Coenzyme Q10-responsive ataxia: 2-year-treatment follow-up

Primary Coenzyme Q10 Deficiency-Related Ataxias

Cerebellar ataxia is a neurological syndrome characterized by the imbalance (e.g., truncal ataxia, gait ataxia) and incoordination of limbs while executing a task (dysmetria), caused by the dysfunction of the cerebellum or its connections. It is frequently associated with other signs of cerebellar dysfunction, including abnormal eye movements, dysmetria, kinetic tremor, dysarthria, and/or dysphagia. Among the so-termed mitochondrial ataxias, variants in genes encoding steps of the coenzyme Q10 biosynthetic pathway represent a common cause of autosomal recessive primary coenzyme Q10 deficiencies (PCoQD)s. PCoQD is a potentially treatable condition; therefore, a correct and timely diagnosis is essential. After a brief presentation of the illustrative case of an Italian woman with this condition (due to a novel homozygous nonsense mutation in COQ8A), this article will review ataxias due to PCoQD.

Mutations of GEMIN5 are associated with coenzyme Q10 deficiency: long-term follow-up after treatment

GEMIN5 exerts key biological functions regulating pre-mRNAs intron removal to generate mature mRNAs. A series of patients were reported harboring mutations in GEMIN5. No treatments are currently available for this disease. We treated two of these patients with oral Coenzyme Q10 (CoQ10), which resulted in neurological improvements, although MRI abnormalities remained. Whole Exome Sequencing demonstrated compound heterozygosity at the GEMIN5 gene in both cases: Case one: p.Lys742* and p.Arg1016Cys; Case two: p.Arg1016Cys and p.Ser411Hisfs*6. Functional studies in fibroblasts revealed a decrease in CoQ10 biosynthesis compared to controls. Supplementation with exogenous CoQ10 restored it to control intracellular CoQ10 levels. Mitochondrial function was compromised, as indicated by the decrease in oxygen consumption, restored by CoQ10 supplementation. Transcriptomic analysis of GEMIN5 patients compared with controls showed general repression of genes involved in CoQ10 biosynthesis. In the rigor mortis defective flies, CoQ10 levels were decreased, and CoQ10 supplementation led to an improvement in the adult climbing assay performance, a reduction in the number of motionless flies, and partial restoration of survival. Overall, we report the association between GEMIN5 dysfunction and CoQ10 deficiency for the first time. This association opens the possibility of oral CoQ10 therapy, which is safe and has no observed side effects after long-term therapy.

Whole-Exome Sequencing Study of Fibroblasts Derived From Patients With Cerebellar Ataxia Referred to Investigate CoQ10 Deficiency

Background and Objectives

Coenzyme Q10(CoQ10)–deficient cerebellar ataxia can be due to pathogenic variants in genes encoding for CoQ10biosynthetic proteins or associated with defects in protein unrelated to its biosynthesis. Diagnosis is crucial because patients may respond favorably to CoQ10supplementation. The aim of this study was to identify through whole-exome sequencing (WES) the pathogenic variants, and assess CoQ10levels, in fibroblasts from patients with undiagnosed cerebellar ataxia referred to investigate CoQ10deficiency.

Methods

WES was performed on genomic DNA extracted from 16 patients. Sequencing data were filtered using a virtual panel of genes associated with CoQ10deficiency and/or cerebellar ataxia. CoQ10levels were measured by high-performance liquid chromatography in 14 patient-derived fibroblasts.

Results

A definite genetic etiology was identified in 8 samples of 16 (diagnostic yield = 50%). The identified genetic causes were pathogenic variants of the genesCOQ8A(ADCK3) (n = 3 samples),ATP1A3(n = 2),PLA2G6(n = 1),SPG7(n = 1), andMFSD8(n = 1). Five novel mutations were found (COQ8An = 3,PLA2G6n = 1, andMFSD8n = 1). CoQ10levels were significantly decreased in 3/14 fibroblast samples (21.4%), 1 carrying compound heterozygousCOQ8Apathogenic variants, 1 harboring a homozygous pathogenicSPG7variant, and 1 with an unknown molecular defect.

Discussion

This work confirms the importance ofCOQ8Agene mutations as a frequent genetic cause of cerebellar ataxia and CoQ10deficiency and suggestsSPG7mutations as a novel cause of secondary CoQ10deficiency.

Beneficial antioxidant effects of Coenzyme Q10 on reproduction

This chapter focuses on preclinical and clinical studies conducted in recent years that contribute to increasing knowledge on the role of Coenzyme Q10 in female reproductive health. General aspects of CoQ10, such as its role as an antioxidant and in mitochondrial bioenergetics are considered. The age-dependent decline in human female reproductive potential is associated with cellular mitochondrial dysfunction and oxidative stress, and in some cases accompanied by a decrease in CoQ10 levels. Herein, we discuss experimental and clinical evidence on CoQ10 protective effects on reproductive health. We also address the potential of supplementation with this coenzyme to rescue reprotoxicity induced by exposure to environmental xenobiotics. This review not only contributes to our general understanding of the effects of aging on female reproduction but also provides new insights into strategies promoting reproductive health. The use of CoQ10 supplementation can improve reproductive performance through the scavenging of reactive oxygen species and free radicals. This strategy can constitute a low-risk and low-cost strategy to attenuate the impact on fertility related to aging and exposure to environmental chemicals.

