Leber hereditary optic neuropathy (LHON) is a rare genetic disease that causes progressive blindness, typically starting after age 10. Symptoms include blurred vision, problems recognizing people, and worsening color perception. Mutations in four genes responsible for nerve deterioration cause the disease, which is inherited from the mother. Smoking, alcohol, head injury, or stress may be contributing factors.
Leber hereditary optic neuropathy (LHON) is a form of progressive blindness. It is of genetic origin and is extremely rare. Symptoms typically first occur when those affected are over the age of 10.
When a person who has Leber’s hereditary optic neuropathy experiences symptoms of the disease for the first time, they experience blurred vision or blurring of vision. This can occur in both eyes or just one, although both eyes are typically affected eventually. As the disease progresses, the person develops problems seeing well enough to recognize other people by sight, drive a car, or read. Color perception also worsens.
All of these symptoms are caused by the fact that the nerve that transmits visual data to the brain from the eyes is slowly dying. Vision loss usually doesn’t cause any pain, and sometimes vision can improve. Some people who have Leber’s hereditary optic neuropathy, however, also have trouble moving around properly, have irregular heartbeats, or develop a disease similar to multiple sclerosis.
Mutations in some genes are responsible for nerve deterioration. Four major genes are involved: MT-ND1, MT-ND4L, MT-ND4 and MT-ND6. All of these genes are found in particular areas of a human cell.
The parts of the cell that contain genes are called mitochondria. These are small structures that help the cell produce usable energy from food. Most of the genetic information within a cell is held in a different part of the cell, called the nucleus, but mitochondria also have small packages of genes.
Normally, the genes involved in LHON disease perform an essential function for the mitochondria. When one of these genes is mutated, however, the gene does not do its job properly and disease results. As of 2011, it wasn’t known exactly how individual abnormal genes cause problems.
Every human being inherits mitochondria from the mother and none from the father. This is because the egg contains mitochondria, but a sperm does not. When an embryo forms, it has only the mother’s mitochondria and therefore only the mother’s mitochondrial genes.
Inheritance of one of the abnormal genes, therefore, can only come from the mother’s side. On rare occasions, a person may have a spontaneous mutation in their genes that is not inherited. Not everyone who has an abnormal gene will develop Leber hereditary optic neuropathy, although the reasons for this are unknown. Smoking, drinking alcohol, a head injury or stress could be factors in who develops this disease, but these causes had not been proven as of 2011.
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