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No, not always. Mitochondrial disease can be caused by genetic mutations in either the mitochondrial DNA or the “nuclear” DNA we inherit from our parents. When the mutation is in the mitochondrial DNA, it is passed down from mother to child. Mutations in nuclear DNA may come from either parent or, more commonly, both parents. A third kind of mutation, called a de novo mutation, isn’t inherited it all, but is brand new and arises spontaneously—happening for the first time in the child.
Mitochondrial disease is commonly accepted to be genetic, but it is believed that some people carry mutations that don’t cause mitochondrial disease until they are “triggered” by an environmental factor, such as a toxin or another illness.
Because mitochondria are in every cell in the body, many different organs can be affected when they are damaged or unable to function. Parts of the body that need the most energy, like the heart, brain, muscle and lungs, tend to be affected more, but symptoms vary widely from person to person. A "red flag" for mitochondrial disease is problems in two or more organ systems, rather than any single symptom. Common symptoms and conditions include (but are not limited to) seizures, gastro-intestinal problems, hearing or vision loss, failure to thrive, poor muscle tone, delayed achievement of milestones, stroke, diabetes and heart, kidney or liver problems.
A thorough diagnostic assessment is essential for a number of reasons. First, mitochondrial disease isn’t one disease, but a collection of many different genetic disorders. A thorough assessment to identify the specific disorder will help clinicians select the best treatment.
Secondly, mitochondrial disease has very varied effects from person to person, and many of the symptoms—such as heart failure or general weakness and fatigue—can be caused by a variety of other conditions. For that reason, it’s the overall pattern of symptoms that’s most important in making a diagnosis. Biochemical testing and muscle biopsy can corroborate a diagnosis, but there is no single test that, on its own, can diagnose a mitochondrial disorder. Genetic testing is considered to be the definitive diagnostic test, but since there are many types of genetic tests, they too are guided by each patient’s symptoms.
Sometimes disorders not involving the mitochondria are mistakenly diagnosed as mitochondrial disease. The opposite also is true: Sometimes people who truly have mitochondrial disease are given a different diagnosis.
No. Muscle biopsies are often used to analyze mitochondrial activity, but it is not uncommon for biopsies to miss mitochondrial disease or, conversely, to indicate the presence of mitochondrial disease in people who don’t actually have it. This is because of variation from laboratory to laboratory in how samples are handled and tested and how the results are analyzed. The medical community is developing standards for defining “abnormal” activity that every lab can follow.
Genetic testing, guided by clinical symptoms, is the most definitive way to diagnose mitochondrial disorders.
The prognosis varies from child to child, depending on the severity of the disease and symptoms, so that’s a hard question to answer. In some children, mitochondrial disease progresses quickly and can be very debilitating. In others, it can be stable and well managed for many years. While many children can live full, normal lives if close tabs are kept on their health, others may not survive beyond their teenage years, or may lose their sight or hearing or their ability to walk or talk. Simple illnesses that most people shrug off, like a flu or cold, can be devastating for some children with mitochondrial disease if not treated quickly and aggressively.
Not exactly. While none of the conditions currently have a cure, certain vitamins and supplements seem to improve mitochondrial function and help some patients manage their symptoms. Often given together in “cocktails,” they include coenzyme Q10, creatine and many others that have not to date been well tested. Some mitochondrial disorders can also be treated with compounds that are deficient because of the disease, such as arginine (in MELAS) and folinic acid (in Kearns-Sayre syndrome).
Exercise is one of the few proven methods for improving mitochondrial functioning and can help boost strength and endurance. Simple supportive care (nutrition, hydration and aggressive treatment of infections) is also an important part of managing mitochondrial disease to prevent serious complications from otherwise routine illnesses.
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