Treatable cerebellar ataxias

Cerebellar ataxic syndrome is a heterogenous class of disorders which can result from a miscellany of causes- genetic or acquired. There are a few metabolic, immune mediated, inflammatory and hereditary causes of ataxia which can be diagnosed from the gamut of possibilities, offering great relief to the ailing patient, their family and the treating physician. A pragmatic algorithm for diagnosing treatable causes of ataxia includes a thorough clinical history, meticulous examination for associated signs and an investigative mind to clinch the diagnosis. With novel diagnostic techniques and targeted therapies, early diagnosis and treatment can lead to favourable outcomes. In this review, diseases presenting predominantly as cerebellar ataxia and are treatable by targeted therapies are discussed.

Vitamin K2 cannot substitute Coenzyme Q10 as electron carrier in the mitochondrial respiratory chain of mammalian cells

Coenzyme Q₁₀ (CoQ₁₀) deficiencies are a group of heterogeneous conditions that respond to ubiquinone administration if treated soon after the onset of symptoms. However, this treatment is only partially effective due to its poor bioavailability. We tested whether vitamin K2, which was reported to act as a mitochondrial electron carrier in D. melanogaster, could mimic ubiquinone function in human CoQ₁₀ deficient cell lines, and in yeast carrying mutations in genes required for coenzyme Q₆ (CoQ₆) biosynthesis. We found that vitamin K2, despite entering into mitochondria, restored neither electron flow in the respiratory chain, nor ATP synthesis. Conversely, coenzyme Q₄ (CoQ₄), an analog of CoQ₁₀ with a shorter isoprenoid side chain, could efficiently substitute its function. Given its better solubility, CoQ₄ could represent an alternative to CoQ₁₀ in patients with both primary and secondary CoQ₁₀ deficiencies.

The Comprehensive Management of Cerebellar Ataxia in Adults

PURPOSE OF REVIEW

In this review, we present the multidisciplinary approach to the management of the many neurological, medical, social, and emotional issues facing patients with cerebellar ataxia.

RECENT FINDINGS

Our holistic approach to treatment, developed over the past 25 years in the Massachusetts General Hospital Ataxia Unit, is centered on the compassionate care of the patient and their family, empowering them through engagement, and including the families as partners in the healing process. We present the management of ataxia in adults, beginning with establishing an accurate diagnosis, followed by treatment of the multiple symptoms seen in cerebellar disorders, with a view to maximizing quality of life and effectively living with the consequences of ataxia. We discuss the importance of a multidisciplinary approach to the management of ataxia, including medical and non-medical management and the evidence base that supports these interventions. We address the pharmacological treatment of ataxia, tremor, and other associated movement disorders; ophthalmological symptoms; bowel, bladder, and sexual symptoms; orthostatic hypotension; psychiatric and cognitive symptoms; neuromodulation, including deep brain stimulation; rehabilitation including physical therapy, occupational therapy and speech and language pathology and, as necessary, involving urology, psychiatry, and pain medicine. We discuss the role of palliative care in late-stage disease. The management of adults with ataxia is complex and a team-based approach is essential.

ADCK3-related Coenzyme Q10 Deficiency: A Potentially Treatable Genetic Disease

Background

Disorders related to dysfunction of coenzyme (CoQ₁₀) metabolism, including AarF domain containing kinase 3 gene (ADCK3) mutations, have received attention due to the potential for response to CoQ₁₀ supplementation.

Methods

We describe two new cases of neurological syndromes due to ADCK3 mutations that obtained striking benefit from CoQ10, and a third who did not. We also review 20 cases from the literature in which responses to CoQ10 were documented out of all 38 previously reported cases.

Results

Despite the remarkable responses in some cases with ataxia and movement disorders (myoclonus, dystonia, tremor), overall, we were not able to identify variables that predicted response to CoQ₁₀ supplementation.

Conclusions

Based on our experience and data from the literature, we recommend a minimum of 10 mg/kg/day of ubiquinone with titration up to 15 mg/kg/day, maintained at least for 6 months in order to obtain or exclude potential benefit from therapy.

