that cause these disorders on to their children. Mitochondria Cells Cells are the basic building blocks of the body. All tissues and organs are made of billions of different cells. Human cells vary in size, but all are quite small. Even the largest, a fertilized... read more 
are tiny structures inside cells that provide the cells with energy. Mitochondria are present in every cell except red blood cells. Unlike other structures inside cells, mitochondria have some of their own genetic material that is inherited only from the mother. Other genetic material for the mitochondria is in the cell nucleus with the rest of the cell's genetic material, and children with a disorder must inherit an abnormality from each parent.
Mitochondrial disorders cause mitochondria to stop working properly, so that less and less energy is generated within the cells. This may lead to cell injury or even cell death and body systems will not function properly.
Mitochondria supply energy to many organs in the body. Some of these organs, such as the brain, nerves, muscles, and retinas, require more energy than others do. These high-energy organs are particularly susceptible to the problems caused by mitochondrial disorders. Depending on which cells are affected, problems include the following:
Severely reduced muscle tone (hypotonia, or "floppiness")
Weakness of the eye muscles (ophthalmoplegia)
When mitochondria do not function properly, a waste product called lactic acid may build up in the bloodstream (called lactic acidosis). This buildup of lactic acid may help distinguish a mitochondrial disorder from other metabolic diseases. The following are examples of mitochondrial disorders.
Leber hereditary optic neuropathy (LHON)
Leber hereditary optic neuropathy can cause progressive vision loss in both eyes. Some people also have heart problems or muscle symptoms (such as involuntary muscle contractions, muscle weakness, or muscle spasms). The disorder is more common among men, and symptoms often begin when people are in their 20s or 30s.
No treatments are available. However, limiting the consumption of alcohol, which may affect the mitochondria, and not using tobacco products may slow the progression of symptoms. A drug that is injected directly into the space at the back of the eye is currently being studied.
Leigh syndrome
Infants who have Leigh syndrome may have trouble feeding, poor head control, and delayed development. They may also have vomiting, irritability, continuous crying, and seizures that worsen during times of illness. This disorder begins in infants between the ages of 3 months and 2 years. Rarely, it occurs in adolescents and adults. As the disorder progresses, symptoms may also include generalized weakness, lack of muscle tone, and episodes of lactic acidosis, which can lead to breathing and kidney problems.
There are no known treatments for Leigh syndrome. However, a very small number of children have a specific kind of Leigh syndrome that benefits from supplements of thiamin Thiamin Deficiency Thiamin deficiency (causing beriberi and other problems) is most common among people whose diet mainly consists of white rice or highly processed carbohydrates in countries with high rates of... read more (vitamin B1).
Mitochondrial encephalomyopathy, lactic acidosis, and strokelike episodes (MELAS)
Children who have MELAS may have muscle weakness and pain, recurring headaches, hearing loss, loss of appetite, vomiting, and seizures. Most affected people have stroke-like episodes Overview of Stroke A stroke occurs when an artery to the brain becomes blocked or ruptures, resulting in death of an area of brain tissue due to loss of its blood supply (cerebral infarction). Symptoms occur suddenly... read more beginning before age 40. These episodes often cause temporary muscle weakness on one side of the body, altered consciousness, vision abnormalities, seizures, and severe headaches resembling migraines. Repeated stroke-like episodes can progressively damage the brain, leading to vision loss, problems with movement, and dementia. Symptoms of MELAS most often appear in late childhood and adolescence but can begin at any age.
No specific treatment is available for MELAS, but various drugs and treatments are used to manage symptoms.
More Information
The following are some English-language resources that may be useful. Please note that THE MANUAL is not responsible for the content of these resources.
National Organization for Rare Disorders (NORD): This resource provides information to parents and families about rare diseases, including a list of rare diseases, support groups, and clinical trial resources.
Genetic and Rare Diseases Information Center (GARD): This resource provides and easy to understand information about rare or genetic diseases.
