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

Novel pathogenic mtDNA variants in Chinese children with neurological mitochondrial disorders

OBJECTIVE

Pathogenic variations in the mitochondrial genome are tightly linked to neurological mitochondrial disorders in children. However, the mutation spectrum of mitochondrial DNA (mtDNA) in the Chinese population remains incomplete. Therefore, the primary objective of our study was to comprehensively characterize pathogenic mtDNA variants in Chinese children with mitochondrial disorders at clinical, molecular, and functional levels.

METHODS

Between February 2019 and September 2023, we analyzed pathogenic mtDNA variants in a cohort of over 600 Chinese children suspected of having mitochondrial disorders. Whole-exome sequencing (WES) and whole-mtDNA sequencing were performed on the cohort.

RESULTS

We identified 54 pathogenic or likely pathogenic mtDNA variants in 227 Chinese children with neurological mitochondrial disorders. Among the eight novel heteroplasmic variants detected in seven patients, in silico analyses suggested likely pathogenic features. Functional analyses using either primary fibroblasts or cybrid cells carrying different mutant loads of mtDNA variants showed impaired mitochondrial respiration, ATP generation, and mitochondrial membrane potential in five of the eight novel variants, including m.4275G>A, m.10407G>A, m.5828G>A, m.3457G>A, and m.13112T>C. The m.8427T>C variant was identified as a rare polymorphism because, despite being located at MT-ATP8, it does not affect both the assembly and activity of mitochondrial complex V in cells carrying homoplasmic m.8427T>C variation. Transcriptome profiling further confirmed the pathogenic contributions of these five variants by altering mitochondrial pathways.

CONCLUSION

In summary, we revisited the mtDNA mutation spectrum in Chinese children with mitochondrial disorders, and identified five novel pathogenic mtDNA variants with functional verification that are related to neurological mitochondrial disorders in children.

Clinical spectrum, treatment and outcomes of the m.10197G>A mutation in MT-ND3: a case report, systematic review and meta-analysis

BACKGROUND

A correlation between various sites or types of mutations in mitochondrial DNA ND3 and the development of a specific mitochondrial disease or phenotype has yet to be fully established.

METHODS

This study reports a rare case of adult-onset Leigh syndrome (LS) and Leber hereditary optic neuropathy and dystonia (LDYT) overlap syndrome caused by the m.10197G>A mutation in ND3. A review of the literature was conducted to investigate the clinical spectrum, treatment and outcome resulting from the m.10197G>A mutation. Phenotypes associated with the m.10197G>A mutation were classified into three categories: LS/LS+ (LS-involved overlap syndrome), Leber hereditary optic neuropathy (LHON)/LHON+ (LHON-involved overlap syndrome) and other mitochondrial encephalopathies or presentations.

RESULTS

A total of 84 participants (78 patients and 6 asymptomatic carriers) with the m.10197G>A mutation retrieved from 33 articles and the patient whose case we reported were included in the review and meta-analysis. Among all the participants, 55.3% (47/85) and 28.2% (24/85) presented with LS/LS+ and LHON/LHON+, respectively. The median age at onset for LS/LS+ was significantly younger than that for LHON/LHON+ [median, (Q1-Q3), 3.0 (0.58-9.5) vs. 13.5 (5.75-41.75), P = 0.001]. A negative linear correlation was observed between mutation load and age of onset in patients who presented with LS/LS+ (R2 = 0.592, P < 0.001), with the age of onset ranging from infancy to adulthood. Patients with an older age at onset [OR (95% CI), 1.46 (1.12-1.91), P = 0.005] or higher mutation loads [OR (95% CI), 1.14 (1.03-1.26), P = 0.011] were more likely to present with LHON/LHON+ than with LS/LS+. A total of 17 patients were documented as having received a combination of mitochondrial cofactor treatments. Compared with patients with LHON/LHON+, patients with LS/LS+ exhibited an exceedingly high probability of a stable or worsen outcome (93.8% vs. 33.3%, P = 0.006).

CONCLUSIONS

LS/LS+ and LHON/LHON+ are the predominant presentations of the m.10197G>A mutation. An older age at onset and greater mutation load increases the probability of an LHON/LHON+ presentation. Patients presenting with LS/LS+ have an exceedingly high possibility of an unfavorable outcome. The identification of factors and outcomes associated with phenotypes in patients with the m.10197G>A mutation facilitates the provision of improved prognostic counseling for patients and their family members who are carriers of this mutation.

