Definition and genetics
Mitochondrial diseases are a clinically and genetically heterogeneous group of disorders caused by impaired oxidative phosphorylation. Because the respiratory chain is encoded by two genomes — nuclear DNA and the maternally inherited mitochondrial DNA (mtDNA) — inheritance can be autosomal recessive or dominant, X-linked, maternal (mtDNA), or sporadic. mtDNA disorders show heteroplasmy (a mixture of mutant and wild-type genomes) and a threshold effect, which explains their variable, multisystem, and unpredictable expression. The collective prevalence is roughly 1 in 5,000, making mitochondrial disease one of the most common groups of inherited metabolic disorders.
When to suspect
The unifying clue is unexplained involvement of multiple, seemingly unrelated organ systems, particularly those with high energy demand — brain, muscle, heart, eye, ear, kidney, endocrine pancreas, and liver. Suspect mitochondrial disease when a single patient accumulates problems that do not fit one anatomical diagnosis, or when severity is out of proportion to a known trigger.
Clinical features and red flags
- Neurological: developmental regression, refractory epilepsy, stroke-like episodes, ataxia, dystonia, leukoencephalopathy, axonal neuropathy.
- Ophthalmic/aural: progressive external ophthalmoplegia, ptosis, pigmentary retinopathy, optic atrophy, sensorineural hearing loss.
- Cardiac: hypertrophic or dilated cardiomyopathy, conduction block/arrhythmia.
- Other: short stature, diabetes mellitus, renal tubular acidosis (Fanconi), hepatopathy, exercise intolerance, and recurrent/persistent lactic acidosis.
- A maternal-line pedigree of deafness, diabetes, or short stature is a strong pointer.
Diagnosis
Biochemical screening (paired plasma/CSF lactate and pyruvate, plasma amino acids, urine organic acids, acylcarnitine profile, and the plasma GDF-15/FGF-21 biomarkers) supports but never confirms the diagnosis. The clinical likelihood is graded with structured scoring — the modified Walker criteria as adapted by Bernier et al. for children — which combine muscle, CNS, multisystem, metabolic, and imaging features into “definite/probable/possible” probability tiers. In the genomics era, next-generation sequencing (whole-exome or mitochondrial-disease gene panels, plus mtDNA analysis) is the first-line confirmatory test; muscle biopsy with histochemistry and respiratory-chain enzymology is reserved for cases where genetics is non-diagnostic.
See the full criteria: Suspected Mitochondrial Disease.
Management overview
There is no curative therapy; care is supportive and organ-directed. A “mitochondrial cocktail” of vitamin and cofactor supplements (e.g., coenzyme Q10, riboflavin, and related antioxidant/cofactor classes) is widely used with modest evidence. Critical priorities are: anticipating and managing metabolic decompensation during intercurrent illness (avoid prolonged fasting, treat catabolic stress), proactive surveillance and treatment of cardiomyopathy/conduction disease, epilepsy control, hearing and vision support, endocrine screening, and nutrition. Avoid known mitochondrial toxins — valproate (especially in POLG-related disease), aminoglycosides (mtDNA 12S rRNA variants), and caution with propofol and certain anaesthetics. Genetic counselling, including reproductive options for mtDNA disorders, is essential.
References
- Bernier FP, et al. Neurology. 2002.
- Parikh S, et al. Mitochondrial Medicine Society consensus. Genet Med. 2015.
- Witters P, et al. Genet Med. 2018.
Decision support for qualified clinicians only — verify against current primary guidelines and your clinical judgement.