Molecular diagnosis of coenzyme Q10 deficiency: an update

INTRODUCTION

Coenzyme Q₁₀ (CoQ) deficiency syndromes comprise a growing number of genetic disorders. While primary CoQ deficiency syndromes are rare diseases, secondary deficiencies have been related to both genetic and environmental conditions, which are the main causes of biochemical CoQ deficiency. The diagnosis is the essential first step for planning future treatment strategies, as the potential treatability of CoQ deficiency is the most critical issue for the patients. Areas covered: While the quickest and most effective tool to define a CoQ-deficient status is its biochemical determination in biological fluids or tissues, this quantification does not provide a definite diagnosis of a CoQ-deficient status nor insight about the genetic etiology of the disease. The different laboratory tests to check for CoQ deficiency are evaluated in order to choose the best diagnostic pathway for the patient. Expert commentary: New insights are being discovered about the implication of new proteins in the intricate CoQ biosynthetic pathway. These insights reinforce the idea that next generation sequencing diagnostic strategies are the unique alternative in terms of rapid and accurate molecular diagnosis of CoQ deficiency.

Three-Year Follow-Up of High-Dose Ubiquinol Supplementation in a Case of Familial Multiple System Atrophy with Compound Heterozygous COQ2 Mutations

We report a 3-year follow-up of high-dose ubiquinol supplementation in a case of familial multiple system atrophy (MSA) with compound heterozygous nonsense (R387X) and missense (V393A) mutations in COQ2. A high-dose ubiquinol supplementation substantially increased total coenzyme Q₁₀ levels in cerebrospinal fluid as well as in plasma. The patient was at the advanced stage of MSA, and the various scores of clinical rating scales remained stable without changes during the 3 years. The cerebral metabolic ratio of oxygen measured by ¹⁵O₂ PET, however, increased by approximately 30% after administration of ubiquinol, suggesting that ubiquinol can improve mitochondrial oxidative metabolism in the brain. It also suggests the therapeutic potential of ubiquinol for patients with MSA with COQ2 mutations. Further clinical trials of administration of high-dose ubiquinol to MSA patients are warranted.

Coenzyme Q10 Supplementation in Aging and Disease

Coenzyme Q (CoQ) is an essential component of the mitochondrial electron transport chain and an antioxidant in plasma membranes and lipoproteins. It is endogenously produced in all cells by a highly regulated pathway that involves a mitochondrial multiprotein complex. Defects in either the structural and/or regulatory components of CoQ complex or in non-CoQ biosynthetic mitochondrial proteins can result in a decrease in CoQ concentration and/or an increase in oxidative stress. Besides CoQ₁₀ deficiency syndrome and aging, there are chronic diseases in which lower levels of CoQ₁₀ are detected in tissues and organs providing the hypothesis that CoQ₁₀ supplementation could alleviate aging symptoms and/or retard the onset of these diseases. Here, we review the current knowledge of CoQ₁₀ biosynthesis and primary CoQ₁₀ deficiency syndrome, and have collected published results from clinical trials based on CoQ₁₀ supplementation. There is evidence that supplementation positively affects mitochondrial deficiency syndrome and the symptoms of aging based mainly on improvements in bioenergetics. Cardiovascular disease and inflammation are alleviated by the antioxidant effect of CoQ₁₀. There is a need for further studies and clinical trials involving a greater number of participants undergoing longer treatments in order to assess the benefits of CoQ₁₀ treatment in metabolic syndrome and diabetes, neurodegenerative disorders, kidney diseases, and human fertility.

Scales for the clinical evaluation of cerebellar disorders

Clinical scales represent an important tool not only for the initial grading/scoring of disease and assessment of progression, but also for the quantification of therapeutic effects in clinical trials. There are several scales available for the clinical evaluation of cerebellar symptoms. While some scales have been developed and evaluated for specific cerebellar disorders such as Friedreich ataxia, others reliably capture cerebellar symptoms with no respect to the underlying etiology. Each scale has its strengths and weaknesses. Extensive scales are certainly useful for thorough documentation of specific features of certain phenotypes, but this gain of information is not always essential for the purpose of a study. Therefore, compact and manageable scales like the Scale for the Assessment and Rating of Ataxia (SARA) or Brief Ataxia Rating Scale (BARS) are often preferred compared to more complex scales in observational and therapeutic studies.

A novel inborn error of the coenzyme Q10 biosynthesis pathway: cerebellar ataxia and static encephalomyopathy due to COQ5 C-methyltransferase deficiency

Primary coenzyme Q10 (CoQ10 ; MIM# 607426) deficiencies are an emerging group of inherited mitochondrial disorders with heterogonous clinical phenotypes. Over a dozen genes are involved in the biosynthesis of CoQ10 , and mutations in several of these are associated with human disease. However, mutations in COQ5 (MIM# 616359), catalyzing the only C-methylation in the CoQ10 synthetic pathway, have not been implicated in human disease. Here, we report three female siblings of Iraqi-Jewish descent, who had varying degrees of cerebellar ataxia, encephalopathy, generalized tonic-clonic seizures, and cognitive disability. Whole-exome and subsequent whole-genome sequencing identified biallelic duplications in the COQ5 gene, leading to reduced levels of CoQ10 in peripheral white blood cells of all affected individuals and reduced CoQ10 levels in the only muscle tissue available from one affected proband. CoQ10 supplementation led to clinical improvement and increased the concentrations of CoQ10 in blood. This is the first report of primary CoQ10 deficiency caused by loss of function of COQ5, with delineation of the clinical, laboratory, histological, and molecular features, and insights regarding targeted treatment with CoQ10 supplementation.

