Perinatal onset of mitochondrial CoQ10 deficiency due to COQ7 defect with cardiomyopathy and gastrointestinal obstruction

Background

Coenzyme Q10 (CoQ10) is a lipid-soluble molecule with antioxidant properties and a key component in electron transfer during oxidative phosphorylation in mitochondria. CoQ10 deficiency is a rare mitochondrial metabolic disorder typically associated with four main clinical presentations: 1) steroid-resistant nephrotic syndrome (SRNS); 2) encephalopathy, hypertrophic or dilated cardiomyopathy, lactic acidosis, and tubulopathy; 3) neonatal encephalopathy; 4) isolated neurological syndrome. Mutations in COQ series genes are one of the main causes of CoQ10 deficiency.

In clinical practice, early recognition and diagnosis of CoQ10 deficiency are crucial. This is not only because early intervention (such as CoQ10 supplementation) can improve prognosis, but also because these defects often involve multiple organ systems and are complex. The authors of this paper aim to expand the existing clinical and molecular biological understanding of COQ7-related disease spectrum by reporting a case of COQ7 gene defect with novel heterozygous variants.

Paper Source

This paper was written by Ilaria Pettenuzzo, Sara Carli, Ana Sánchez-Cuesta, et al., with the research team affiliated with multiple medical and research institutions including the University of Bologna, Italy, and IRCCS Bologna. The paper was published online in the European Journal of Human Genetics on May 3, 2024.

Research Process

Research Subjects

The research subjects were two affected children from a consanguineous Bangladeshi family. Through whole-exome sequencing (WES) and a series of biochemical and molecular biology experiments, the authors analyzed in detail the clinical manifestations and molecular genetic basis of these two patients.

Clinical Manifestations

The first patient (P1.A) showed abnormalities such as increased fetal nuchal translucency and bilateral choroid plexus cysts during pregnancy, and presented with multi-organ involvement symptoms including hypertrophic cardiomyopathy, incomplete intestinal obstruction, renal insufficiency, and axial hypotonia after birth. The second patient (P1.B) also showed cardiomyopathy and intestinal chloride disease during pregnancy. After birth, P1.B failed to develop well in multiple organ functions and also presented symptoms such as cardiomyopathy, renal insufficiency, and neurodevelopmental delay.

Experimental Methods and Procedures

DNA Extraction and Whole-Exome Sequencing

DNA was extracted from patients’ fibroblasts, and mitochondrial DNA and genomic DNA were analyzed using next-generation sequencing technology. Whole-exome sequencing (WES) was run using the Twist Human Core Exome Kit, and variant calling was performed using GATK tools.

Muscle Biopsy and Ultrastructural Analysis

Muscle biopsies were performed on patients, and mitochondrial structural changes were observed using transmission electron microscopy. Gomori trichrome staining and Oil Red O staining were used to show abnormal lipid accumulation in tissues.

Respiratory Chain Complex Activity Determination

The enzyme activities of respiratory chain complexes I+III and II+III were measured in patients’ muscle homogenates, and it was found that these enzymes completely lost their activity.

mRNA and Protein Expression Analysis

Gene expression and protein levels of COQ7 and COQ9 were analyzed by real-time RT-PCR and Western Blot. The oxygen consumption rate of fibroblasts was measured using a Seahorse XF24 extracellular flux analyzer to assess cellular respiratory function.

Main Results

Gene Mutations

Whole-exome sequencing identified two heterozygous mutations: one is an insertion/deletion variant in exon 6 (c.613_617delgccgginscat), leading to a frameshift mutation; the other is a missense mutation in exon 4 (c.403a>g), resulting in an amino acid substitution in the protein (p.Met135Val). These two mutations were confirmed by family segregation analysis to originate from the parents respectively.

Reduced CoQ10 Levels and Respiratory Chain Activity

Significantly reduced CoQ10 levels were detected in patients’ fibroblasts, and the activity of respiratory chain complexes was completely lost. Western blot and Seahorse analysis results showed increased COQ7 and COQ9 protein levels in patient cells, but mitochondrial function remained significantly reduced.

Research Conclusions

Through detailed clinical characterization and molecular genetic analysis, the research team proved that novel heterozygous mutations in the COQ7 gene are the pathogenic cause of CoQ10 deficiency in patients. The paper emphasizes the importance of multidisciplinary collaboration for early diagnosis and the positive impact of timely high-dose CoQ10 supplementation on patient prognosis.

Research Significance

This study not only expands the disease spectrum related to the COQ7 gene but also for the first time clinically uses fetal ultrasound to detect symptoms of mitochondrial CoQ10 deficiency in advance. The results of this study emphasize the importance of early diagnosis and timely treatment, suggesting that comprehensive genetic and metabolic screening should be performed when mitochondrial disease is suspected. This provides valuable reference for subsequent research and clinical practice.

Conclusion

Through detailed analysis of COQ7 gene variants, this paper not only deepens the understanding of mitochondrial CoQ10 deficiency but also provides new ideas for early identification and treatment of this disease. The research results show that conducting detailed ultrasound examinations and genetic screening during pregnancy can significantly improve early diagnosis and treatment effects, improving patient prognosis. This finding will have a profound impact on future clinical practice and related research.