# Symptoms and phases of mitochondrial diseases
Mitochondrial diseases progress very variably, depending on which genes are affected, which tissues suffer most from energy deficiency, and at what stage of life symptoms begin. This tab describes how the disease typically develops and what complaints occur at different stages.
Early manifestation (childhood to young adulthood)
In many people with an inherited mitochondrial disease, the first symptoms appear during childhood or early adolescence, although this can vary greatly. In others, symptoms remain absent for years and only emerge in adulthood.
**Common complaints in this phase:**
- Fatigue and low exercise tolerance (difficulty with sports, play or work of normal intensity)
- Muscle weakness or muscle pain, especially after exertion
- Developmental or learning problems (delayed motor development, difficulty with concentration or memory)
- Digestive complaints: abdominal pain, diarrhea, constipation, swallowing difficulties
- Vision problems or eye movement disorders
- Headaches or migraines
- Hearing problems
- In newborns: feeding problems, poor growth, drowsiness
**Meaning for daily life:**
During this phase, children or young adults may be unable to participate fully with their peers. School can become more difficult, especially with prolonged concentration. Daily normal activities are often still possible, although rest may be needed. Many young people benefit from structure and accommodations (for example, shorter school days, breaks).
**Figures about this phase: **
The severity and progression vary enormously. In some forms (for example certain mtDNA deletions or MELAS) progression can be quite rapid and lead to significant limitations already in the first decade of life. In other forms (such as certain nuclear mutations) the disease can progress much more slowly. There is no single natural history study that applies to all mitochondrial diseases together; the Global Registry and Natural History Study for Mitochondrial Disorders (2026-present) currently collects data to map this better. Individual variation is very large.
Progressive phase (adulthood)
As years pass, symptoms worsen in many patients or new complaints are noticed. The body's cells can increasingly produce less energy, especially under stress.
**Common complaints in this phase:**
- Increasing muscle weakness and muscle wasting
- Worsening fatigue; post-exertional malaise often develops (worsening of symptoms after physical or mental exertion, with recovery time ranging from hours to days)
- Heart complaints: palpitations, cardiac arrhythmias, signs of heart failure
- Neurological symptoms: tremor, coordination disorders (ataxia), poorer hand dexterity
- Non-insulin-dependent diabetes
- Pancreatic disorders
- Kidney function disorders
- Hearing loss that is progressive
- Vision loss due to optic nerve abnormalities
- Cognitive decline, memory problems
- Anxiety disorders or depressive symptoms
- Gastrointestinal complaints and absorption problems
- In more severe forms: brain calcifications, brain tissue damage, strokes without classic causes (MELAS-like episodes)
**Meaning for daily life:**
During this phase, many people become dependent on assistance, home and work accommodations. Regular working hours often become impossible; working from home or part-time work is usually needed. Some require mobility aids. Medical appointments become more frequent. Family members become much more involved in care.
**Figures about this phase: **
For MELAS (mitochondrial encephalomyopathy, lactic acidosis, and stroke-like episodes), median survival after first manifestation is approximately 40-50 years, depending on the study and population (most data from studies of 2010-2020). For MERRF (myoclonic epilepsy with ragged red fibers), median survival is likewise highly variable: several decades, with large individual differences. For Leigh syndrome, which usually presents in infancy, the prognosis is more severe: many children die before age six, although slower-progressing forms have also been described. These figures apply to large groups and say nothing about any one person; in the same genetic form, two patients can have very different courses due to genetic background, environment, and chance.
Severe/advanced phase
In some patients, especially those with early manifestation and severe genetic forms, a point may be reached where vital organs (heart, brain, kidneys) deteriorate significantly.
**Common complaints:**
- Severe muscle paralysis or complete immobility
- Heart failure with fluid accumulation
- Severe brain abnormalities: seizures, dementia, coma
- Respiratory insufficiency (breathing problems); some require mechanical ventilation
- Severe kidney dysfunction, sometimes requiring kidney transplantation
- More severe weight loss and malnutrition despite support
- Sepsis or severe infections due to compromised immunity
- Multi-organ failure
**Meaning for daily life:**
In this phase, patients are usually completely dependent on care, often in a hospital or nursing home. Palliative care and comfort become priority.
**Figures about this phase: **
For the most severe forms (for example, Leigh syndrome with early manifestation), median age at death is often a few years, although this depends greatly on subtype and individual factors. For less severe forms, patients can live for decades in this condition. Precise prognostic figures are difficult because heterogeneity is so great and much data come from clinical experience rather than large prospective studies.
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When to contact your doctor
Many symptoms of mitochondrial diseases can develop gradually. However, there are signals where it makes sense to call your doctor quickly or visit them:
- **New heart rhythm problem, chest pain, shortness of breath:** this may indicate heart involvement and requires rapid evaluation.
- **Sudden vision loss, severe headache with stiffness or confusion, new-onset seizures:** these may indicate acute cerebrovascular complications (especially in MELAS-like forms) and require emergency care.
- **Severe breathing difficulties, chronic cough or infections:** may indicate lung involvement.
- **Severe fatigue, weight loss despite normal eating, or increasing muscle weakness over days/weeks:** may indicate accelerated progression.
- **New or worsening kidney problems, sustained high blood sugar:** requires medical attention.
- **Medication side effects or new complaints after starting a medication:** the treatment may contribute to energy problems and warrants reassessment.
_This information never replaces a doctor's judgment. Always discuss your situation with your own healthcare provider._