Ferroptosis susceptibility in primary coenzyme Q10 deficiency: Cellular insights from patient fibroblasts and clinical course of six individuals.

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.

Steroid-resistant nephrotic syndrome (SRNS) is a genetically heterogeneous kidney disease that is the second most frequent cause of kidney failure in the first 2 decades of life. Despite the identification of mutations in more than 39 genes as causing SRNS, and the localization of its pathogenesis to glomerular podocytes, the disease mechanisms of SRNS remain poorly understood and no universally safe and effective therapy exists to treat patients with this condition. Recently, genetic research has identified a subgroup of SRNS patients whose kidney pathology is caused by primary coenzyme Q10 (CoQ10) deficiency due to recessive mutations in genes that encode proteins in the CoQ10 biosynthesis pathway. Clinical and preclinical studies show that primary CoQ10 deficiency may be responsive to treatment with CoQ10 supplements bypassing the biosynthesis defects. Coenzyme Q10 is an essential component of the mitochondrial respiratory chain, where it transports electrons from complexes I and II to complex III. Studies in yeast and mammalian model systems have recently identified the molecular functions of the individual CoQ10 biosynthesis complex proteins, validated these findings, and provided an impetus for developing therapeutic compounds to replenish CoQ10 levels in the tissues/organs and thus prevent the destruction of tissues due to mitochondrial OXPHOS deficiencies. In this review, we will summarize the clinical findings of the kidney pathophysiology of primary CoQ10 deficiencies and discuss recent advances in the development of therapies to counter CoQ10 deficiency in tissues.

Cases reports: Two females from different families, 34 and 16 years old, who started at puberty with distal weakness in lower limbs and difficulty in walking. The youngest had a history of parental consanguinity. The oldest also developed symptoms of cerebellar ataxia. Both patients had joint hypermobility. After physical exercise, both showed increased serum levels of creatine phosphokinase, but only one of them showed increased lactate. Both electroneuromyography showed motor neuropathy, predominantly in lower limbs, with axonal and demyelinating pathophysiology, with probable superimposed pre-ganglionic involvement. Both genetic tests showed homozygous pathogenic variation in COQ7 gene, described as Chr16:19.067.667, which leads to methionine substitution and impaired protein traduction. Discussion: Primary COQ10 deficiency is a heterogeneous group of mitochondrial disorders caused by defects in proteins involved in COQ10 biosynthesis. It’s inheritance usually is autosomal recessive. Mutations in 10 genes directly involved in coenzyme Q10 synthesis and collectively named “COQ genes” have been identified. Clinical spectrum may overlap encephalomyopathies, ataxia, neuromyopathy, spastic paraplegia and even impairment of another organs. Only four COQ7 deficiency patients have been reported so far. In addition, cases reported here are related with a new variation in COQ7 gene. All reported COQ7 deficiency patients have asian ancestry, which is not the case of patients related here. Some improvement can occur by COQ10 supplementation, which was initiated in both cases. Conclusion: The diagnosis of primary COQ10 deficiency is limited by factors like rarity, heterogeneous phenotypes and unavailability of genetic testes, which favors under or misdiagnosis. Discovery of new cases and mutations can increase our knowledge about this condition, make possible the diagnosis, consequently look for dysfunction of other organs and try a specific treatment.

Oral Coenzyme Q10 supplementation leads to better preservation of kidney function in steroid-resistant nephrotic syndrome due to primary Coenzyme Q10 deficiency

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 syndrome of exercise intolerance, cramps, and myoglobinuria is a common presentation of metabolic myopathies and has been associated with several specific inborn errors of glycogen or lipid metabolism. As disorders in fuel utilization presumably impair muscle energy production, it was more than a little surprising that exercise intolerance and myoglobinuria had not been associated with defects in the mitochondrial respiratory chain, the terminal energy-yielding pathway. Recently, however, specific defects in complex I, complex III, and complex IV have been identified in patients with severe exercise intolerance with or without myoglobinuria. All patients were sporadic cases and all harbored mutations in protein-coding genes of muscle mtDNA, suggesting that these were somatic mutations not affecting the germ-line. Another respiratory chain defect, primary coenzyme Q10 (CoQ10) deficiency, also causes exercise intolerance and recurrent myoglobinuria, usually in conjunction with brain symptoms, such as seizures or cerebellar ataxia. Primary CoQ10 deficiency is probably due to mutations in nuclear gene(s) encoding enzymes involved in CoQ10 biosynthesis.

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.

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.

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.

Primary coenzyme Q10 (CoQ10) deficiency is an autosomal recessive genetic disease caused by mitochondrial dysfunction. Variants in Coenzyme Q8B (COQ8B) can cause primary CoQ10 deficiency. COQ8B-related glomerulopathy is a recently recognized glomerular disease that most often presents as steroid-resistant nephrotic syndrome (SRNS) in childhood. The disease often progresses to kidney failure and the renal histopathology is most commonly focal segmental glomerulosclerosis (FSGS). Four SRNS cases (2 females and 2 males) from 2 unrelated families who were followed clinically for nearly 3 years. Clinical exome testing and analyses were performed by MyGenostics Laboratory in China to evaluate unexplained proteinuria given the strong family history of glomerular disease and histologic evidence of SRNS. Pathogenic variants were identified in COQ8B in the exome studies and confirmed by direct sequencing. Clinical exome sequencing revealed biallelic variants of the COQ8B gene in 2 families. In the Family 1, the oldest of three affected siblings died of renal failure at 11 years of age. Based on the results of genetic testing which identified a homozygous variant of COQ8B, the other two affected siblings with mild proteinuria and normal renal function were treated with CoQ10 oral supplementation at an early stage. Coenzyme Q10 treatment was effective in reducing proteinuria levels in both patients from Family 1 over the first 6 months and the two patients still have low-level proteinuria and normal renal function at nearly three years. In Family 2, clinical exome sequencing revealed a compoundheterozygous variants of COQ8B in a patient with biopsy- proven FSGS. His disease was unresponsive to prior treatment with glucocorticoids and cyclosporine. Oral CoQ10 was initiated based on his genetic diagnosis and was it was effective in reducing proteinuria over the first 5 months months of therapy. However after 1 year, his disease progressed tokidney failure. Kidney transplantation was performed at 5 years of age and his condition has been stable without rejection and no recurrence of disease. COQ8B gene variant-related glomerulopathy often presents as SRNS without obvious extrarenal manifestations. The histopathology is mainly FSGS and follows an autosomal recessive mode of inheritance. Some patients may benefit from early coenzyme Q10 supplementation. For patients whose disease progresses to kidney failure, kidney transplantation can be an effective treatment. For children with unexplained proteinuria and abnormal renal function, genetic testing should be performed early in the course of disease to guide therapy where possible and improve prognosis.

