Blindness is prevalent amongst the aging. It affects one in 50 people over 50 and one in five people over 85. The exact cause is unknown, but risk factors include smoking, high blood pressure and having relatives with the condition.
Announced this week, researchers in the United Kingdom have uncovered a probable cause. An enzyme known as DICER1, actually stops functioning, resulting in the handicap.
Professor Jayakrishna Ambati, from the University of Kentucky states:
“This work opens many new doors of research. First, we need to identify various classes of molecules that can either increase DICER1 levels or block Alu RNA so that these can be evaluated in clinical trials. Second, we need to understand more about the biological processes that lead to reduction in DICER1 levels and the precise source of the Alu RNA transcripts.”
This gene encodes a protein possessing an RNA helicase motif containing a DEXH box in its amino terminus and an RNA motif in the carboxy terminus. The encoded protein functions as a ribonuclease and is required by the RNA interference and microRNA (a.k.a. small temporal RNA) pathways to produce the active small RNA component that represses gene expression. Two transcript variants encoding the same protein have been identified for this gene.
The inner layer of the eye is the retina, which contains nerves that communicate sight; behind the retina is the choroid, which contains the blood supply to the macula (the central part of the retina). In the dry (nonexudative) form, cellular debris called drusen accumulate between the retina and the choroid, and the retina can become detached. In the wet (exudative) form, which is more severe, blood vessels grow up from the choroid behind the retina, and the retina can also become detached. It can be treated with laser coagulation, and with medication that stops and sometimes reverses the growth of blood vessels.
As the disease progresses, central vision declines making reading, driving and recognizing people difficult.
It has been discovered that the enzyme DICER1 was less active in the retina of people with the more common “dry form” of the illness and when they turned off the gene which makes the enzyme in mice, then the animal’s retina cells were damaged. It was then discovered that DICER1 is necessary for destroying small pieces of genetic material called Alu RNA.
Without DICER1, the Alu RNA accumulates with toxic consequences leading to the death of the retina.
Professor Ian Grierson, school of clinical sciences at the University of Liverpool, continues:
“This is a great piece of science which provides another jigsaw piece which we need to put together with other findings. It was done in an animal model which is a long way from the patient, the breakthrough is we’ve got another player.”
Professor Mike Cheetham, head of molecular and cellular neuroscience at UCL, finalizes: “It’s a potentially very important breakthrough which gives insight into this dry form of the disease. It could provide new pathways to therapy, but the findings need to be validated by other researchers.”
Various scales have been developed to describe the extent of vision loss and define blindness. Total blindness is the complete lack of form and visual light perception and is clinically recorded as NLP, an abbreviation for “no light perception.” Blindness is frequently used to describe severe visual impairment with residual vision. Those described as having only light perception have no more sight than the ability to tell light from dark and the general direction of a light source.
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Written by Sy Kraft, B.A.