Incidence and prevalence of mtDNA-related adult mitochondrial disease in Southwest Finland, 2009-2022: an observational, population-based study

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.

Neurological manifestations in adult patients with the m.3243A>G variant in mitochondrial DNA

ABSTRACT

Background

The m.3243A>G variant in mitochondrial DNA (mtDNA) is the most common cause of the MELAS (Mitochondrial encephalopathy, lactic acidosis and stroke-like episodes) syndrome usually commencing in childhood or adolescence. In adults, the variant presents with versatile and mostly neurological phenotypes, but MELAS may not be common.

Objective

To examine the frequency of phenotypes in adults with m.3243A>G in a population-based cohort and in a meta-analysis of reported case series.

Methods

We clinically examined 51 adult patients with m.3243A>G to determine the frequency of phenotypes and to analyse the contribution of variant heteroplasmy, age, sex and mtDNA haplogroup to the phenotypes. The frequencies of neurological features were also assessed in a meta-analysis on 25 published case series reporting 1314 patients.

Results

Sensorineural hearing impairment (HI), cognitive impairment and myopathy were the most common manifestations, whereas stroke-like episodes were infrequent. Variant heteroplasmy and age were only modest predictors of the phenotypes, although heteroplasmy correlated significantly with disability and Kaplan-Meier analysis showed progression of phenotypes with age. Male sex predicted more severe disability, whereas haplogroup UK was associated with no significant disability. Meta-analysis revealed substantial heterogeneity of phenotype frequencies and preferential inclusion of the MELAS phenotype.

Discussion

In adult patients with m.3243A>G sensorineural HI, cognitive impairment and myopathy are common manifestations with lifetime prevalences approaching unity. Stroke-like episodes are rare. Variant heteroplasmy, age, sex and mtDNA haplogroup contribute to the severity of the disease. Meta-analysis provided a solid estimate of the various neurological symptoms in adults with m.3243A>G.

Primary mitochondrial diseases: The intertwined pathophysiology of bioenergetic dysregulation, oxidative stress and neuroinflammation

OBJECTIVES AND SCOPE

Primary mitochondrial diseases (PMDs) are rare genetic disorders resulting from mutations in genes crucial for effective oxidative phosphorylation (OXPHOS) that can affect mitochondrial function. In this review, we examine the bioenergetic alterations and oxidative stress observed in cellular models of primary mitochondrial diseases (PMDs), shedding light on the intricate complexity between mitochondrial dysfunction and cellular pathology. We explore the diverse cellular models utilized to study PMDs, including patient-derived fibroblasts, induced pluripotent stem cells (iPSCs) and cybrids. Moreover, we also emphasize the connection between oxidative stress and neuroinflammation.

INSIGHTS

The central nervous system (CNS) is particularly vulnerable to mitochondrial dysfunction due to its dependence on aerobic metabolism and the correct functioning of OXPHOS. Similar to other neurodegenerative diseases affecting the CNS, individuals with PMDs exhibit several neuroinflammatory hallmarks alongside neurodegeneration, a pattern also extensively observed in mouse models of mitochondrial diseases. Based on histopathological analysis of postmortem human brain tissue and findings in mouse models of PMDs, we posit that neuroinflammation is not merely a consequence of neurodegeneration but a potential pathogenic mechanism for disease progression that deserves further investigation. This recognition may pave the way for novel therapeutic strategies for this group of devastating diseases that currently lack effective treatments.

SUMMARY

In summary, this review provides a comprehensive overview of bioenergetic alterations and redox imbalance in cellular models of PMDs while underscoring the significance of neuroinflammation as a potential driver in disease progression.