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Individual differences |
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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 are at nucleotide positions 11778 G to A, 3460 G to A and 14484 T to C, 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.
Signs & symptomsEdit
Clinically, there is an acute onset of visual loss, first in one eye, and then a few weeks to months later in the other. Onset is usually young adulthood, but age range at onset from 8-60 is reported. This typically 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.
"LHON Plus" is a name given to rare strains of the disorder with eye disease together with other conditions.  The symptoms of this higher form of the disease include loss of the brain's ability to control the movement of muscles, tremors, and cardiac arrythmia. Many cases of LHON plus have been comparable to Multiple Sclerosis because of the lack of muscular control.
Leber hereditary optic neuropathy is a condition related to changes in mitochondrial DNA. Although most DNA is packaged in chromosomes within the nucleus, mitochondria have a distinct mitochondrial genome composed of mtDNA.
Mutations in the MT-ND1, MT-ND4, MT-ND4L, and MT-ND6 genes cause Leber hereditary optic neuropathy. These genes code for the NADH dehydrogenase protein involved in the normal mitochondrial function of oxidative phosphorylation. Oxidative phosphorylation uses a large multienzyme complex to convert oxygen and simple sugars to energy. Mutations in any of the genes disrupt this process to cause a variety of syndromes depending on the type of mutation and other factors. 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.
The LHON ND4 G11778A mutation dominates as the primary mutation in most of the world with 70% of European cases and 90% of Asian cases. Due to a founder effect, the LHON ND6 T14484C mutation accounts for 86% of LHON cases in Quebec, Canada.
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. The particular mutation type may predict likelihood of penetrance, severity of illness and probability of vision recovery in the affected. 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. The degree of heteroplasmy, the percentage of mitochondria which have mutant alleles, may play a role.  Patterns of mitochondrial alleles called haplogroup may also affect expression of mutations. 
The eye pathology is limited to the retinal ganglion cell layer especially the maculopapillary bundle. Degeneration is evident from the retinal ganglion cell bodies to the axonal pathways leading to the lateral geniculate nucleii. Experimental evidence reveals impaired glutamate transport and increased reactive oxygen species (ROS) causing apoptosis of retinal ganglion cells. Also, experiments suggest that normal non LHON affected retinal ganglion cells produce less of the potent superoxide radical than other normal central nervous system neurons.  Viral vector experiments which augment superoxide dismutase 2 in LHON cybrids  or LHON animal models or use of exogenous glutathione in LHON cybrids have been shown to rescue LHON affected retinal ganglion cells from apoptotic death. These experiments may in part explain the death of LHON affected retinal ganglion cells in preference to other central nervous system neurons which also carry LHON affected mitochondria.
Diagnosis & management Edit
Without a known family history of LHON the diagnosis is 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 greater than appreciated. The prognosis for those affected is almost always that of continued very severe visual loss. Regular corrected visual acuity and perimetry checks are advised for follow up of affected individuals. There is no accepted treatment for this disease. Genetic counselling should be offered.
For those who are carriers of a LHON mutation, preclinical markers may be used to monitor progress. For example fundus photography can monitor nerve fiber layer swelling. Optical coherence tomography can be used for more detailed study of retinal nerve fiber layer thickness. Red green color vision testing may detect losses. Contrast sensitivity may be diminished. There could be an abnormal electroretinogram or visual evoked potentials. Neuron-specific enolase and axonal heavy chain neurofilament blood markers may predict conversion to affected status.
Avoiding optic nerve toxins is generally advised, especially tobacco and alcohol. Certain prescription drugs are known to be a potential risk, so all drugs should be treated with suspicion and checked before use by those at risk. In fact, toxic and nutritional optic neuropathies may have overlaps with LHON in symptoms, mitochondrial mechanisms of disease and management.  Of note, when a patient carrying or suffering from LHON or toxic/nutritional optic neuropathy suffers a hypertensive crisis as a possible complication of the disease process, nitroprusside (trade name: Nipride) should not be used due to increased risk of optic nerve ischemia in response to this anti-hypertensive in particular. 
There are various treatment approaches which have had early trials or are proposed, none yet with convincing evidence of usefulness or safety for treatment or prevention including: Brimonidine;  Minocycline;  Idebenone;  ; Curcumin; glutathione; Near infrared light treatment;  and Viral vector techniques. 
- Dominant optic atrophy
- Ischemic optic neuropathy
- List of eye diseases and disorders
- Optic atrophy
- Toxic and Nutritional Optic Neuropathy
- ↑ Bandelt HJ, Kong QP, Parson W, Salas A (December 2005). More evidence for non-maternal inheritance of mitochondrial DNA?. J. Med. Genet. 42 (12): 957–60.
- ↑ Nikoskelainen EK, Marttila RJ, Huoponen K, et al (August 1995). Leber's "plus": neurological abnormalities in patients with Leber's hereditary optic neuropathy. J. Neurol. Neurosurg. Psychiatr. 59 (2): 160–4.
