair mitochondrial function. These processes further lead to abnormal cell signaling, premature cell senescence, initiation of inflammation, and apoptosis. Recent studies have identified numerous mtDNA mutations associated with different human pathologies. Some of them result in imbalanced oxidative phosphorylation, while others affect mitochondrial protein synthesis. In this review, we discuss the role of mtDNA mutations in cancer, diabetes, cardiovascular diseases, and atherosclerosis. We provide a list of currently described mtDNA mutations associated with each pathology and discuss the possible future perspective of the research.

Primary Coenzyme Q deficiencies: A literature review and online platform of clinical features to uncover genotype-phenotype correlations

Primary Coenzyme Q (CoQ) deficiencies are clinically heterogeneous conditions and lack clear genotype-phenotype correlations, complicating diagnosis and prognostic assessment. Here we present a compilation of all the symptoms and patients with primary CoQ deficiency described in the literature so far and analyse the most common clinical manifestations associated with pathogenic variants identified in the different COQ genes. In addition, we identified new associations between the age of onset of symptoms and different pathogenic variants, which could help to a better diagnosis and guided treatment. To make these results useable for clinicians, we created an online platform (https://coenzymeQbiology.github.io/clinic-CoQ-deficiency) about clinical manifestations of primary CoQ deficiency that will be periodically updated to incorporate new information published in the literature. Since CoQ primary deficiency is a rare disease, the available data are still limited, but as new patients are added over time, this tool could become a key resource for a more efficient diagnosis of this pathology.

New pathogenic variants in COQ4 cause ataxia and neurodevelopmental disorder without detectable CoQ10 deficiency in muscle or skin fibroblasts

COQ4 is a component of an enzyme complex involved in the biosynthesis of coenzyme Q₁₀ (CoQ₁₀), a molecule with primary importance in cell metabolism. Mutations in the COQ4 gene are responsible for mitochondrial diseases showing heterogeneous age at onset, clinical presentations and association with CoQ₁₀ deficiency. We herein expand the phenotypic and genetic spectrum of COQ4-related diseases, by reporting two patients harboring bi-allelic variants but not showing CoQ₁₀ deficiency. One patient was found to harbor compound heterozygous mutations (specifically, c.577C>T/p.Pro193Ser and the previously reported c.718C>T/p.Arg240Cys) associated with progressive spasticity, while the other harbored two novel missense (c.284G>A/p.Gly95Asp and c.305G>A/p.Arg102His) associated with a neurodevelopmental disorder. Both patients presented motor impairment and ataxia. To further understand the role of COQ4, we performed functional studies in patient-derived fibroblasts, yeast and "crispant" zebrafish larvae. Micro-oxygraphy showed impaired oxygen consumption rates in one patient, while yeast complementation assays showed that all the mutations were presumably disease related. Moreover, characterization of the coq4 F0 CRISPR zebrafish line showed motor defects and cell reduction in a specific area of the hindbrain, a region reminiscent of the human cerebellum. Our expanded phenotype associated with COQ4 mutations allowed us to investigate, for the first time, the role of COQ4 in brain development in vivo.

Delineation of molecular findings by whole-exome sequencing for suspected cases of paediatric-onset mitochondrial diseases in the Southern Chinese population

BACKGROUND

Mitochondrial diseases (MDs) are a group of clinically and genetically heterogeneous disorders characterized by defects in oxidative phosphorylation. Since clinical phenotypes of MDs may be non-specific, genetic diagnosis is crucial for guiding disease management. In the current study, whole-exome sequencing (WES) was performed for our paediatric-onset MD cohort of a Southern Chinese origin, with the aim of identifying key disease-causing variants in the Chinese patients with MDs.

METHODS

We recruited Chinese patients who had paediatric-onset MDs and a minimum mitochondrial disease criteria (MDC) score of 3. Patients with positive target gene or mitochondrial DNA sequencing results were excluded. WES was performed, variants with population frequency ≤ 1% were analysed for pathogenicity on the basis of the American College of Medical Genetics and Genomics guidelines.

