Mitochondrial Myopathy

What happens in mitochondrial myopathy

Mitochondria contain the respiratory chain, a series of enzyme complexes that use oxygen to make ATP, the cell's energy molecule. Mitochondria have their own small set of DNA (mtDNA), inherited only from the mother, but most mitochondrial proteins are coded by genes in the cell nucleus.

A change in either set of genes can disable the respiratory chain. Muscle cells then switch to less efficient energy production, which makes lactic acid and leaves the muscle short of energy, especially during exercise. Because each cell contains many mitochondria, a person can carry a mix of normal and faulty mtDNA (heteroplasmy). The proportion affects how severe the disease is and which organs are involved, which is why members of the same family can be affected very differently.

Symptoms

Muscle symptoms

• Exercise intolerance: tiring far sooner than expected, with heaviness, aching or burning in the muscles
• Weakness, usually of muscles close to the trunk (shoulders and hips) and the neck
• Muscle pain and cramps after exertion
• Drooping eyelids (ptosis) and limited eye movement (ophthalmoplegia), often slowly progressing over years; double vision is less common than expected
• Weakness of facial and swallowing muscles
• Rarely, muscle breakdown (rhabdomyolysis) after exercise, fasting or infection

Symptoms in other organs

• Heart: cardiomyopathy and heart rhythm problems, including heart block
• Brain: stroke-like episodes, seizures, migraines, learning difficulties, balance problems
• Ears and eyes: hearing loss, retinal changes, optic nerve damage
• Hormones: diabetes, short stature
• Gut: swallowing problems, constipation, poor weight gain
• Nerves: numbness in the feet

Common syndromes

For the wider group of disorders, see mitochondrial disease.

How it is diagnosed

1. History and family tree, including relatives on the mother's side with hearing loss, diabetes, heart disease or neurological problems.
2. Blood tests: lactate and pyruvate (often raised, especially after exercise), creatine kinase (CK, normal or mildly raised), and blood sugar.
3. Genetic testing: often the first-line test now, using blood, urine or saliva for mtDNA and panels or whole-exome or genome sequencing for nuclear genes. Some mtDNA changes are found only in muscle.
4. Muscle biopsy: shows "ragged-red fibers" and fibers lacking the enzyme cytochrome c oxidase, and allows mtDNA and enzyme testing.
5. Other tests: electromyography (EMG), heart ECG and echocardiogram, hearing and eye exams, brain MRI if neurological symptoms are present, and exercise testing.

Other causes of weakness and ptosis, such as myasthenia gravis and muscular dystrophy, are excluded.

Treatment

There is no cure yet. Care aims to maximize energy, prevent complications and treat organ involvement.

• Exercise: supervised aerobic and resistance training, started gently and increased slowly, improves strength and endurance and is safe for most people. Avoid sudden extreme exertion.
• Supplements: coenzyme Q10, L-carnitine, riboflavin and other vitamins are often used. Evidence is limited, so discuss them with your specialist. Specific deficiencies, such as CoQ10 deficiency, respond well. L-arginine or citrulline may be used in MELAS stroke-like episodes.
• Eyelid surgery: a brow suspension or eyelid lift can improve ptosis that blocks vision.
• Heart monitoring: a yearly ECG and regular echocardiograms; a pacemaker if heart block develops.
• Nutrition: regular meals, avoiding long fasts, and extra care during illness.
• Medicine caution: valproate, high-dose or long-term propofol, some antibiotics (such as aminoglycosides in people with certain mtDNA variants) and statins can worsen mitochondrial function. Always tell doctors and anesthetists about your diagnosis.
• Treatments for specific types: a nucleoside therapy has been approved for TK2 deficiency in some countries, and research into gene and other therapies is active.

Outlook

The course ranges from mild, slowly progressive weakness compatible with a normal lifespan, typical of isolated myopathy and many CPEO cases, to severe multi-organ disease in childhood. Heart and breathing involvement are the main determinants of outlook. Regular specialist follow-up catches problems early.

Frequently asked questions

What are the first signs of mitochondrial myopathy?

Often unusual tiredness and muscle aching with ordinary exercise, followed by gradual weakness. In many adults, the first sign is slowly drooping eyelids and reduced eye movement. In children, poor growth, low muscle tone and developmental delay are common early signs.

Is mitochondrial myopathy inherited?

Yes. Changes in mitochondrial DNA are passed from the mother to all her children, though with varying severity. Changes in nuclear genes follow dominant or recessive inheritance. Some cases arise from new mutations. Genetic counseling helps families understand the risk.

Is mitochondrial myopathy fatal?

Not usually when it is limited to the muscles. Many people live a normal or near-normal lifespan with some disability. When the heart, brain or breathing muscles are significantly involved, the condition can shorten life, which is why heart and breathing are monitored regularly.

Can exercise help mitochondrial myopathy?

Yes. Regular, gradually increased aerobic and strength training improves endurance and strength and can increase the number of healthy mitochondria in muscle. Start under the guidance of a specialist or physical therapist and avoid sudden, exhausting exertion.