Age-related reference values for the pediatric Scale for Assessment and Rating of Ataxia: a multicentre study

AIM

For reliable assessment of ataxia severity in children, the Childhood Ataxia and Cerebellar Group of the European Pediatric Neurology Society aimed to validate the Scale for Assessment and Rating of Ataxia (SARA) according to age.

METHOD

Twenty-two pediatric ataxia experts from 15 international institutions scored videotaped SARA performances in 156 typically developing children (4-16y: m/f=1; 12 children per year of age; including nine different nationalities). We determined age-dependency and reliability of pediatric SARA scores by a mixed model.

RESULTS

In typically developing children, age was the only variable that revealed a relationship with SARA scores (p<0.001). The youngest children revealed the highest scores and the highest variation in scores (<8y; p<0.001). After 11 years of age, pediatric scores approached adult outcomes. The interobserver agreement of total SARA scores was substantial with an intraclass correlation coefficient of 0.63 (95% confidence interval 0.56-0.69; p<0.001).

INTERPRETATION

In typically developing European children, both SARA scores and interobserver agreement are age-dependent. For reliable interpretation of pediatric SARA scores, consideration of the underlying test construct appears prudent. These data will hopefully contribute to a correct and uniform interpretation of longitudinal SARA scores from childhood to adulthood.

Biochemical Assessment of Coenzyme Q10 Deficiency

Coenzyme Q₁₀ (CoQ₁₀) deficiency syndrome includes clinically heterogeneous mitochondrial diseases that show a variety of severe and debilitating symptoms. A multiprotein complex encoded by nuclear genes carries out CoQ₁₀ biosynthesis. Mutations in any of these genes are responsible for the primary CoQ₁₀ deficiency, but there are also different conditions that induce secondary CoQ₁₀ deficiency including mitochondrial DNA (mtDNA) depletion and mutations in genes involved in the fatty acid β-oxidation pathway. The diagnosis of CoQ₁₀ deficiencies is determined by the decrease of its content in skeletal muscle and/or dermal skin fibroblasts. Dietary CoQ₁₀ supplementation is the only available treatment for these deficiencies that require a rapid and distinct diagnosis. Here we review methods for determining CoQ₁₀ content by HPLC separation and identification using alternative approaches including electrochemical detection and mass spectrometry. Also, we review procedures to determine the CoQ₁₀ biosynthesis rate using labeled precursors.

Current concepts in the treatment of hereditary ataxias

Hereditary ataxias (HA) represents an extensive group of clinically and genetically heterogeneous neurodegenerative diseases, characterized by progressive ataxia combined with extra-cerebellar and multi-systemic involvements, including peripheral neuropathy, pyramidal signs, movement disorders, seizures, and cognitive dysfunction. There is no effective treatment for HA, and management remains supportive and symptomatic. In this review, we will focus on the symptomatic treatment of the main autosomal recessive ataxias, autosomal dominant ataxias, X-linked cerebellar ataxias and mitochondrial ataxias. We describe management for different clinical symptoms, mechanism-based approaches, rehabilitation therapy, disease modifying therapy, future clinical trials and perspectives, genetic counseling and preimplantation genetic diagnosis.

Phosphomannomutase deficiency (PMM2-CDG): ataxia and cerebellar assessment

BACKGROUND

Phosphomannomutase deficiency (PMM2-CDG) is the most frequent congenital disorder of glycosylation. The cerebellum is nearly always affected in PMM2-CDG patients, a cerebellar atrophy progression is observed, and cerebellar dysfunction is their main daily functional limitation. Different therapeutic agents are under development, and clinical evaluation of drug candidates will require a standardized score of cerebellar dysfunction. We aim to assess the validity of the International Cooperative Ataxia Rating Scale (ICARS) in children and adolescents with genetically confirmed PMM2-CDG deficiency. We compare ICARS results with the Nijmegen Pediatric CDG Rating Scale (NPCRS), neuroimaging, intelligence quotient (IQ) and molecular data.

METHODS

Our observational study included 13 PMM2-CDG patients and 21 control subjects. Ethical permissions and informed consents were obtained. Three independent child neurologists rated PMM2-CDG patients and control subjects using the ICARS. A single clinician administered the NPCRS. All patients underwent brain MRI, and the relative diameter of the midsagittal vermis was measured. Psychometric evaluations were available in six patients. The Mann-Whitney U test was used to compare ICARS between patients and controls. To evaluate inter-observer agreement in patients' ICARS ratings, intraclass correlation coefficients (ICC) were calculated. ICARS internal consistency was evaluated using Cronbach's alpha. Spearman's rank correlation coefficient test was used to correlate ICARS with NPCRS, midsagittal vermis relative diameter and IQ.

