Reference

dictionary Glossary

Medical terminology, explained in plain language. Every major term used across this site, defined in one place.

event Editorial update September 2026
Aminoglycosides
Antibiotics such as gentamicin. Hearing, kidney and genetic risks need individual review. m.3243A>G is not the same as an MT-RNR1 high-risk variant. A class with nephrotoxic and ototoxic potential; MT-RNR1 susceptibility differs from MT-TL1-related disease. 12
Audiometry
Tests that measure hearing at different pitches and volumes. Measurement of auditory thresholds, used to characterise and follow hearing impairment. 23
Cardiomyopathy
Disease of the heart muscle, which can affect its structure or function. Myocardial disease causing structural or functional abnormalities. 2
Cochlear implant (CI)
An implanted hearing device considered for some people when hearing aids do not provide enough benefit. An implanted auditory prosthesis considered after specialist assessment of severe hearing impairment and expected benefit. 23
CoQ10 (Ubiquinone)
A substance involved in mitochondrial energy production, also sold as a supplement. Clinical benefit in m.3243A>G remains uncertain. An electron carrier with limited trial evidence for clinical efficacy in heterogeneous mitochondrial disease. 4
Complex I
One of the protein complexes in the mitochondrial energy-producing system. NADH:ubiquinone oxidoreductase, a respiratory-chain complex contributing to the proton gradient. 56
CSF lactate
Lactate measured in fluid around the brain and spinal cord. It is interpreted with other findings and cannot diagnose or exclude mitochondrial disease alone. Cerebrospinal fluid lactate is a contextual biochemical measure with limited sensitivity and specificity. 7
Electron transport chain (ETC)
A system in mitochondria that helps cells make usable energy. Respiratory-chain electron transfer generates a proton gradient coupled to ATP synthesis. 56
Encephalomyopathy
A condition affecting the brain and muscles. Combined encephalopathic and myopathic involvement. 68
FSGS
Scarring affecting parts of some kidney filtering units. It can occur in mitochondrial disease. Focal segmental glomerulosclerosis, a glomerular lesion reported in mtDNA-related renal disease. 29
GDF-15
A blood marker that may be raised in mitochondrial disease and other conditions. It is not a diagnosis by itself. Growth differentiation factor 15 is a nonspecific stress biomarker; interpretation requires clinical and genetic context. 7
Heteroplasmy
A mixture of mitochondrial DNA copies, some carrying a variant and some not. A reported percentage applies to the sample tested. Coexistence of mtDNA genotypes; measured mutant load is tissue-, age- and assay-dependent and not a deterministic prognosis. 1011
HbA1c
A blood test used to assess longer-term blood sugar levels. Glycated haemoglobin, a measure of longer-term glycaemic exposure interpreted in clinical context. 1213
Histochemistry
Laboratory stains used to examine tissue structure or enzyme activity. Tissue staining to visualise structural and biochemical features, including respiratory-chain abnormalities. 7
L-Arginine
An amino acid studied for stroke-like episodes. Its benefit for treatment or prevention remains unproven. A nitric oxide precursor; uncontrolled reports do not establish acute or prophylactic efficacy in MELAS. 81415
L-Citrulline
An amino acid studied for nitric oxide production. Biochemical changes do not prove that it prevents episodes. A precursor that can augment arginine availability and NO synthesis; clinical efficacy remains unestablished. 81617
Lactic acidosis
Too much lactate together with an acid imbalance in the body. Tiredness alone does not show that it is happening. Hyperlactataemia with metabolic acidosis; clinical and biochemical assessment is required. 28
Linezolid
An antibiotic that may require monitoring for acid buildup and other side effects. It is not banned for every mitochondrial patient. An antibiotic with mitochondrial translation effects; use and lactate surveillance require individual risk–benefit assessment. 1
Maternal inheritance
Passing a DNA change through the egg. Children may inherit different amounts of a mitochondrial variant. Maternal mtDNA transmission with heteroplasmy segregation; paternal transmission is not the usual inheritance pattern. 1819
Metformin
A diabetes medicine requiring individual review because guidance differs and acid-buildup risk matters. A glucose-lowering drug with differing mitochondrial recommendations; assess acidosis susceptibility and renal/hepatic context. 213
