Paeds · genetics-dysmorphology-and-metabolism
Mitochondrial disease
Also known as Mitochondrial disease · Mitochondrial cytopathy · Mitochondrial encephalomyopathy · OXPHOS disorder · Respiratory chain disease · MELAS · Leigh syndrome
A fellowship approach to mitochondrial disease: recognise the energy-failure phenotype across high-demand tissues, hold the dual-genome logic (maternal mtDNA versus Mendelian nDNA) and the heteroplasmy-threshold principle that explains variability, investigate in tiers from lactate to dual-genome sequencing to selective muscle biochemistry, and manage with supportive multidisciplinary care plus the hard pharmacological constraints — above all the absolute avoidance of valproate in POLG-related disease.
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Target exams
Red flags
- A child with unexplained symptoms crossing multiple specialty boundaries — brain, muscle, gut, heart — has mitochondrial disease until proven otherwise
- An infant or young child with status epilepticus, liver dysfunction, and developmental regression has Alpers-Huttenlocher syndrome (POLG) until excluded — and valproate can be fatal
- Persistent or episodic lactic acidosis out of proportion to illness, especially with neurological signs, signals a primary mitochondrial disorder
- A maternal family history of diabetes and deafness in a child presenting with stroke-like episodes is MELAS (m.3243A>G) until tested
- Painless subacute central visual loss in an adolescent male with disc telangiectasia on fundoscopy is Leber hereditary optic neuropathy until the mtDNA result returns
- New ptosis and progressive external ophthalmoplegia in a child with pigmentary retinopathy, ataxia, or heart block is Kearns-Sayre syndrome — the conduction disease can cause sudden death
- Bilateral symmetric basal-ganglia and brain-stem signal change on MRI in a hypotonic, failing-to-thrive infant is Leigh syndrome until biochemically and genetically explained
Life stages
Care settings
Clinical exam formats
Board mappings
- General and Community Paediatrics
- Neurology and Metabolic Medicine
- Neonatal Medicine
- Metabolic Medicine - recognise, investigate and manage mitochondrial disorders
- Neurology - assess the hypotonic infant and the child with neurodegeneration
- Genetics - apply dual-genome inheritance and genetic counselling for mtDNA and nuclear defects
- Metabolic 1-6
- Clinical Applications
- Long Cases
- Short Cases
- 1. Neonates and infants with congenital abnormalities
- 2. Inherited metabolic disorders and neurodegeneration
- 9. Metabolic and genetic conditions
- Foundation of Practice (FOP)
- Theory and Science (TAS)
- Applied Knowledge in Practice (AKP)
- Clinical
- Development
- Communication
- History
- General Pediatrics Content Outline - D21 Metabolic Disorders (3%)
- General Pediatrics Content Outline - D17 Neurology (7%)
- General Pediatrics Content Outline - D19 Genetics (6%)
- Patient Care 4: Clinical Reasoning
- Medical Knowledge 1: Genetic and Metabolic Disorders
- Medical Knowledge 2: Neurologic Disorders
- Systems-Based Practice 1: Patient Safety - medication avoidance
- Medical Expert
- Pediatrics: Metabolic - mitochondrial disorders
- Pediatrics: Neurology - neurodegenerative disease
A two-year-old is admitted with refractory seizures, vomiting, and drowsiness after a febrile illness. The lactate is high, the liver is enlarging, and the development that the parents were proud of a month ago has stalled. Across the ward, a teenager presents with painless loss of central vision, and in clinic a mother and her son both have diabetes and deafness. The fellowship task in mitochondrial disease is not to memorise a single syndrome but to recognise the energy-failure signature — the way a defect in ATP supply produces symptoms that cross conventional specialty boundaries — and to act on the few decisions that genuinely change outcome: confirm the genetic defect, avoid the mitochondrial toxins, and support the failing systems. [2] [7]
