Scientists have found a protein which is directly linked to age-related macular degeneration, which is the most common cause of blindness in developed countries, a new study published in the journal Nature Communications, has revealed.

The team of international researchers said the protein, called FHR4, is present at higher levels in the blood of patients with age-related macular degeneration (AMD) compared to individuals of a similar age without the disease. FHR4 is one of a group of proteins that regulate the complement system and the genes encoding these proteins are tightly clustered on chromosome 1, the largest human chromosome.

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How to measure blood levels of FHR4

Paul Bishop, professor at the University of Manchester in Britain and one of the researchers, said: "So apart from improving understanding of how AMD is caused, this work provides a way of predicting risk of the disease by simply measuring blood levels of FHR4."

"It also provides a new route to treatment by reducing the blood levels of FHR4 to restore immune system function in the eyes."

According to the researchers, the findings were confirmed in 484 patient and 522 control samples from two independent collections across Europe. The study said that the researchers have also analysed the eyes that were donated for research after life and revealed that the protein was present in the AMD-affected parts of the eye.

The team showed the protein to activate part of the immune system called the complement system. Over-activation is a major causal factor of AMD.

AMD a critical controller

The researchers investigated a set of genetic variants across the human genome and discovered that genetic variants on chromosome 1 determined the levels of FHR4 in the blood. The experts said that the same genetic variants were associated with AMD.

Bishop said: "The combined protein and genetic findings provide compelling evidence that FHR4 is a critical controller of that part of the immune system which affects the eyes. We have shown that genetically determined higher blood FHR4 levels leads to more FHR4 in the eye which in turn increases the risk of the uncontrolled immune system response that drives the disease."