A molecular mechanism implicated in geographic atrophy, the major cause of untreatable blindness in the industrialized world has been identified by researchers of the University of Kentucky.
Dr. Jayakrishna Ambati and his team also elaborate on a disease-causing role for a large section of the human genome once regarded as non-coding "junk DNA."
Geographic atrophy, a condition causing the death of cells in the retina, occurs in the later stages of the "dry type" of macular degeneration.
The team found that an accumulation of a toxic type of RNA, called Alu RNA, causes retinal cells to die in patients with geographic atrophy. In a healthy eye, a "Dicer" enzyme degrades the Alu RNA particles.
"When the levels of Dicer decline, the control system is short-circuited and too much Alu RNA accumulates. This leads to death of the retina," said Ambati.
The discovery of Alu's toxicity and its control by Dicer should prove of great interest to other researchers in the biological sciences, Ambati said.
His team developed two potential therapies - the first one involves increasing Dicer levels in the retina by "over-expressing" the enzyme and the second one involves blocking Alu RNA using an "anti-sense" drug that binds and degrades this toxic substance.
"These findings provide important new clues on the biological basis of geographic atrophy and may provide avenues for intervention through preventing toxic accumulation of abnormal RNA products," said Dr. Paul Sieving, director of the National Eye Institute.
This work has "widespread implications" for future study, said Dr. Stephen J. Ryan, president of the Doheny Eye Institute and member of the Institute of Medicine.
The study is was published online by the journal Nature on Feb. 6