RESULTS

ICARS and ICARS subscores differed between patients and controls (p < 0.001). Interobserver agreement of ICARS was "almost perfect" (ICC = 0.99), with a "good" internal reliability (Cronbach's alpha = 0.72). ICARS was significantly correlated with the total NPCRS score (rs 0.90, p < 0.001). However, there was no agreement regarding categories of severity. Regarding neuroimaging, inverse correlations between ICARS and midsagittal vermis relative diameter (rs -0.85, p = 0.003) and IQ (rs -0.94, p = 0.005) were found. Patients bearing p.E93A, p.C241S or p.R162W mutations presented a milder phenotype.

CONCLUSIONS

ICARS is a reliable instrument for assessment of PMM2-CDG patients, without significant inter-rater variability. Despite our limited sample size, the results show a good correlation between functional cerebellar assessment, IQ and neuroimaging. For the first a correlation between ICARS, neuroimaging and IQ in PMM2-CDG patients has been demonstrated.

Treatable causes of cerebellar ataxia

The cerebellar ataxia syndromes are a heterogeneous group of disorders clinically characterized by the presence of cerebellar dysfunction. Initial assessment of patients with progressive cerebellar ataxia is complex because of an extensive list of potential diagnoses. A detailed history and comprehensive examination are required for an accurate diagnosis and hierarchical diagnostic investigations. Although no cure exists for most of these conditions, a small group of metabolic, hereditary, inflammatory, and immune-mediated etiologies of cerebellar ataxia are amenable to disease-modifying, targeted therapies. Over the past years, disease-specific treatments have emerged. Thus, clinicians must become familiar with these disorders because maximal therapeutic benefit is only possible when done early. In this article, we review disorders in which cerebellar ataxia is a prominent clinical feature requiring targeted treatments along with specific management recommendations.

Mitochondrial ADCK3 employs an atypical protein kinase-like fold to enable coenzyme Q biosynthesis

The ancient UbiB protein kinase-like family is involved in isoprenoid lipid biosynthesis and is implicated in human diseases, but demonstration of UbiB kinase activity has remained elusive for unknown reasons. Here, we quantitatively define UbiB-specific sequence motifs and reveal their positions within the crystal structure of a UbiB protein, ADCK3. We find that multiple UbiB-specific features are poised to inhibit protein kinase activity, including an N-terminal domain that occupies the typical substrate binding pocket and a unique A-rich loop that limits ATP binding by establishing an unusual selectivity for ADP. A single alanine-to-glycine mutation of this loop flips this coenzyme selectivity and enables autophosphorylation but inhibits coenzyme Q biosynthesis in vivo, demonstrating functional relevance for this unique feature. Our work provides mechanistic insight into UbiB enzyme activity and establishes a molecular foundation for further investigation of how UbiB family proteins affect diseases and diverse biological pathways.

Coenzyme Q10 and spinocerebellar ataxias

The aim of this study was to investigate the association between drug exposure and disease severity in SCA types 1, 2, 3 and 6. The Clinical Research Consortium for Spinocerebellar Ataxias (CRC-SCA) enrolled 319 participants with SCA1, 2, 3, and 6 from 12 medical centers in the United States and repeatedly measured clinical severity by the Scale for Assessment and Rating of Ataxia (SARA), the Unified Huntington's Disease Rating Scale part IV (UHDRS-IV), and the 9-item Patient Health Questionnaire during July 2009 to May 2012. We employed generalized estimating equations in regression models to study the longitudinal effects of coenzyme Q10 (CoQ10), statin, and vitamin E on clinical severity of ataxia after adjusting for age, sex, and pathological CAG repeat number. Cross-sectionally, exposure to CoQ10 was associated with lower SARA and higher UHDRS-IV scores in SCA1 and 3. No association was found between statins, vitamin E, and clinical outcome. Longitudinally, CoQ10, statins, and vitamin E did not change the rates of clinical deterioration indexed by SARA and UHDRS-IV scores within 2 years. CoQ10 is associated with better clinical outcome in SCA1 and 3. These drug exposures did not appear to influence clinical progression within 2 years. Further studies are warranted to confirm the association.

Association between coenzyme Q10 and glucose transporter (GLUT1) deficiency

Background

It has been demonstrated that glucose transporter (GLUT1) deficiency in a mouse model causes a diminished cerebral lipid synthesis. This deficient lipid biosynthesis could contribute to secondary CoQ deficiency. We report here, for the first time an association between GLUT1 and coenzyme Q₁₀ deficiency in a pediatric patient.

Case presentation

We report a 15 year-old girl with truncal ataxia, nystagmus, dysarthria and myoclonic epilepsy as the main clinical features. Blood lactate and alanine values were increased, and coenzyme Q₁₀ was deficient both in muscle and fibroblasts. Coenzyme Q₁₀ supplementation was initiated, improving ataxia and nystagmus. Since dysarthria and myoclonic epilepsy persisted, a lumbar puncture was performed at 12 years of age disclosing diminished cerebrospinal glucose concentrations. Diagnosis of GLUT1 deficiency was confirmed by the presence of a de novo heterozygous variant (c.18+2T>G) in the SLC2A1 gene. No mutations were found in coenzyme Q₁₀ biosynthesis related genes. A ketogenic diet was initiated with an excellent clinical outcome. Functional studies in fibroblasts supported the potential pathogenicity of coenzyme Q₁₀ deficiency in GLUT1 mutant cells when compared with controls.

