​A gene mutation in some Chinese is proving to be a double-edged sword.

It gives them added protection against heart attacks, but also significantly increases their risk of going blind, a Singapore-led team of researchers has discovered.

A mutation is a change in the structure of the gene that makes it work slightly or totally different from the norm.

This particular mutation, found almost exclusively in East Asians, raises the level of HDL or good cholesterol, which protects the heart. About 2 per cent to 3 per cent of the Chinese in Singapore have it.

But it also puts them at 70 per cent higher risk of getting age-related macular degeneration (AMD), the top cause of irreversible blindness here, affecting one in 20 people over the age of 40.

Among Chinese with AMD, 5 per cent to 7 per cent had the gene mutation – or more than double that found in the population.

This discovery comes from a huge study led by Singapore clinicians and researchers.

In it, they looked at over a million genetic markers in the DNA of more than 22,000 people in Singapore, China, Japan, South Korea and Hong Kong.

The findings of the year-long study were published last month in Nature Communications, one of the most prestigious research journals in the world.

Associate Professor Cheng Ching-Yu, a clinician scientist at the Singapore Eye Research Institute and the study’s principal investigator, said the findings do not show if the eye condition is due to the mutation or higher levels of HDL these people have.

But an earlier study of 10,000 Asians had shown that those with AMD generally have higher levels of HDL, so there might be a connection. There is no similar link between high HDL levels and AMD in Caucasians.

Associate Professor Gemmy Cheung, a senior consultant at the Singapore National Eye Centre (SNEC), said there is no treatment for early AMD, aside from providing patients with nutrients including vitamins B, C and E.

Treatment for late-stage AMD is monthly or bimonthly injections that cost over $1,000 a jab.

Doctors at the SNEC give more than 4,000 such jabs a year, she said, adding that the number has been going up over the years.

The SNEC said 145,000 people here suffer from AMD, with 14,000 in the late stage.

In the early stage, vision might be a little hazy with blank spots.

In severe cases, a black spot appears in the centre of the vision.

If not treated, it can spread, in a matter of weeks or months, to block out all but peripheral sight.

Associate Professor Tai E Shyong, head of endocrinology at the National University Health System (NUHS) and a member of the team, suspects it is “a subset of those with high HDL” who are prone to AMD, as there are different types of HDL.

His gut feel is that the risk of AMD is linked to the type of HDL caused by the mutation.

If that is true, then other people with a similar type of HDL, even if they lack the mutation, could also be at higher risk of AMD.

At the very least, he said, knowing the link between the mutation and AMD could help drug companies produce more targeted treatment.

Dr Sharon Siddique, president of the Macular Degeneration Society, Singapore, said: “Those of us with AMD can take heart from new discoveries in prevention and cure.

“We are lucky to be living in Singapore, where our eye specialists are in the vanguard of global research.”