A protein linked to a leading cause of blindness has raised new hopes for the diagnosis and treatment of the debilitating disease.
Scientists say the discovery of the protein, called FHR4, is "a major step forward" in understanding more about age-related macular degeneration (AMD), which affects tens of millions worldwide.
FHR4 was found to be present at higher levels in the blood of AMD patients compared to those of a similar age without the disease.
Professor Paul Bishop, from the University of Manchester in the UK, said their findings provided "a new route to treatment" that would involve "reducing the blood levels of FHR4 to restore immune system function in the eyes".
The researchers analyzed blood samples collected from 484 patients and 522 control test subjects from two independent sources across Europe.
They used a genetic technique, known as a genome-wide association study, to identify specific changes in the genes related to the increased levels of FHR4 in AMD patients.
The team found these genetic changes resulted in the "uncontrolled activation" of a part of the body's immune system known as the complement system.
Researchers believe the over-activation of the complement system to be a key driver of AMD.
Professor Simon Clark, from the University of Manchester, who is a specialist in the regulation of the complement system in health and disease, said: "This study really is a step-change in our understanding of how complement activation drives this major blinding disease.
"Until now, the role played by FHR proteins in disease has only ever been inferred.
"But now we show a direct link and, more excitingly, become a tangible step closer to identifying a group of potential therapeutic targets to treat this debilitating disease."
The study, published in the journal Nature Communications, was carried out by researchers from the universities of Manchester, Cardiff, London, and Nijmegen in the Netherlands, along with the Manchester Foundation NHS Trust.