MIDD
Maternally inherited diabetes and deafness: a variable pattern of diabetes and hearing loss, sometimes with other organs affected. Mitochondrial diabetes and sensorineural hearing loss phenotype with possible multisystem involvement. 12
Mitochondria
Structures inside cells that help produce usable energy. Organelles supporting oxidative phosphorylation and other metabolic functions. 56
Mitochondrial bottleneck
Changes in the mix of mitochondrial DNA while eggs develop that help explain differences between generations. Germline mtDNA segregation contributing to intergenerational heteroplasmy variation. 1819
Mitochondrial DNA (mtDNA)
DNA inside mitochondria, separate from the DNA in the cell nucleus and usually inherited through the egg. The mitochondrial genome, distinct from nuclear DNA and usually maternally transmitted. 561819
MELAS
A clinical syndrome involving stroke-like episodes and other neurological or body-wide features. Carrying m.3243A>G alone does not mean MELAS. Mitochondrial encephalomyopathy, lactic acidosis and stroke-like episodes; diagnosis requires the clinical syndrome, not genotype alone. 68
MT-TL1
The mitochondrial gene affected by m.3243A>G. It provides instructions for a molecule used in making proteins. The mitochondrial tRNA-Leu(UUR) gene containing m.3243A>G. 56
Myopathy
Muscle disease, which may cause weakness or difficulty with activity. A muscle disorder with variable weakness and exercise intolerance. 220
Neuropathy
A problem affecting nerves outside the brain and spinal cord, sometimes causing numbness, pain or weakness. Peripheral nerve dysfunction with sensory, motor or autonomic manifestations. 2
NGS
Next-generation sequencing: methods that read many DNA pieces to look for genetic changes. High-throughput sequencing used in mitochondrial and nuclear genomic analysis, with assay-specific detection limits. 7
Ophthalmoplegia
Weakness or reduced movement of the eye muscles. Paresis or paralysis of extraocular muscles. 221
PCR
A laboratory method that copies a chosen DNA region so it can be analysed. Polymerase chain reaction amplifies a targeted DNA sequence; quantitative applications depend on the assay. 7
Propofol
An anaesthetic medicine. A brief dose differs from a prolonged infusion, and the plan should be individual. An intravenous anaesthetic requiring procedure-specific risk assessment; prolonged infusion carries distinct metabolic risk. 12
Ptosis
Drooping of an upper eyelid. Upper eyelid droop, which may reflect myopathic or other pathology. 221
Ragged-red fibres
A muscle-biopsy appearance linked to abnormal mitochondrial accumulation. It is not always present. Subsarcolemmal mitochondrial accumulation highlighted by modified Gomori trichrome staining; absence does not exclude disease. 7
Respiratory chain
Another name for the mitochondrial electron transport chain. The mitochondrial respiratory complexes involved in electron transfer and oxidative phosphorylation. 56
Retinopathy
Disease of the light-sensitive tissue at the back of the eye. Retinal disease; macular pattern dystrophy is associated with m.3243A>G. 221
Sensorineural hearing loss
Hearing loss involving the inner ear or hearing nerve pathways. Hearing impairment due to cochlear or neural dysfunction, distinct from conductive loss. 2223
Statins
Cholesterol medicines that may still be used after checking heart and muscle-related risks. Lipid-lowering agents requiring individual cardiovascular benefit and myotoxicity assessment. 1
Stroke-like episode
An episode with new brain-related symptoms that needs urgent assessment. It can resemble other emergencies, including an ordinary stroke. An acute neurological syndrome associated with evolving stroke-like lesions; vascular stroke and other causes still require exclusion. 2824
tRNA
Transfer RNA: a molecule that helps assemble proteins. RNA that carries amino acids for ribosomal protein synthesis; MT-TL1 encodes tRNA-Leu(UUR). 525
Valproate
A seizure medicine with important genetic, liver and pregnancy risks. Do not stop prescribed treatment without specialist advice. An antiseizure medicine with major POLG/hepatic and reproductive safety considerations; supervised review is essential. 262728
WPW syndrome
Wolff–Parkinson–White syndrome: an extra electrical route in the heart that can cause a fast rhythm. An accessory atrioventricular conduction pathway associated with pre-excitation and tachyarrhythmias. 2

References

28 sources

Sources for the information on this page.

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