Sample Essay on Leber’s Hereditary Optic Neuropathy
Leber’s hereditary optic neuropathy (LHON) is mitochondrial inherited (transmitted from the mother to the offspring) degeneration of retinal ganglion cells (RGCs) and their axons leading to subacute or acute central vision loss. It is also known as Leber optic atrophy and often affects predominantly young adult males.
LHON can only be transmitted from the mother as it is as a result of mutations in the mitochondrial genome and only the egg is known to contribute mitochondria to the embryo. It occurs as a result of the 3 pathogenic mitochondrial DNA point mutations. The mutations occur at nucleotide positions and they include:
- 11778 G to A
- 3460 G to A
- 14484 T to C
These occur respectively in the ND4, ND1 and ND6 subunit genes of intricate one of the oxidative phosphorylation chain in the mitochondria. It is important to note that the disease cannot be passed on by men, to their offspring.
LHON was first described by Theodar Leber (1840-1917), the German ophthalmologist. In his paper, he described 4 families in which a number of young men suffered sudden vision loss in both eyes either sequentially or simultaneously. Initially, it was assumed the disease was X linked but later it was shown as mitochondrial.
The causative mutation was identified in 1988 for the first time by Wallace who made the discovery of guanine (G) to adenosine (A) mutation at nucleotide position 11778 in 9 families. The mutation converts highly conserved arginine levels to histidine at codon 340 in NADH dehydrogenase subunit 4 of complex one of the mitochondrial respiratory chain. The other 2 mutations that are known to cause the condition were identified in 1991.
The symptoms and signs of Leber’s hereditary optic neuropathy are varied and though this is the case, there are a couple of things that stand out. Clinically, the patient suffers an acute onset of visual loss which starts in one eye and after a couple of weeks or months it progresses to the other eye. Onset is often witnessed in young adulthood but age range variations of onset are reported from the age of 7 to 75.
Age of onset is also higher in females and can range from 19 to 55 years. The mutations of male to female ratio also vary and typically evolve to severe optic atrophy. What is more, those affected also suffer permanent visual acuity decrease. Individuals can also report a history of progressive visual loss in maternal members of a family.
Out of all the cases reported 80% of them are male. The incidence is not increased by lifestyle or age though tobacco and alcohol use is theoretically known to worsen the severity of the disease.
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