A blood test could help diagnose the world’s most common cause of blindness – years before symptoms develop.
Age-related macular degeneration patients have much higher levels of the FHR-4 protein, scientists have discovered.
The breakthrough could lead to earlier detection when drugs are more likely to be effective and the development of medications that target it.
Ophthalmologists at the University of Manchester say the discovery could lead to a blood test to predict who will get the vision-robbing condition.
Co author Professor Paul Bishop said the ‘compelling’ evidence – taken from a study of 1,000 patients – proves FHR-4 plays a role in the disease.
AMD is the most common cause of blindness, striking 600,000 adults in the UK and less than two million in the US.
Professor Bishop said the work ‘provides a way of predicting risk of the disease by simply measuring blood levels of FHR-4’.
He added: ‘It also provides a new route to treatment by reducing the blood levels of FHR-4 to restore immune system function in the eyes.’
Further analysis of eyes donated for medical research showed the presence of factor H-related protein 4 (FHR-4) in the macula.
In patients with the condition, the macula – the part of the eye responsible for central vision – stops functioning effectively.
It causes central vision to become blurred, resulting in symptoms such as difficulty reading and problems recognising people’s faces.
AMD usually affects both eyes, but the speed of progression can vary between eyes. It is thought to be triggered by aging, smoking and genetics.
Oscar-winning actress Dame Judi Dench, now 85, has been battling the condition since 2012.
She can no longer read her lines and needs the help of family and friends to stop her bumping into things, it has been reported.
The study, published in journal Nature Communications, offers hope of a screening programme that measures the amount of FHR-4 in the blood.
Drugs that destroy it may also provide promising future treatment options, said the researchers.
The protein controls part of the body’s defence called the ‘complement system’ which plays a critical role in inflammation and fighting infection.
Previous studies have linked FHR-4 to AMD, showing genetically inherited faults in key proteins are strong risk factors.
The team, which included colleagues in The Netherlands, mapped the DNA of 1,000 people to identify specific mutations related to increased FHR-4 levels.
Results showed they overlapped with mutations first found to fuel AMD more than two decades earlier.
The combined findings suggest inherited gene faults can lead to more FHR-4 which causes the complement system within the eye to over-reacted, driving disease.
Researchers to compare blood levels of FHR-4 in 484 patients with the disease and 522 without, who acted as controls and were matched by age.