Leber's hereditary optic neuropathy
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| ICD-10 | H47.2 |
|---|---|
| ICD-9 | 377.16 |
| OMIM | 535000 |
Leber’s hereditary optic neuropathy (LHON) or Leber optic atrophy is a mitochondrially inherited (mother to all offspring) degeneration of retinal ganglion cells (RGCs) and their axons that leads to an acute or subacute loss of central vision; this affects predominantly young adult males. However, LHON is only transmitted through the mother as it is primarily due to mutations in the mitochondrial (not nuclear) genome and only the egg contributes mitochondria to the embryo. LHON is usually due to one of three pathogenic mitochondrial DNA (mtDNA) point mutations. These mutations affect nucleotide positions 11778, 3460 and 14484, respectively in the ND4, ND1 and ND6 subunit genes of complex I of the oxidative phosphorylation chain in mitochondria. Men cannot pass on the disease to their offspring.
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[edit] Signs & symptoms
Clinically, there is an acute onset of visual loss, first in one eye, and then a few weeks later in the other. This eventually evolves to very severe optic atrophy and permanent decrease of visual acuity. In the acute stage lasting a few weeks, the affected eye demonstrates an edematous appearance of the nerve fiber layer especially in the arcuate bundles and enlarged or telangectatic and tortuous peripapillary vessels (microangiopathy). These main features are seen on fundus examination, just before or subsequent to the onset of visual loss. Examination reveals decreased visual acuity, loss of color vision and a cecocentral scotoma on visual field examination.
[edit] Genetics
Leber hereditary optic neuropathy is a condition related to changes in mitochondrial DNA. Mutations in the MT-ND1, MT-ND4, MT-ND4L, and MT-ND6 genes cause Leber hereditary optic neuropathy.
The genes associated with Leber hereditary optic neuropathy are contained in mitochondrial DNA. Mitochondria are structures within cells that convert the energy from food into a form that cells can use. Although most DNA is packaged in chromosomes within the nucleus, mitochondria also have a small amount of their own DNA (known as mitochondrial DNA or mtDNA).
The genes related to Leber hereditary optic neuropathy each provide instructions for making a protein involved in normal mitochondrial function. These proteins are part of a large enzyme complex in mitochondria that helps convert oxygen and simple sugars to energy. Mutations in any of the genes disrupt this process. It remains unclear how these genetic changes cause the death of cells in the optic nerve and lead to the specific features of Leber hereditary optic neuropathy.
A significant percentage of people with a mutation that causes Leber hereditary optic neuropathy do not develop any features of the disorder. Specifically, more than 50 percent of males with a mutation and more than 85 percent of females with a mutation never experience vision loss or related medical problems. Additional factors may determine whether a person develops the signs and symptoms of this disorder. Environmental factors such as smoking and alcohol use may be involved, although studies of these factors have produced conflicting results. Researchers are also investigating whether changes in additional genes, particularly genes on the X chromosome, contribute to the development of signs and symptoms.
[edit] Diagnosis & management
The diagnosis is extremely difficult and usually requires a neuro-ophthalmological evaluation and/or blood testing for DNA assessment (that is available only in a few laboratories). Hence the incidence is probably much greater than appreciated. The prognosis is almost always that of continued very severe visual loss. There is no accepted treatment for this disease.
Leber’s hereditary optic neuropathy is sometimes confused with Leber's congenital amaurosis, which is a different disease also first described by Theodore Leber in the 19th century.
[edit] Epidemiology
- LHON 1 has an unusually high prevalence in Western Quebec, Canada, where it is referred to as Frenchman disease
[edit] See also
[edit] References
- National Library of Medicine. Leber's hereditary optic neuropathy
- Carelli V, Ross-Cisneros F, Sadun A: "Mitochondrial dysfunction as a cause of optic neuropathies." Prog Retinal & Eye Research. 23:53-89, 2004. PMID 14766317
