Mitochondrial Disease

Overview

Mitochondria are tiny structures inside nearly every cell that convert food and oxygen into the energy the body uses to function. Mitochondrial disease is a group of disorders in which these energy factories do not work properly, so cells cannot make enough energy. The organs that demand the most energy, such as the brain, muscles, heart, eyes, ears, and kidneys, are usually affected first and most severely.

Because every cell relies on mitochondria, the disease can affect almost any part of the body and can range from mild to life-threatening. Some forms appear in infancy or childhood, while others develop in adolescence or adulthood. The pattern of symptoms varies greatly from person to person, even within the same family, which can make these conditions difficult to recognize and diagnose. There is currently no cure, but treatment focuses on supporting affected organs, easing symptoms, and helping people maintain energy and quality of life.

Symptoms

Symptoms depend on which organs are affected and can change over time. Because so many systems can be involved, mitochondrial disease often produces an unusual combination of problems.

• Muscle weakness, low muscle tone, exercise intolerance, and easy fatigue
• Neurological problems such as seizures, developmental delay, or stroke-like episodes
• Vision problems, including drooping eyelids and loss of sight
• Hearing loss
• Heart rhythm problems or weakening of the heart muscle
• Digestive problems, poor growth, and difficulty gaining weight in children
• Diabetes and other hormone problems

A sudden change such as a seizure, severe weakness, or stroke-like symptoms (sudden confusion, trouble speaking, or weakness on one side) needs urgent medical attention.

Causes

Mitochondrial disease is caused by faulty genes that affect how mitochondria are built or how they make energy. The genetic background is unusual because mitochondria carry their own small amount of DNA, separate from the DNA in the cell's nucleus.

• Mitochondrial DNA mutations: These are passed down only from the mother, since a child inherits mitochondria from the egg.
• Nuclear DNA mutations: Many mitochondrial proteins are coded by genes in the cell nucleus, and faults there can be inherited from either parent.

In some people the disease appears as a new genetic change with no family history. Because the proportion of affected mitochondria can differ between cells and organs, two people with the same gene change can have very different symptoms.

Risk Factors

• A family history of mitochondrial disease, especially on the mother's side
• A parent or sibling with an unexplained combination of neurological, muscle, and organ problems
• Carrying a known disease-causing gene change
• In some cases, no identifiable risk factor, as the condition arises from a new mutation

Diagnosis

Diagnosis can be challenging and usually involves a combination of tests at a specialized center.

• Blood and urine tests: May show raised levels of certain chemicals such as lactate, suggesting an energy problem.
• Genetic testing: Examines mitochondrial and nuclear DNA to identify the specific gene change.
• Muscle biopsy: A small sample of muscle examined for abnormal mitochondria and tested for energy-producing function.
• MRI of the brain: Detects characteristic changes in some forms of the disease.
• Heart, hearing, and eye assessments: Screen the organs commonly affected.

Treatment

There is no cure, so care is supportive and aimed at protecting affected organs, managing symptoms, and maintaining function. Treatment is best coordinated by a team that may include neurologists, cardiologists, and other specialists.

• Symptom management: Medicines to control seizures, support the heart, manage diabetes, or treat other specific problems.
• Physical and occupational therapy: Help maintain strength, mobility, and daily function.
• Vitamin and supplement "cocktails": Some people are prescribed combinations of vitamins and supplements thought to support energy production, although benefits vary.
• Avoiding triggers: Illness, fasting, dehydration, extreme temperatures, and certain medications can worsen symptoms and are avoided where possible.
• Nutritional support: Careful attention to diet and adequate calories, especially in children.

Regular monitoring of the heart, hearing, vision, and other organs helps catch and treat new problems early.

Prevention

The disease cannot be prevented because it is genetic, but symptoms and crises can often be reduced.

• Genetic counseling for families to understand inheritance and reproductive options
• Avoiding known triggers such as prolonged fasting, dehydration, and extreme physical stress
• Promptly treating infections and other illnesses, which can drain energy reserves
• Keeping vaccinations up to date as advised to reduce illness
• Working with the care team on safe medications, since some drugs can harm mitochondria

When to See a Doctor

See a doctor if you or your child have an unexplained combination of muscle weakness, fatigue, developmental concerns, vision or hearing changes, and problems affecting several organs. Seek emergency care right away for:

• Seizures, especially if new or prolonged
• Stroke-like symptoms such as sudden confusion, trouble speaking, or weakness on one side
• Severe weakness, breathing difficulty, or a rapidly worsening illness

Related Topics

Frequently Asked Questions

References

1. National Institute of Neurological Disorders and Stroke (NINDS). Mitochondrial Myopathies.
2. MedlinePlus, U.S. National Library of Medicine. Mitochondrial diseases.
3. Mayo Clinic. Mitochondrial myopathy.
4. United Mitochondrial Disease Foundation. About Mitochondrial Disease.