- ↑ cardiac arrythmia
- ↑ Mayo Clinic: Multiple Sclerosis
- ↑ OMIM 535000
- ↑ Man PY, Griffiths PG, Brown DT, Howell N, Turnbull DM, Chinnery PF (February 2003). The epidemiology of Leber hereditary optic neuropathy in the North East of England. Am. J. Hum. Genet. 72 (2): 333–9.
- ↑ Puomila A, Hämäläinen P, Kivioja S, et al (October 2007). Epidemiology and penetrance of Leber hereditary optic neuropathy in Finland. Eur. J. Hum. Genet. 15 (10): 1079–89.
- ↑ Laberge AM, Jomphe M, Houde L, et al (2005). A "Fille du Roy" introduced the T14484C Leber hereditary optic neuropathy mutation in French Canadians. Am. J. Hum. Genet. 77 (2): 313–7.
- ↑ Hudson G, Carelli V, Horvath R, Zeviani M, Smeets HJ, Chinnery PF (2007). X-Inactivation patterns in females harboring mtDNA mutations that cause Leber hereditary optic neuropathy. Mol. Vis. 13: 2339–43.
- ↑ Hudson G, Keers S, Yu Wai Man P, et al (December 2005). Identification of an X-chromosomal locus and haplotype modulating the phenotype of a mitochondrial DNA disorder. Am. J. Hum. Genet. 77 (6): 1086–91.
- ↑ Chinnery PF, Andrews RM, Turnbull DM, Howell NN (January 2001). <235::AID-AJMG1086>3.0.CO;2-O Leber hereditary optic neuropathy: Does heteroplasmy influence the inheritance and expression of the G11778A mitochondrial DNA mutation?. Am. J. Med. Genet. 98 (3): 235–43.
- ↑ Hudson G, Carelli V, Spruijt L, et al (August 2007). Clinical expression of Leber hereditary optic neuropathy is affected by the mitochondrial DNA-haplogroup background. Am. J. Hum. Genet. 81 (2): 228–33.
- ↑ Hoegger MJ, Lieven CJ, Levin LA (2008). Differential production of superoxide by neuronal mitochondria. BMC Neurosci 9: 4.
- ↑ 14.0 14.1 Qi X, Sun L, Hauswirth WW, Lewin AS, Guy J (February 2007). Use of mitochondrial antioxidant defenses for rescue of cells with a Leber hereditary optic neuropathy-causing mutation. Arch. Ophthalmol. 125 (2): 268–72.
- ↑ 15.0 15.1 Ghelli A, Porcelli AM, Zanna C, Martinuzzi A, Carelli V, Rugolo M (February 2008). Protection against oxidant-induced apoptosis by exogenous glutathione in Leber hereditary optic neuropathy cybrids. Invest. Ophthalmol. Vis. Sci. 49 (2): 671–6.
- ↑ GeneTests LHON search
- ↑ Sadun AA, Salomao SR, Berezovsky A, et al (2006). Subclinical carriers and conversions in Leber hereditary optic neuropathy: a prospective psychophysical study. Trans Am Ophthalmol Soc 104: 51–61.
- ↑ Carelli V, Ross-Cisneros FN, Sadun AA (January 2004). Mitochondrial dysfunction as a cause of optic neuropathies. Prog Retin Eye Res 23 (1): 53–89.
- ↑ Katz, Jason; Patel, Chetan (2006). Parkland Manual of Inpatient Medicine, 903, Dallas, TX: FA Davis.
- ↑ Newman NJ, Biousse V, David R, et al (September 2005). Prophylaxis for second eye involvement in leber hereditary optic neuropathy: an open-labeled, nonrandomized multicenter trial of topical brimonidine purite. Am. J. Ophthalmol. 140 (3): 407–15.
- ↑ Haroon MF, Fatima A, Schöler S, et al (2007). Minocycline, a possible neuroprotective agent in Leber's hereditary optic neuropathy (LHON): Studies of cybrid cells bearing 11778 mutation. Neurobiol Dis 28: 237.
- ↑ Clinical Idebenone trial recruiting at Newcastle University UK http://lhon.ncl.ac.uk
- ↑ Mashima Y, Kigasawa K, Wakakura M, Oguchi Y (September 2000). Do idebenone and vitamin therapy shorten the time to achieve visual recovery in Leber hereditary optic neuropathy?. J Neuroophthalmol 20 (3): 166–70.
- ↑ Clinical Curcurmin trial recruiting at ClinicalTrials.nlm.nih.gov
- ↑ Wisconsin near infrared trial
- ↑ Who Named It doctor/1158
- ↑ Leber T (1869). Über Retinitis pigmentosa und angeborene Amaurose Albrecht von Graefes. Archiv für Ophthalmologie 15 (3): 1–25.
- Yu-Wai-Man P, Chinnery P (2008) Leber Hereditary Optic Neuropathy. GeneReviews
- Kerrison JB, Newman NJ (1997). Clinical spectrum of Leber's hereditary optic neuropathy. Clin. Neurosci. 4 (5): 295–301.
- Carelli V, Ross-Cisneros FN, Sadun AA (January 2004). Mitochondrial dysfunction as a cause of optic neuropathies. Prog Retin Eye Res 23 (1): 53–89.
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