RESULTS

Sixty-six patients with pre-biopsy MDC scores of 3-8 were recruited. The overall diagnostic yield was 35% (23/66). Eleven patients (17%) were found to have mutations in MD-related genes, with COQ4 having the highest mutation rate owing to the Chinese-specific founder mutation (4/66, 6%). Twelve patients (12/66, 18%) had mutations in non-MD-related genes: ATP1A3 (n = 3, two were siblings), ALDH5A1, ARX, FA2H, KCNT1, LDHD, NEFL, NKX2-2, TBCK, and WAC.

CONCLUSIONS

We confirmed that the COQ4:c.370G>A, p.(Gly124Ser) variant, was a founder mutation among the Southern Chinese population. Screening for this mutation should therefore be considered while diagnosing Chinese patients suspected to have MDs. Furthermore, WES has proven to be useful in detecting variants in patients suspected to have MDs because it helps to obtain an unbiased and precise genetic diagnosis for these diseases, which are genetically heterogeneous.

Primary coenzyme Q10 deficiency due to COQ8A gene mutations

BACKGROUND

Primary deficiency of coenzyme Q10 deficiency-4 (COQ10D4) is an autosomal recessive cerebellar ataxia with mitochondrial respiratory chain disfunction. The main clinical manifestation involves early-onset exercise intolerance, progressive cerebellar ataxia, and movement disorders. COQ8A gene mutations are responsible for this disease. Here, we provide clinical, laboratory, and genetic findings of a patient with cerebellar ataxia caused by compound heterozygous mutations in COQ8A gene.

METHODS

A male patient from a non-consanguineous Chinese family underwent detailed physical and auxiliary examination. After exclusion of acquired causes of ataxia, Friedreich's Ataxia, and common types of spinocerebellar ataxia, the patient was subjected to whole exome sequencing (WES) followed by confirmation of sequence variants using Sanger sequencing. His asymptomatic parents, two brothers and one sister were genotyped for these variants.

RESULTS

This patient showed early-onset exercise intolerance and progressive cerebellar ataxia, wide-based gait and tremor, accompanied by symptoms of dysautonomia. His serum lactate level was elevated and plasma total Coenzyme Q10 (CoQ10) was decreased. Brain MRI showed cerebellar atrophy, and X-ray of the spine revealed thoraco-lumbar scoliosis. Compound heterozygous mutations in the COQ8A gene were identified through WES: c.1844_1845insG, p.Ser616Leufs*114 and c.902G>A, p.Arg301Gln. After treatment with ubidecarenone, 40 mg three times per day for 2 years, the symptoms dramatically improved.

CONCLUSIONS

We identified a patient with COQ10D4 caused by novel COQ8A mutations. Our findings widen the spectrum of COQ8A gene mutations and clinical manifestations.

Rapid whole-exome sequencing facilitates precision medicine in paediatric rare disease patients and reduces healthcare costs

Background

Rapid whole-exome sequencing (rWES) offers the potential for early diagnosis-predicated precision medicine. Previous evidence focused predominantly on infants from the intensive care unit (ICU). This study sought to examine the diagnostic and clinical utility, and the economic impact on clinical management of rWES in patients beyond infancy and ICU setting.

Methods

rWES was performed on a prospective cohort of patients with suspected monogenic disorder referred from territory-wide paediatric ICUs and non-ICUs in Hong Kong urging for rapid genetic diagnosis. All eligible families were invited. We aimed to achieve a rapid turnaround time (TAT) of 14 days. Clinical utility and costs associated with clinical management were assessed in diagnosed cases. Actual quantitative changes in healthcare utilisation were compared with a counterfactual diagnostic trajectory and/or with matched historical control whenever possible.