Conclusion

Our results suggest that coenzyme Q₁₀ deficiency might be a new factor in the pathogenesis of G1D, although this deficiency needs to be confirmed in a larger group of G1D patients as well as in animal models. Although ketogenic diet seems to correct the clinical consequences of CoQ deficiency, adjuvant treatment with CoQ could be trialled in this condition if our findings are confirmed in further G1D patients.

Clinical presentations of coenzyme q10 deficiency syndrome

Coenzyme Q10 (CoQ10) deficiency is a clinically and genetically heterogeneous syndrome which has been associated with 5 major clinical phenotypes: (1) encephalomyopathy, (2) severe infantile multisystemic disease, (3) nephropathy, (4) cerebellar ataxia, and (5) isolated myopathy. Of these phenotypes, cerebellar ataxia and syndromic or isolated nephrotic syndrome are the most common. CoQ10 deficiency predominantly presents in childhood. To date, causative mutations have been identified in a small proportion of patients, making it difficult to identify a phenotype-genotype correlation. Identification of CoQ10 deficiency is important because the disease, in particular muscle symptoms and nephropathy, frequently responds to CoQ10 supplementation.

Invertebrate models for coenzyme q10 deficiency

The human syndrome of coenzyme Q (CoQ) deficiency is a heterogeneous mitochondrial disease characterized by a diminution of CoQ content in cells and tissues that affects all the electron transport processes CoQ is responsible for, like the electron transference in mitochondria for respiration and ATP production and the antioxidant capacity that it exerts in membranes and lipoproteins. Supplementation with external CoQ is the main attempt to address these pathologies, but quite variable results have been obtained ranging from little response to a dramatic recovery. Here, we present the importance of modeling human CoQ deficiencies in animal models to understand the genetics and the pathology of this disease, although the election of an organism is crucial and can sometimes be controversial. Bacteria and yeast harboring mutations that lead to CoQ deficiency are unable to grow if they have to respire but develop without any problems on media with fermentable carbon sources. The complete lack of CoQ in mammals causes embryonic lethality, whereas other mutations produce tissue-specific diseases as in humans. However, working with transgenic mammals is time and cost intensive, with no assurance of obtaining results. Caenorhabditis elegans and Drosophila melanogaster have been used for years as organisms to study embryonic development, biogenesis, degenerative pathologies, and aging because of the genetic facilities and the speed of working with these animal models. In this review, we summarize several attempts to model reliable human CoQ deficiencies in invertebrates, focusing on mutant phenotypes pretty similar to those observed in human patients.

Primary coenzyme Q10 (CoQ 10) deficiencies and related nephropathies

Oxidative phosphorylation (OXPHOS) is a metabolic pathway that uses energy released by the oxidation of nutrients to generate adenosine triphosphate (ATP). Coenzyme Q10 (CoQ10), also known as ubiquinone, plays an essential role in the human body not only by generating ATP in the mitochondrial respiratory chain but also by providing protection from reactive oxygen species (ROS) and functioning in the activation of many mitochondrial dehydrogenases and enzymes required in pyrimidine nucleoside biosynthesis. The presentations of primary CoQ10 deficiencies caused by genetic mutations are very heterogeneous. The phenotypes related to energy depletion or ROS production may depend on the content of CoQ10 in the cell, which is determined by the severity of the mutation. Primary CoQ10 deficiency is unique among mitochondrial disorders because early supplementation with CoQ10 can prevent the onset of neurological and renal manifestations. In this review I summarize primary CoQ10 deficiencies caused by various genetic abnormalities, emphasizing its nephropathic form.

Characterization of CoQ₁₀ biosynthesis in fibroblasts of patients with primary and secondary CoQ₁₀ deficiency