Hold ten facts and the topic organises itself: Multi-system, energy-demand tissues fail first (brain, muscle, heart, liver, kidney); Inheritance is dual — mtDNA maternal, nDNA Mendelian; Threshold effect — mutant load must exceed a tissue level to cause disease; OXPHOS (complexes I–V) is the shared final pathway; Co-enzyme Q10, riboflavin, L-carnitine form the 'mito cocktail'; Heteroplasmy — cells carry a mix of normal and mutant genomes; Optic atrophy and deafness are common; Never give valproate in POLG disease; Depletion syndromes (hepatic, encephalomyopathic) from nuclear maintenance genes; Ragged-red fibres on muscle histology; Idebenone is licensed for LHON; Arginine (L-arginine) is given early in MELAS stroke-like episodes. [2] [12]
Overview & Definition
Mitochondrial diseases are a group of genetically determined disorders in which the oxidative phosphorylation system fails to meet cellular energy demand, producing a characteristic pattern of dysfunction in tissues with the highest ATP requirement. They are among the most common inherited metabolic disorders, and they are also among the most protean — a single molecular defect can present in infancy with catastrophic encephalopathy or in adulthood with isolated deafness, and everything in between. The reason for this variability is biological, not arbitrary, and understanding it is the foundation of the fellowship answer. [2] [1]
The unit of function is the respiratory chain: five multi-subunit enzyme complexes (I–V) embedded in the inner mitochondrial membrane that use electrons harvested from food to pump protons, generating the electrochemical gradient that drives ATP synthase. Only thirteen of the roughly ninety subunits of this machinery are encoded by mitochondrial DNA; the remainder, and all of the assembly, maintenance, translation and import factors, are encoded by nuclear genes. A defect in either genome — and in over a thousand nuclear genes by current count — can disable the chain, which is why the clinical and genetic landscape is so large. [2] [3]
Because the phenotype reflects inadequate energy supply, it tracks the tissues that consume the most energy. The central nervous system, skeletal muscle, cardiac muscle, liver, renal tubules, pancreatic beta cells, endocrine glands, retina and cochlea are all high-demand tissues, and mitochondrial disease declares itself across them in combinations that no single-organ diagnosis explains. The bedside clue that unifies these combinations is the energy-failure signature: symptoms that cross specialty boundaries, fluctuate with metabolic stress, and are out of proportion to the apparent trigger. [2] [9]
References13ShowHide
- [1]Gorman GS, Schaefer AM, Ng Y, Gomez N, Blakely EL, Alston CL, Feeney C, Horvath R, Yu-Wai-Man P, Chinnery P, Taylor RW, Turnbull DM, McFarland R. Prevalence of nuclear and mitochondrial DNA mutations related to adult mitochondrial disease. Ann Neurol, 2015.PMID 25652200
- [2]Klopstock T, Priglinger C, Yilmaz A, et al. Mitochondrial Disorders. Dtsch Arztebl Int, 2021.PMID 34158150
- [3]Chin HL, Lai PS, Tay SKH A clinical approach to diagnosis and management of mitochondrial myopathies. Neurotherapeutics, 2024.PMID 38241155
- [4]El-Hattab AW, Adesina AM, Jones J, Scaglia F. MELAS syndrome: Clinical manifestations, pathogenesis, and treatment options. Mol Genet Metab, 2015.PMID 26095523
- [5]Tetsuka S, Ogawa T, Hashimoto R, et al. Clinical features, pathogenesis, and management of stroke-like episodes due to MELAS. Metab Brain Dis, 2021.PMID 34118021
- [6]Rahman S Leigh syndrome. Handb Clin Neurol, 2023.PMID 36813320
- [7]Rahman S, Copeland WC. POLG-related disorders and their neurological manifestations. Nat Rev Neurol, 2019.PMID 30451971
- [8]Lim A, Thomas RH The mitochondrial epilepsies. Eur J Paediatr Neurol, 2020.PMID 31973983
- [9]Hirano M, Pitceathly RDS Progressive external ophthalmoplegia. Handb Clin Neurol, 2023.PMID 36813323
- [10]Karaa A, Goldstein A. The spectrum of clinical presentation, diagnosis, and management of mitochondrial forms of diabetes. Pediatr Diabetes, 2015.PMID 25330715
- [11]Hage R, Vignal-Clermont C. Leber Hereditary Optic Neuropathy: A Review of Treatment and Management. Front Neurol, 2021.PMID 34122299
- [12]Mancuso M, Papadopoulou MT, Ng YS, et al. Management of seizures in patients with primary mitochondrial diseases: Consensus statement from the mitochondrial medicine society. Eur J Neurol, 2024.PMID 38576261
- [13]Wang H, Han Y, Li S, et al. Mitochondrial DNA Depletion Syndrome and Its Associated Cardiac Disease. Front Cardiovasc Med, 2021.PMID 35237671