Findings

rWES were offered to 102 families and 32/102 (31%) patients received a molecular diagnosis, with a median TAT of 11 days. Clinical management changed in 28 of 32 diagnosed patients (88%), including but not limited to modifications in treatment, avoidance of surgeries, and informing decisions on redirection of care. Cost analysis was performed in eight patients. rWES was estimated to reduce hospital length of stay by 566 days and decrease healthcare costs by HKD$8,044,250 (GBP£796,460) for these eight patients. The net cost-savings after inclusion of rWES costs were estimated to be HKD$5,325,187 (GBP£527,246).

Interpretation

This study replicates the diagnostic capacity and rapid TAT of rWES in predominantly Chinese patients, and demonstrates diagnosis-predicated precision medicine and net healthcare savings. Findings were corroborated by evidence from multinational cohorts, combined as part of a meta-analysis. rWES merits consideration as a first-tier diagnostic tool for patients with urgent needs in the clinical setting.

Funding

Health and Medical Research Fund, HKU Seed Fund for Basic Research, The Society for the Relief of Disabled Children, and Edward and Yolanda Wong Fund.

The KLHL40 c.1516A>C is a Chinese-specific founder mutation causing nemaline myopathy 8: Report of six patients with pre- and postnatal phenotypes

Background

Autosomal recessive or compound heterozygous mutations in KLHL40 cause nemaline myopathy 8, which is one of the most severe forms of nemaline myopathy. The KLHL40 c.1516A>C variant has recently been reported as a founder mutation in southern Chinese.

Methods

We report six cases of nemaline myopathy 8 which involves the c.1516A>C variant, from five unrelated families of non‐consanguineous southern Chinese. The pre‐ and postnatal phenotypes of these cases were reviewed with emphasis on prenatal clinical features. Genetic testing for the founder mutation was performed on three patients with homozygous mutations.

Results

Common prenatal features included reduced fetal movement, polyhydramnios, breech presentation, and clubfeet. Two pregnancies were terminated. Four live‐born patients had postnatal features typical of nemaline myopathy 8. The length of survival ranged from 49 days to 17 months, with respiratory failure and infections being the principal causes of death. Haplotype analysis in three patients with homozygous mutation showed a shared haplotype block of 1.1727 cM spanning over the c.1516A>C variant, suggesting it is a southern Chinese‐specific founder mutation.

Conclusion

Analysis of the KLHL40 c.1516A>C variant should be considered in prenatal diagnosis of Chinese pregnant patients with suspected congenital neuromuscular disorders or with significant family history of congenital myopathies.

Redefining infantile-onset multisystem phenotypes of coenzyme Q10-deficiency in the next-generation sequencing era

Primary coenzyme Q₁₀ (CoQ₁₀) deficiency encompasses a subset of mitochondrial diseases caused by mutations affecting proteins involved in the CoQ₁₀ biosynthetic pathway. One of the most frequent clinical syndromes associated with primary CoQ₁₀ deficiency is the severe infantile multisystemic form, which, until recently, was underdiagnosed. In the last few years, the availability of genetic screening through whole exome sequencing and whole genome sequencing has enabled molecular diagnosis in a growing number of patients with this syndrome and has revealed new disease phenotypes and molecular defects in CoQ₁₀ biosynthetic pathway genes. Early genetic screening can rapidly and non-invasively diagnose primary CoQ₁₀ deficiencies. Early diagnosis is particularly important in cases of CoQ₁₀ deficient steroid-resistant nephrotic syndrome, which frequently improves with treatment. In contrast, the infantile multisystemic forms of CoQ₁₀ deficiency, particularly when manifesting with encephalopathy, present therapeutic challenges, due to poor responses to CoQ₁₀ supplementation. Administration of CoQ₁₀ biosynthetic intermediate compounds is a promising alternative to CoQ₁₀; however, further pre-clinical studies are needed to establish their safety and efficacy, as well as to elucidate the mechanism of actions of the intermediates. Here, we review the molecular defects causes of the multisystemic infantile phenotype of primary CoQ₁₀ deficiency, genotype-phenotype correlations, and recent therapeutic advances.