Early-onset coenzyme Q10 deficiency associated with ataxia and respiratory chain dysfunction due to novel pathogenic COQ8A variants, including a large intragenic deletion

Mitochondrial Dysfunction due to Novel COQ8A Variation with Poor Response to CoQ10 Treatment: A Comprehensive Study and Review of Literatures

COQ8A plays an important role in the biosynthesis of coenzyme Q10 (CoQ10), and variations in COQ8A gene are associated with primary CoQ10 deficiency-4 (COQ10D4), also known as COQ8A-ataxia. The current understanding of the association between the specific variant type, the severity of CoQ10 deficiency, and the degree of oxidative stress in individuals with primary CoQ10 deficiencies remains uncertain. Here we provide a comprehensive analysis of the clinical and genetic characteristics of an 18-year-old patient with COQ8A-ataxia, who exhibited novel compound heterozygous variants (c.1904_1906del and c.637C > T) in the COQ8A gene. These variants reduced the expression levels of COQ8A and mitochondrial proteins in the patient's muscle and skin fibroblast samples, contributed to mitochondrial respiration deficiency, increased ROS production and altered mitochondrial membrane potential. It is worth noting that the optimal treatment for COQ8A-ataxia remains uncertain. Presently, therapy consists of CoQ10 supplementation, however, it did not yield significant improvement in our patient's symptoms. Additionally, we reviewed the response of CoQ10 supplementation and evolution of patients in previous literatures in detail. We found that only half of patients could got notable improvement in ataxia. This research aims to expand the genotype-phenotype spectrum of COQ10D4, address discrepancies in previous reviews regarding the effectiveness of CoQ10 in these disorders, and help to establish a standardized treatment protocol for COQ8A-ataxia.

Adolescence Onset Primary Coenzyme Q10 Deficiency With Rare CoQ8A Gene Mutation: A Case Report and Review of Literature

Background

Primary deficiency of coenzyme Q₁₀ deficiency-4 (CoQ₁₀D4) is a heterogeneous disorder affecting different age groups. The main clinical manifestation consists of cerebellar ataxia, exercise intolerance, and dystonia.

Case report

We provide a case of adolescence-onset ataxia, head tremor, and proximal muscle weakness accompanied by psychiatric features and abnormal serum urea (49.4 mg/dL), lactate (7.5 mmol/L), and CoQ10 level (0.4 µg/mL). Brain-MRI demonstrated cerebellar atrophy, thinning of the corpus callosum, and loss of white matter. Whole exome sequencing showed a homozygous missense mutation (c.911C>T; p.A304V) in CoQ8A gene which is a rare mutation and responsible variant of CoQ₁₀D4. After supplementary treatment with CoQ₁₀ 50 mg/twice a day for 2 months the clinical symptoms improved.

Conclusion

These observations highlight the significance of the early diagnosis of potentially treatable CoQ8A mutation as well as patient education and follow-up. Our findings widen the spectrum of CoQ8A phenotypic features so that clinicians be familiar with the disease not only in severe childhood-onset ataxia but also in adolescence with accompanying psychiatric problems.

EDIR: exome database of interspersed repeats

MOTIVATION

Intragenic exonic deletions are known to contribute to genetic diseases and are often flanked by regions of homology.

RESULTS

In order to get a more clear view of these interspersed repeats encompassing a coding sequence, we have developed EDIR (Exome Database of Interspersed Repeats) which contains the positions of these structures within the human exome. EDIR has been calculated by an inductive strategy, rather than by a brute force approach and can be queried through an R/Bioconductor package or a web interface allowing the per-gene rapid extraction of homology-flanked sequences throughout the exome.

AVAILABILITY AND IMPLEMENTATION

The code used to compile EDIR can be found at https://github.com/lauravongoc/EDIR. The full dataset of EDIR can be queried via an Rshiny application at http://193.70.34.71:3857/edir/. The R package for querying EDIR is called 'EDIRquery' and is available on Bioconductor. The full EDIR dataset can be downloaded from https://osf.io/m3gvx/ or http://193.70.34.71/EDIR.tar.gz.

SUPPLEMENTARY INFORMATION

Supplementary data are available at Bioinformatics online.

Loss of Drosophila Coq8 results in impaired survival, locomotor deficits and photoreceptor degeneration

Coenzyme Q8A encodes the homologue of yeast coq8, an ATPase that is required for the biosynthesis of Coenzyme Q10, an essential component of the electron transport chain. Mutations in COQ8A in humans result in CoQ10 deficiency, the clinical features of which include early-onset cerebellar ataxia, seizures and intellectual disability. The rapid advancement of massively parallel sequencing has resulted in the identification of more than 40 new mutations in COQ8A and functional studies are required to confirm causality and to further research into determining the specific mechanisms through which the mutations result in loss of function. To that end, a Drosophila model of Coq8 deficiency was developed and characterized to determine its appropriateness as a model system to further explore the role of Coq8 in the brain, and for functional characterisation of Coq8 mutations. Pan-neuronal RNAi knockdown of Coq8 was largely lethal, with female escapers displaying severe locomotor deficits. Knockdown of Coq8 in the eye resulted in degeneration of photoreceptors, progressive necrosis and increased generation of reactive oxygen species. Reintroduction of wild-type Coq8 restored normal function, however expression of human wild-type COQ8A exacerbated the eye phenotype, suggesting it was acting as a dominant-negative. This model is therefore informative for investigating the function of Drosophila Coq8, however human COQ8A mutations cannot be assessed as hCOQ8A does not rescue Coq8 deficiency.

Muscle biopsy essential diagnostic advice for pathologists

Background

Muscle biopsies are important diagnostic procedures in neuromuscular practice. Recent advances in genetic analysis have profoundly modified Myopathology diagnosis.

Main body

The main goals of this review are: (1) to describe muscle biopsy techniques for non specialists; (2) to provide practical information for the team involved in the diagnosis of muscle diseases; (3) to report fundamental rules for muscle biopsy site choice and adequacy; (4) to highlight the importance of liquid nitrogen in diagnostic workup. Routine techniques include: (1) histochemical stains and reactions; (2) immunohistochemistry and immunofluorescence; (3) electron microscopy; (4) mitochondrial respiratory chain enzymatic studies; and (5) molecular studies. The diagnosis of muscle disease is a challenge, as it should integrate data from different techniques.

Conclusion

Formalin-fixed paraffin embedded muscle samples alone almost always lead to inconclusive or unspecific results. Liquid nitrogen frozen muscle sections are imperative for neuromuscular diagnosis. Muscle biopsy interpretation is possible in the context of detailed clinical, neurophysiological, and serum muscle enzymes data. Muscle imaging studies are strongly recommended in the diagnostic workup. Muscle biopsy is useful for the differential diagnosis of immune mediated myopathies, muscular dystrophies, congenital myopathies, and mitochondrial myopathies. Muscle biopsy may confirm the pathogenicity of new gene variants, guide cost-effective molecular studies, and provide phenotypic diagnosis in doubtful cases. For some patients with mitochondrial myopathies, a definite molecular diagnosis may be achieved only if performed in DNA extracted from muscle tissue due to organ specific mutation load.