Objective: To explore the clinical and genetic characteristics of infantile nephrotic syndrome caused by COQ2 variants. Methods: The clinical and genetic data of a patient with nephrotic syndrome caused by COQ2 variants diagnosed at pediatric department of Peking University First Hospital from February 2018 to March 2018 were retrospectively analyzed. Related literature retrieved from PubMed, CNKI and Wanfang databases were searched to date (up to July 2018) with "COQ2 gene" or "primary coenzyme Q10 deficiency" and "nephrotic syndrome" or "nephropathy" as key words. Results: A 14-month-old male, presented to local hospital at 11 months of age with edema and severe proteinuria, without hematuria, hypertension or renal dysfunction. He did not have infection or seizure in the course of the disease. He had no response to a more than four-week full-dose prednisone treatment. He had normal birth, mild motor development retardation and moderate language retardation. He was born to non-consanguineous healthy parents. He had two unaffected older sisters and one older sister died of "nephropathy" at one year of age. Genetic testing identified compound heterozygous variants in COQ2 gene: c.518G>A and c.973A>G, both could be predicted by in silico tools to be deleterious in protein function. These variants are not single nucleotide polymorphism and rare in normal populations. Both variants have previously been reported as pathogenic. These missense mutations were inherited from parents in autosomal recessive manner tested by Sanger sequencing. The patient was supplemented with high-dose of coenzyme Q10, at 30 mg/(kg·day) and glucocorticoid was withdrawn. Within three weeks of high dose coenzyme Q10 treatment, the edema disappeared. After seven weeks of high dose coenzyme Q10 treatment, the patient had decreased proteinuria and improved serum albumin levels. The urine protein to creatinine ratio decreased from 22.87 mg/mg to 1.98 mg/mg; Serum albumin increased from 14.2 g/L to 39.9 g/L, with normal kidney function and improved motor development. Primary CoQ10 deficiency is reported to be a rare autosomal recessive mitochondrial disorder with heterogeneous renal, neurologic, and muscular manifestations. To date, COQ2 variants have been reported in 14 children with glomerular involvement. Their age at onset ranged from neonatal period to 10-year-old (8 patients within the first year of life). Steroid resistant nephrotic syndrome (SRNS) is the most common phenotype. Some of these children also had progressing encephalopathy and myopathy, and seizures. Patients with COQ2 variants might show clinical improvement with early high-dose oral CoQ10 supplementation. Literature review revealed two Chinese articles, mainly about adults with neurologic symptoms. SRNS was previously not reported in Chinese pediatric patients. Conclusions: It is necessary to carry out genetic testing for infant with SRNS. The coexistence of some degree of encephalomyopathy, such as development retardation, should raise suspicion of a mitochondrial defect caused by COQ2 variants. Timely diagnostic genetic testing and early high dose of coenzyme Q10 supplement could significantly improve their prognosis.

Nephrotic syndrome can be caused by a subgroup of mitochondrial diseases classified as primary coenzyme Q10 (CoQ10) deficiency. Pathogenic COQ2 variants are a cause of primary CoQ10 deficiency and present with phenotypes ranging from isolated nephrotic syndrome to fatal multisystem disease. We report three pediatric patients with COQ2 variants presenting with nephrotic syndrome. Two of these patients had normal leukocyte CoQ10 levels prior to treatment. Pathologic findings varied from mesangial sclerosis to focal segmental glomerulosclerosis, with all patients having abnormal appearing mitochondria on kidney biopsy. In two of the three patients treated with CoQ10 supplementation, the nephrotic syndrome resolved; and at follow-up, both have normal renal function and stable proteinuria. COQ2 nephropathy should be suspected in patients presenting with nephrotic syndrome, although less common than disease due to mutations in NPHS1, NPHS2, and WT1. The index of suspicion should remain high, and we suggest that providers consider genetic evaluation even in patients with normal leukocyte CoQ10 levels, as levels may be within normal range even with significant clinical disease. Early molecular diagnosis and specific treatment are essential in the management of this severe yet treatable condition.

First demonstration that CoQ10 supplementation is effective for the nephropathy in patients with CoQ10 deficiency. A patient with COQ2 mutations was treated with high dose oral CoQ10 and displayed recovery of the nephrotic syndrome, with normal renal function 5 years after the onset of disease.

Effect of Coenzyme Q10 supplementation on mitochondrial electron transport chain activity and mitochondrial oxidative stress in Coenzyme Q10 deficient human neuronal cells

NG.O.12 - A novel inborn error of the Coenzyme Q10 biosynthesis pathway: cerebellar ataxia and static encephalomyopathy due to COQ5 C-Methyltransferase deficiency