Mitochondrial dysfunction in neurology: biomarkers and clinical implications.

Mitochondrial dysfunction is increasingly recognized as a shared downstream pathogenic mechanism across a wide spectrum of neurological disorders, ranging from primary mitochondrial diseases to conditions including amyotrophic lateral sclerosis, Alzheimer disease, Parkinson disease, multiple sclerosis, hereditary ataxias and idiopathic inflammatory myopathies. This Review examines the role of mitochondrial biomarkers in improving diagnostic accuracy, patient stratification and monitoring of disease progression and therapeutic response. Primary mitochondrial diseases are presented as proof-of-concept models of impaired oxidative phosphorylation, providing a framework for biomarker identification and validation with translational relevance to other neurological diseases. Mitochondrial biomarkers can be broadly categorized into four domains: fluid biomarkers, reflecting metabolic alterations and stress signalling; genetic biomarkers, capturing mitochondrial DNA integrity and dynamics; multi-omics approaches, integrating transcriptomic, proteomic and metabolomic signatures; and imaging biomarkers, enabling in vivo assessment of structural and functional consequences of mitochondrial dysfunction. Across disorders, these biomarkers reveal shared disturbances in bioenergetics, redox homeostasis, mitochondrial genome maintenance and inflammatory signalling. However, clinical implementation remains limited by methodological heterogeneity, biological variability and reduced disease specificity. Integrated, multimodal biomarker strategies, combined with longitudinal validation, will be essential for supporting precision medicine and guiding the development of therapies to target mitochondrial pathways in neurology.