Mitochondrial diseases: from molecular mechanisms to therapeutic advances

Mitochondria are essential for cellular function and viability, serving as central hubs of metabolism and signaling. They possess various metabolic and quality control mechanisms crucial for maintaining normal cellular activities. Mitochondrial genetic disorders can arise from a wide range of mutations in either mitochondrial or nuclear DNA, which encode mitochondrial proteins or other contents. These genetic defects can lead to a breakdown of mitochondrial function and metabolism, such as the collapse of oxidative phosphorylation, one of the mitochondria's most critical functions. Mitochondrial diseases, a common group of genetic disorders, are characterized by significant phenotypic and genetic heterogeneity. Clinical symptoms can manifest in various systems and organs throughout the body, with differing degrees and forms of severity. The complexity of the relationship between mitochondria and mitochondrial diseases results in an inadequate understanding of the genotype-phenotype correlation of these diseases, historically making diagnosis and treatment challenging and often leading to unsatisfactory clinical outcomes. However, recent advancements in research and technology have significantly improved our understanding and management of these conditions. Clinical translations of mitochondria-related therapies are actively progressing. This review focuses on the physiological mechanisms of mitochondria, the pathogenesis of mitochondrial diseases, and potential diagnostic and therapeutic applications. Additionally, this review discusses future perspectives on mitochondrial genetic diseases.

The genetic landscape of mitochondrial diseases in the next-generation sequencing era: a Portuguese cohort study

Introduction: Rare disorders that are genetically and clinically heterogeneous, such as mitochondrial diseases (MDs), have a challenging diagnosis. Nuclear genes codify most proteins involved in mitochondrial biogenesis, despite all mitochondria having their own DNA. The development of next-generation sequencing (NGS) technologies has revolutionized the understanding of many genes involved in the pathogenesis of MDs. In this new genetic era, using the NGS approach, we aimed to identify the genetic etiology for a suspected MD in a cohort of 450 Portuguese patients. Methods: We examined 450 patients using a combined NGS strategy, starting with the analysis of a targeted mitochondrial panel of 213 nuclear genes, and then proceeding to analyze the whole mitochondrial DNA. Results and Discussion: In this study, we identified disease-related variants in 134 (30%) analyzed patients, 88 with nuclear DNA (nDNA) and 46 with mitochondrial DNA (mtDNA) variants, most of them being pediatric patients (66%), of which 77% were identified in nDNA and 23% in mtDNA. The molecular analysis of this cohort revealed 72 already described pathogenic and 20 novel, probably pathogenic, variants, as well as 62 variants of unknown significance. For this cohort of patients with suspected MDs, the use of a customized gene panel provided a molecular diagnosis in a timely and cost-effective manner. Patients who cannot be diagnosed after this initial approach will be further selected for whole-exome sequencing. Conclusion: As a national laboratory for the study and research of MDs, we demonstrated the power of NGS to achieve a molecular etiology, expanding the mutational spectrum and proposing accurate genetic counseling in this group of heterogeneous diseases without therapeutic options.

Clinical Approaches for Mitochondrial Diseases

Mitochondria are subcontractors dedicated to energy production within cells. In human mitochondria, almost all mitochondrial proteins originate from the nucleus, except for 13 subunit proteins that make up the crucial system required to perform 'oxidative phosphorylation (OX PHOS)', which are expressed by the mitochondria's self-contained DNA. Mitochondrial DNA (mtDNA) also encodes 2 rRNA and 22 tRNA species. Mitochondrial DNA replicates almost autonomously, independent of the nucleus, and its heredity follows a non-Mendelian pattern, exclusively passing from mother to children. Numerous studies have identified mtDNA mutation-related genetic diseases. The consequences of various types of mtDNA mutations, including insertions, deletions, and single base-pair mutations, are studied to reveal their relationship to mitochondrial diseases. Most mitochondrial diseases exhibit fatal symptoms, leading to ongoing therapeutic research with diverse approaches such as stimulating the defective OXPHOS system, mitochondrial replacement, and allotropic expression of defective enzymes. This review provides detailed information on two topics: (1) mitochondrial diseases caused by mtDNA mutations, and (2) the mechanisms of current treatments for mitochondrial diseases and clinical trials.

Population-Based Clinical Studies Using Routinely Collected Data in Hong Kong, China: A Systematic Review of Trends and Established Local Practices

Background: Routinely collected health data are increasingly used in clinical research. No study has systematically reviewed the temporal trends in the number of publications and analyzed different aspects of local research practices and their variations in Hong Kong, China, with a specific focus on research ethics governance and approval.

Methods: PubMed was systematically searched from its inception to March 28, 2023, for studies using routinely collected healthcare data from Hong Kong.

Results: A total of 454 studies were included. Between 2000 and 2009, 32 studies were identified. The number of publications increased from 5 to 120 between 2010 and 2022. Of the investigator-led studies using the Hospital Authority (HA)’s cross-cluster data (n = 393), 327 (83.2%) reported receiving ethics approval from a single cluster/university-based REC, whereas 50 studies (12.7%) did not report approval from a REC. For use of the HA Data Collaboration Lab, approval by a single hospital-based or University-based REC is accepted. Repeated submission of identical ethics applications to different RECs is estimated to cost HK$4.2 million yearly.

Conclusions: Most studies reported gaining approval from a single cluster REC before retrieval of cross-cluster HA data. Substantial cost savings would result if repeated review of identical ethics applications were not required.