Primary coenzyme Q₁₀ (CoQ₁₀) deficiencies are associated with mutations in genes encoding enzymes important for its biosynthesis and patients are responsive to CoQ₁₀ supplementation. Early treatment allows better prognosis of the disease and therefore, early diagnosis is desirable. The complex phenotype and genotype and the frequent secondary CoQ₁₀ deficiencies make it difficult to achieve a definitive diagnosis by direct quantification of CoQ₁₀. We developed a non-radioactive methodology for the quantification of CoQ₁₀ biosynthesis in fibroblasts that allows the identification of primary deficiencies. Fibroblasts were incubated 72 h with 28 μmol/L (2)H₃-mevalonate or 1.65 mmol/L (13)C₆-p-hydroxybenzoate. The newly synthesized (2)H₃- and (13)C₆- labelled CoQ₁₀ were analysed by high performance liquid chromatography-tandem mass spectrometry. The mean and the reference range for (13)C₆-CoQ₁₀ and (2)H₃-CoQ₁₀ biosynthesis were 0.97 (0.83-1.1) and 0.13 (0.09-0.17) nmol/Unit of citrate synthase, respectively. We validated the methodology through the study of one patient with COQ2 mutations and six patients with CoQ₁₀ deficiency secondary to other inborn errors of metabolism. Afterwards we investigated 16 patients' fibroblasts and nine showed decreased CoQ₁₀ biosynthesis. Therefore, the next step is to study the COQ genes in order to reach a definitive diagnosis in these nine patients. In the patients with normal rates the deficiency is probably secondary. In conclusion, we have developed a non-invasive non-radioactive method suitable for the detection of defects in CoQ₁₀ biosynthesis, which offers a good tool for the stratification of patients with these treatable mitochondrial diseases.

Heterozygous Mutations in the ADCK3 Gene in Siblings with Cerebellar Atrophy and Extreme Phenotypic Variability

We describe a highly variable clinical presentation of cerebellar ataxia in two sisters. The younger sister demonstrates early onset rapidly progressive cerebellar ataxia accompanied by motor and nonmotor cerebellar features, as well as cognitive decline and psychiatric problems. Mitochondrial respiratory chain enzyme analysis in muscle showed a decrease in complex I + III. Progressive cerebellar atrophy was demonstrated on serial brain MR imaging. Coenzyme Q10 (CoQ10) supplementation, started at the age of 5 years, led to a significant improvement in motor and cognitive abilities with partial amelioration of the cerebellar signs. Discontinuation of this treatment resulted in worsening of the ataxia, cognitive decline, and severe depression.The older sister, who is 32 years old, has nonprogressive dysarthria and clumsiness from the age of 10 years and MRI reveals cerebellar atrophy.Exome sequencing identified compound heterozygosity for a known (p. Thr584delACC (c.1750_1752delACC)) and a novel (p.P502R) mutation in the ACDK3 gene.

CONCLUSIONS

Patients with primary CoQ10 deficiency due to ADCK3 mutations can demonstrate a wide spectrum of clinical presentations even in the same family. It is difficult to diagnose CoQ10 deficiency based solely on the clinical presentation.Exome sequencing can provide the molecular diagnosis but since it is expensive and not readily available, we recommend a trial of CoQ10 treatment in patients with ataxia and cerebellar atrophy even before confirmation of the molecular diagnosis.

Coenzyme Q10 deficiency in children: frequent type 2C muscle fibers with normal morphology

INTRODUCTION

Neurological disorders with low tissue coenzyme Q10 (CoQ10) levels are important to identify, as they may be treatable.

METHODS

We evaluated retrospectively clinical, laboratory, and muscle histochemistry and oxidative enzyme characteristics in 49 children with suspected mitochondrial disorders. We compared 18 with CoQ10 deficiency in muscle to 31 with normal CoQ10 values.

RESULTS

Muscle from CoQ10-deficient patients averaged 5.5-fold more frequent type 2C muscle fibers than controls (P < 0.0001). A type 2C fiber frequency of ≥ 5% had 89% sensitivity and 84% specificity for CoQ10 deficiency in this cohort. No biopsy showed active myopathy. There were no differences between groups in frequencies of mitochondrial myopathologic, clinical, or laboratory features. Multiple abnormalities in muscle oxidative enzyme activities were more frequent in CoQ10-deficient patients than in controls.

CONCLUSIONS

When a childhood mitochondrial disorder is suspected, an increased frequency of type 2C fibers in morphologically normal muscle suggests CoQ10 deficiency.

Survival transcriptome in the coenzyme Q10 deficiency syndrome is acquired by epigenetic modifications: a modelling study for human coenzyme Q10 deficiencies

OBJECTIVES

Coenzyme Q10 (CoQ10) deficiency syndrome is a rare condition that causes mitochondrial dysfunction and includes a variety of clinical presentations as encephalomyopathy, ataxia and renal failure. First, we sought to set up what all have in common, and then investigate why CoQ10 supplementation reverses the bioenergetics alterations in cultured cells but not all the cellular phenotypes. DESIGN MODELLING STUDY: This work models the transcriptome of human CoQ10 deficiency syndrome in primary fibroblast from patients and study the genetic response to CoQ10 treatment in these cells.

SETTING

Four hospitals and medical centres from Spain, Italy and the USA, and two research laboratories from Spain and the USA.

PARTICIPANTS

Primary cells were collected from patients in the above centres.

MEASUREMENTS

We characterised by microarray analysis the expression profile of fibroblasts from seven CoQ10-deficient patients (three had primary deficiency and four had a secondary form) and aged-matched controls, before and after CoQ10 supplementation. Results were validated by Q-RT-PCR. The profile of DNA (CpG) methylation was evaluated for a subset of gene with displayed altered expression.

