What are mitochondria?
Mitochondria are the “energy factory” of our body. Several thousand mitochondria are in nearly every cell in the body. Their job is to process oxygen and convert substances from the foods we eat into energy. Mitochondria produce 90% of the energy our body needs to function.
What are mitochondrial diseases?
Mitochondrial diseases are chronic (long-term), genetic, often inherited disorders that occur when mitochondria fail to produce enough energy for the body to function properly. (Inherited means the disorder was passed on from parents to children.) Mitochondrial diseases can be present at birth, but can also occur at any age.
Mitochondrial diseases can affect almost any part of the body, including the cells of the brain, nerves, muscles, kidneys, heart, liver, eyes, ears or pancreas.
Mitochondrial dysfunction occurs when the mitochondria don't work as well as they should due to another disease or condition. Many conditions can lead to secondary mitochondrial dysfunction and affect other diseases, including:
Individuals with secondary mitochondrial dysfunction don't have primary genetic mitochondrial disease and don't need to be concerned about the ongoing development or worsening of symptoms.
How common are mitochondrial diseases?
One in 5,000 individuals has a genetic mitochondrial disease. Each year, about 1,000 to 4,000 children in the United States are born with a mitochondrial disease. With the number and type of symptoms and organ systems involved, mitochondrial diseases are often mistaken for other, more common, diseases.
Symptoms and Causes
What causes mitochondrial disease?
In most people, primary mitochondrial disease is a genetic condition that can be inherited (passed from parents to their children) in several ways.
To understand inheritance types, it’s helpful to learn more about genes and DNA. Genes are substances that give us our traits, such as brown eyes or blue eyes. Genes contain DNA, which is the “blueprint” that gives each person their unique makeup.
Under normal circumstances, a child inherits genes in pairs -- one gene from the mother and one from the father. A child with a mitochondrial disease does NOT receive a normal pair of genes from the parents. The gene has mutated – meaning it has become defective (changed). Learning the way a mitochondrial disease has been inherited helps predict the chance of passing on the disease(s) to future children.
Inheritance types are:
- Autosomal recessive inheritance: This child receives one mutated copy of a gene from each parent. There is a 25% chance that each child in the family will inherit a mitochondrial disease.
- Autosomal dominant inheritance: This child receives one mutated copy of a gene from either parent. There is a 50% chance that each child in the family will inherit a mitochondrial disease.
- Mitochondrial inheritance: In this unique type of inheritance, the mitochondria contain their own DNA. Only mitochondrial disorders caused by mutations in the mitochondrial DNA are exclusively inherited from mothers. If this is the way a mitochondrial disease was inherited, there is a 100% chance that each child in the family will inherit a mitochondrial disease.
- Random mutations: Sometimes genes develop a mutation of their own that is not inherited from a parent.
What are the symptoms of mitochondrial diseases?
Symptoms of mitochondrial diseases depend on which cells of the body are affected. Patients’ symptoms can range from mild to severe, involve one or more organs and can occur at any age. Even patients within the same family who have the same mitochondrial disease can have differences in symptoms, severity and age of onset (start of symptoms).
Symptoms of mitochondrial diseases can include:
- Poor growth.
- Muscle weakness, muscle pain, low muscle tone, exercise intolerance.
- Vision and/or hearing problems.
- Learning disabilities, delays in development.
- Autism spectrum disorder.
- Heart, liver or kidney diseases.
- Gastrointestinal disorders, swallowing difficulties, diarrhea or constipation, unexplained vomiting, cramping, reflux.
- Increased risk of infection.
- Neurological problems, seizures, migraines, strokes.
- Movement disorders.
- Thyroid problems.
- Respiratory (breathing) problems.
- Lactic acidosis (a buildup of lactate).
Diagnosis and Tests
How are mitochondrial diseases diagnosed?
Because mitochondrial diseases affect so many different organs and tissues of the body, and patients have so many different symptoms, mitochondrial diseases can be difficult to diagnose. There is no single laboratory or diagnostic test that can confirm the diagnosis of a mitochondrial disease. This is why referral to a medical facility with physicians who specialize in these diseases is critical to making the diagnosis.
Diagnosis starts with a series of examinations and tests that may include:
- A review of a patient’s family history.
- A complete physical examination.
- A neurological examination.
- A metabolic examination that includes blood and urine tests, and, if needed, a cerebral spinal fluid test (spinal tap).
Other tests, depending on the patient’s symptoms and the areas of the body that are affected, might include:
- Magnetic resonance imaging (MRI) or spectroscopy (MRS) for neurological symptoms.
- Retinal exam or electroretinogram (ERG) for vision symptoms.
- Electrocardiogram (EKG) or echocardiogram for symptoms of heart disease.
- Audiogram or auditory-brainstem evoked responses (ABER) for hearing symptoms.
- Blood test to detect thyroid dysfunction if the patient has thyroid problems.
- Blood test to perform genetic DNA testing.
More advanced testing could include biochemical testing, which looks for changes in body chemicals that are involved in energy making. Biopsies (samples) of skin and muscle tissue may also be performed.
Management and Treatment
How are mitochondrial diseases treated?
There are no cures for mitochondrial diseases, but treatment can help reduce symptoms or slow the decline in health.
Treatment varies from patient to patient and depends on the specific mitochondrial disease diagnosed and its severity. However, there's no way to predict a patient’s response to treatment or predict how the disease will affect that person in the long run. No two people will respond to the same treatment in the same way, even if they have the same disease.
Treatments for mitochondrial disease may include:
- Vitamins and supplements, including Coenzyme Q10; B complex vitamins, especially thiamine (B1) and riboflavin (B2); Alpha lipoic acid; L-carnitine (Carnitor); Creatine; and L-Arginine.
- Exercises, including both endurance exercises and resistance/strength training. These are done to increase muscle size and strength. Endurance exercises include walking, running, swimming, dancing, cycling and others. Resistance/strength training include exercises such as sit-ups, arm curls, knee extensions, weight lifting and others.
- Conserving energy. Don’t try to do too much in a short period of time. Pace yourself.
- Other treatments. These may include speech therapy, physical therapy, respiratory therapy and occupational therapy.
Avoid situations that can make your medical condition worse. These include: exposure to cold and/or heat; starvation; lack of sleep; stressful situations; and use of alcohol, cigarettes and monosodium glutamate (MSG, a flavor enhancer commonly added to Chinese food, canned vegetables, soups, and processed meats).
Outlook / Prognosis
What is the outlook (prognosis) for people who have mitochondrial diseases?
The outlook for people who have mitochondrial diseases depends on how many organ systems and tissues are affected and the severity of disease. Some affected children and adults live near normal lives. Others might experience drastic changes in their health over a very short period of time. Some patients may have flare-ups of their disease, then return to a more stable state for years. Although there's no cure for mitochondrial diseases at the moment, research is ongoing.
Parents with mitochondrial disease(s) who are considering having other children may want to consult a genetic counselor to discuss their concerns.
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