Mitochondria have the important job of changing the nutrients within a cell into energy. Yet, it has only been 10 years since mitochondrial diseases have gained importance, according to Gregory Barsh, M.D., Ph.D., Professor of Pediatrics and Genetics at Stanford University School of Medicine in “Pathophysiology of Disease.” Each cell has several mitochondria and each one of them has several sets of chromosomes. All mitochondrial DNA is passed down through the egg, and never through the sperm.
Leber’s Hereditary Optic Neuropathy
In this mitochondrial disease, a person can lose vision in both eyes. It is painless and can happen suddenly or develop slowly, but the individual is usually blind in two years. In “Pathophysiology of Disease,” Dr. Barsh writes that sometimes people may also have symptoms of heart problems, a lack of coordination in their movements and problems with speech. The disorder usually develops when they are young adults. It is more common in men than in women.
NARP stands for neurogenic weakness, ataxia and retinitis pigmentosa. Neurogenic weakness means the muscles are weak because of abnormalities in the nerves that send signals to the muscles. Ataxia is a lack of coordination in movement, a symptom that people may experience in Leber’s hereditary optic neuropathy. In retinitis pigmentosa, the retina in both eyes slowly degenerates. People may initially have problems with night vision. As the disease develops, they may develop total night blindness as well as daytime vision loss. Parts of their brain will shrink and they may also have brain lesions. A mutation causes NARP. If more than 95 percent of the mitochondrial DNA has mutations, the person develops Leigh’s syndrome, as explained by Karl Skorecki, M.D., Director of Medicine and Research Development at the Ramban Medical Center in “Harrison’s Principles of Internal Medicine.” Leigh’s syndrome is a severe form of NARP.
In “The Merck Manual for Healthcare Professionals,” Chin-To Fong, M.D., Chief of the Division of Pediatric Genetics at the University of Rochester School of Medicine, writes about myoclonic epilepsy with ragged red fibers, or MERRF. People with this mitochondrial disorder may have seizures, ataxia and dementia. They may also have abnormalities in their muscles because the mitochondria are accumulating within them. When a pathologist looks at a muscle biopsy with a special stain, the muscle fibers are described as “ragged-red” fibers. Most people have a mutation in the gene that codes for the amino acid named lysine.
Mitochondrial encephalomyopathy, lactic acidosis and stroke-like episodes is MELAS. This is the most common mitochondrial disease, according to Dr. Skorecki in “Harrison’s Principles of Internal Medicine.” People with this disorder experience several episodes that resemble strokes because of problems primarily located in the back of their brain. Other symptoms may include seizures, reccurring headaches, nausea and vomiting.
In this mitochondrial disorder, people usually have paralysis in some of the muscles in their eyes and problems in their retinas before they are 20 years old. Some may also develop heart problems, ataxia, diabetes mellitus and hearing loss. A milder form of Kearns-Sayre syndrome is referred to as progressive external ophthalmoplegia. People with this mild form may develop ophthalmoplegia, or paralysis in their eye muscles, problems with their muscles, diabetes and hearing loss when they are older than 20 years old. Dr. Skorecki explains that people may develop diabetes in another mitochondrial disease called Pearson syndrome. In addition, they may have lactic acidosis and low levels of all types of blood cells.
- “Harrison’s Principles of Internal Medicine”; Anthony Fauci, M.D., Dennis Kasper, M.D., Dan Longo, M.D. et al.; 2008
- “Pathophysiology of Disease: An Introduction to Clinical Medicine”; Stephen McPhee, M.D., Gary Hammer, M.D., Ph.D.; 2010
- The Merck Manual for Healthcare Professionals: Mitochondrial Oxidative Phosphorylation Disorders