Mitochondrial Disease

What mitochondrial disease is

Almost every cell contains hundreds of mitochondria. They produce ATP, the chemical energy that powers the cell, through a process called oxidative phosphorylation. Mitochondria have a small amount of their own DNA (mtDNA), but most of the proteins they need are coded by genes in the cell nucleus.

A fault in either set of genes can disrupt energy production. When energy runs short, high-demand tissues fail first. Because mitochondria are everywhere, symptoms appear in combinations that do not fit one organ, which is one of the strongest clues to the diagnosis.

Heteroplasmy: why symptoms vary so much

A cell can contain a mix of normal and faulty mtDNA, called heteroplasmy. The proportion differs between tissues and between family members. A mother with few faulty copies may have no symptoms, while her child inherits a high proportion and is severely affected. This makes mitochondrial disease unpredictable even within one family.

Symptoms by body system

Main types and syndromes

• Leigh syndrome: usually starts in infancy, with loss of skills, poor feeding, weak muscles and breathing problems. Often severe.
• MELAS: mitochondrial encephalomyopathy, lactic acidosis and stroke-like episodes. Often starts in childhood or young adulthood with migraine, seizures and stroke-like events.
• MERRF: myoclonic epilepsy with ragged red fibers. Muscle jerks, seizures and ataxia.
• Chronic progressive external ophthalmoplegia (CPEO) and Kearns-Sayre syndrome: drooping eyelids and weak eye movements. Kearns-Sayre also involves the retina and heart conduction.
• Leber hereditary optic neuropathy (LHON): sudden, painless loss of central vision, usually in young men.
• Mitochondrial diabetes and deafness (MIDD).
• POLG-related disorders: a range of conditions from childhood liver failure and seizures (Alpers syndrome) to adult ataxia and neuropathy. People with POLG variants must avoid the seizure medicine valproate.

Diagnosis

Diagnosis is often slow because symptoms overlap with many other diseases. A specialist in metabolic or neuromuscular disease usually leads the workup:

1. Clinical assessment of all organs and family history.
2. Blood and urine tests: lactate and pyruvate, amino acids, organic acids, creatine kinase, and newer markers such as GDF-15.
3. Genetic testing: sequencing of mtDNA and nuclear genes, often whole-exome or whole-genome sequencing. This is now the main diagnostic test.
4. Muscle biopsy: if genetic testing is not conclusive. It can show ragged red fibers and measure the activity of the energy-producing enzymes.
5. Organ checks: MRI of the brain, echocardiogram and ECG, hearing and eye tests, and screening for diabetes.

Treatment and care

There is no cure for most forms, but treatment improves quality of life and prevents crises:

• Supplements: coenzyme Q10, riboflavin, L-carnitine and others are often tried. Evidence is limited, except for primary coenzyme Q10 deficiency, which responds well to CoQ10.
• Specific treatments: idebenone for LHON in some countries, and L-arginine or citrulline during and to prevent stroke-like episodes in MELAS (specialist use).
• Organ-specific care: seizure medicines, pacemakers for heart block, insulin for diabetes, hearing aids or cochlear implants, eyelid surgery, feeding tubes.
• Exercise: gentle, regular aerobic and resistance exercise helps many people with myopathy. Physical and occupational therapy maintain function.
• Illness plans: fever, fasting, dehydration and surgery can trigger deterioration. People should have an emergency letter, avoid prolonged fasting, and receive glucose-containing fluids promptly when unwell.
• Medicines to avoid or use carefully: valproate (especially with POLG), and some anesthetics, statins, aminoglycoside antibiotics and other drugs, as advised by the specialist.

Inheritance and family planning

Mitochondrial DNA disease passes only through the mother. Nuclear gene forms follow recessive, dominant or X-linked patterns. Genetic counseling helps families understand risks. Options can include prenatal testing, preimplantation genetic testing, egg donation, and in some countries mitochondrial donation.

Outlook

The outlook ranges widely. Infant-onset forms such as Leigh syndrome can shorten life significantly. Many adult-onset forms progress slowly, and people live for decades with symptoms managed. Regular monitoring of the heart, hormones, hearing and vision helps catch treatable complications early.

Frequently asked questions

What are the first signs of mitochondrial disease?

There is no single first sign. In children, common early signs are poor growth, weak muscles, developmental delay and seizures. In adults, drooping eyelids, exercise intolerance, hearing loss, diabetes or neuropathy may come first. The pattern of several unrelated organs being affected is the main clue.

How is mitochondrial disease diagnosed?

Doctors combine a detailed history and examination with blood and urine tests and, most importantly, genetic testing of mitochondrial and nuclear DNA. A muscle biopsy is used when genetic results are unclear. Brain MRI, heart tests and hearing and eye checks show which organs are involved.

What is the life expectancy of someone with mitochondrial disease?

It depends on the type and age of onset. Severe forms starting in infancy can be life-limiting in early childhood. Many adult-onset forms progress slowly, and people live into older age. Specialist care that manages heart, breathing and metabolic problems improves survival.

Is mitochondrial disease inherited from the mother?

Sometimes. Faults in mitochondrial DNA are passed only from the mother, because sperm do not pass on mitochondria. But many mitochondrial diseases come from nuclear genes, which can be inherited from either parent. Some cases arise from new genetic changes with no family history.

Can exercise help mitochondrial disease?

Yes, in many people. Supervised, gradually increased aerobic and strength exercise can improve muscle energy production and stamina. Overexertion should be avoided, along with exercising while ill or fasting. A physical therapist familiar with the condition can design a safe program.