RESULTS

CoQ10-deficient fibroblasts (independently from the aetiology) showed a common transcriptomic profile that promotes cell survival by activating cell cycle and growth, cell stress responses and inhibiting cell death and immune responses. Energy production was supported mainly by glycolysis while CoQ10 supplementation restored oxidative phosphorylation. Expression of genes involved in cell death pathways was partially restored by treatment, while genes involved in differentiation, cell cycle and growth were not affected. Stably demethylated genes were unaffected by treatment whereas we observed restored gene expression in either non-methylated genes or those with an unchanged methylation pattern.

CONCLUSIONS

CoQ10 deficiency induces a specific transcriptomic profile that promotes cell survival, which is only partially rescued by CoQ10 supplementation.

Human neuronal coenzyme Q10 deficiency results in global loss of mitochondrial respiratory chain activity, increased mitochondrial oxidative stress and reversal of ATP synthase activity: implications for pathogenesis and treatment

Disorders of coenzyme Q(10) (CoQ(10)) biosynthesis represent the most treatable subgroup of mitochondrial diseases. Neurological involvement is frequently observed in CoQ(10) deficiency, typically presenting as cerebellar ataxia and/or seizures. The aetiology of the neurological presentation of CoQ(10) deficiency has yet to be fully elucidated and therefore in order to investigate these phenomena we have established a neuronal cell model of CoQ(10) deficiency by treatment of neuronal SH-SY5Y cell line with para-aminobenzoic acid (PABA). PABA is a competitive inhibitor of the CoQ(10) biosynthetic pathway enzyme, COQ2. PABA treatment (1 mM) resulted in a 54 % decrease (46 % residual CoQ(10)) decrease in neuronal CoQ(10) status (p < 0.01). Reduction of neuronal CoQ(10) status was accompanied by a progressive decrease in mitochondrial respiratory chain enzyme activities, with a 67.5 % decrease in cellular ATP production at 46 % residual CoQ(10). Mitochondrial oxidative stress increased four-fold at 77 % and 46 % residual CoQ(10). A 40 % increase in mitochondrial membrane potential was detected at 46 % residual CoQ(10) with depolarisation following oligomycin treatment suggesting a reversal of complex V activity. This neuronal cell model provides insights into the effects of CoQ(10) deficiency on neuronal mitochondrial function and oxidative stress, and will be an important tool to evaluate candidate therapies for neurological conditions associated with CoQ(10) deficiency.

Heterogeneity of coenzyme Q10 deficiency: patient study and literature review

Coenzyme Q(10) (CoQ(10)) deficiency has been associated with 5 major clinical phenotypes: encephalomyopathy, severe infantile multisystemic disease, nephropathy, cerebellar ataxia, and isolated myopathy. Primary CoQ(10) deficiency is due to defects in CoQ(10) biosynthesis, while secondary forms are due to other causes. A review of 149 cases, including our cohort of 76 patients, confirms that CoQ(10) deficiency is a clinically and genetically heterogeneous syndrome that mainly begins in childhood and predominantly manifests as cerebellar ataxia. Coenzyme Q(10) measurement in muscle is the gold standard for diagnosis. Identification of CoQ(10) deficiency is important because the condition frequently responds to treatment. Causative mutations have been identified in a small proportion of patients.

Machado-Joseph disease and other rare spinocerebellar ataxias

The spinocerebellar ataxias (SCAs) are a group of neurodegenerative diseases characterised by progressive lack of motor coordination leading to major disability. SCAs show high clinical, genetic, molecular and epidemiological variability. In the last one decade, the intensive scientific research devoted to the SCAs is resulting in clear advances and a better understanding on the genetic and nongenetic factors contributing to their pathogenesis which are facilitating the diagnosis, prognosis and development of new therapies. The scope of this chapter is to provide an updated information on Machado-Joseph disease (MJD), the most frequent SCA subtype worldwide and other rare spinocerebellar ataxias including dentatorubral-pallidoluysian atrophy (DRPLA), the X-linked fragile X tremor and ataxia syndrome (FXTAS) and the nonprogressive episodic forms of inherited ataxias (EAs). Furthermore, the different therapeutic strategies that are currently being investigated to treat the ataxia and non-ataxia symptoms in SCAs are also described.

Primary and secondary CoQ(10) deficiencies in humans

CoQ(10) deficiencies are clinically and genetically heterogeneous. This syndrome has been associated with five major clinical phenotypes: (1) encephalomyopathy, (2) severe infantile multisystemic disease, (3) cerebellar ataxia, (4) isolated myopathy, and (5) nephrotic syndrome. In a few patients, pathogenic mutations have been identified in genes involved in the biosynthesis of CoQ(10) (primary CoQ(10) deficiencies) or in genes not directly related to CoQ(10) biosynthesis (secondary CoQ(10) deficiencies). Respiratory chain defects, ROS production, and apoptosis variably contribute to the pathogenesis of primary CoQ(10) deficiencies.