Sights set on genetics

Tue, Sep 25, 2012, 01:00

IRISH PEOPLE have a genetic predisposition to a condition that is the most common cause of registered blindness in this country, according to new research released this week.

Genetic abnormalities associated with age-related macular degeneration (AMD), which have been identified among white populations elsewhere in the world, have now been shown to be very common among Irish AMD patients too.

An estimated 70,000 people in Ireland have some form of AMD. The biggest risk factor is being over the age of 50; other risks include smoking, being overweight and having high blood pressure, as well as a family history of the condition.

The retina in the eye sits on pigmented cells that look like brown velvet, explains eye surgeon Mark Cahill of the Royal Victoria Eye and Ear Hospital in Dublin. That pigment becomes thinner in everybody with age.

“What we are trying to figure out worldwide is why some people’s pigment gets thinner than others,” says Cahill, who was co-director of the new research with Dr Marian Humphries in the department of genetics, Trinity College Dublin.

The study, conducted by Sorcha Ní Dhubhghaill, looked at more than 200 patients with AMD and compared them with a group of more than 100 volunteers of the same age without the condition. Along with known lifestyle risk factors, it found that family history was also significant among those with the disease.

Blood samples from all the study’s participants were examined – specifically looking at single nucleotide polymorphisms (SNPs, pronounced “snips”), which Cahill describes as “little nicks in your genetic map”, three of which are associated with macular degeneration.

Sure enough, if the people studied had this change in the SNPs, they were more likely to be in the group with macular degeneration.

John Butler (77) gave little thought to the fact that his father and grandfather before him had vision loss until the first signs of AMD were detected in him during a routine eye test about five years ago. He only went for the test because he needed glasses; his arms, he says, had got too short to hold a book far enough away to read. He was referred to a leading consultant ophthalmologist, Prof Stephen Beatty in Waterford.

Then this time last year, when Butler, a retired commercial diver and boat-builder who lives in Dunmore East, Co Waterford, was on holidays in the Canaries, he noticed words starting to run into each other as he read.

“I thought I was going to go blind,” he says and he rang Beatty, who started treatment as soon as Butler returned to Ireland. He has been getting a monthly injection of medication in the one affected eye since.

“Now I can read without my glasses. It is really fantastic,” he says.

His father, who had the same problem in the 1960s, was not so lucky. He had an operation, for which he was given a 50/50 chance of success, but unfortunately it didn’t work and he became blind.

Hugh O’Brien (72), who is registered blind due to AMD, started having problems with his vision about 12 years ago. But as he had a more serious health issue, ulcerative colitis – a type of inflammatory bowel disease – at the time, he did not regard getting treatment for the eye as a priority. “It was only in the left eye and it didn’t seem that urgent.”

However, after having major surgery for the colitis in 2002, his vision began to deteriorate and the other eye became affected.

Despite laser treatment and injections into the eyes, he has lost all vision in his right eye and now has only peripheral vision in his left eye.

A retired secondary school teacher living in Cootehill, Co Cavan, O’Brien thought this was the end of his plans for various writing projects on local history. But, thanks to the “fantastic” work of the National Council for the Blind (NCBI), he now uses a computer fitted with a screen reader that speaks everything that appears on the screen.

Indeed, O’Brien says one of the positives of his condition has been this introduction to computers, which he believes he would have avoided for the rest of his life otherwise.

Now that the genetic change associated with AMD has been identified in Irish people, it should help to target more effective treatment, says Cahill, at a time when the number of people with AMD is bound to rise as Ireland’s population gets older and lives longer.

Although screening everybody for this genetic change is impractical, it would be very useful for people diagnosed with the first signs of AMD. If it was shown that they had this genetic marker, they could be watched more carefully because their vision is more likely to deteriorate faster.

Currently, the first thing newly diagnosed patients are asked to do is look after blood pressure and try to stop smoking. There are also oral pigment supplements (see panel) that can be taken, which have been shown to prevent progression to more serious forms of AMD in 25-30 per cent of people who have one eye affected.

But once you have signs of the more serious form of AMD, known as wet AMD, medicines need to be injected into the eye, which reduce the chance of progression by up to 90 per cent – and even bring about significant vision improvement in some cases.

“The earlier we get it and the better your vision is, the better chance you have that it won’t get worse,” adds Cahill, which is why one of the aims of the current AMD Awareness Week, running until this Sunday, is to spread the message that if people see any distortion – straight lines bent out of shape – they need to have an eye test immediately.

* See amd.iefor details of free testing available at various centres around the State this week

CALL FOR VOLUNTEERS: VISION STUDY

A major new study into the benefit of a nutritional supplement in preventing macular degeneration, and boosting vision in general, is looking for volunteers.

A scientific team at the Waterford Institute of Technology (WIT) has secured €2 million from the European Research Council to conduct what it describes as the first “gold standard” trial of the effectiveness of a supplement containing three naturally occurring plant pigments, which are found in the macular – the part of the eye that controls central vision.

Vision loss is caused by the thinning of these pigments. A pilot trial by the Macular Pigment Research Group at WIT has already shown that this pigment can be rebuilt “quite dramatically”, according to the principal investigator, Dr John Nolan.

Since about 2005, doctors have been recommending a food supplement containing pigments which give yellow vegetables, such as sweetcorn, their colour, but this will be the first double-blind, placebo-controlled clinical trial of its use, he explains.

A pigment found in marigolds, meso-zeaxanthin, is the crucial one, says Nolan. It was first used as a supplement to make eggs from hens in Mexico more colourful and later its anti-oxidant properties were recognised.

Next month the research team, managed by Nolan and consultant ophthalmologist Prof Stephen Beatty, will start recruiting patients with early-stage AMD who have not taken any supplement. They will also look for a second group of people over 18, without eye disease, to test the effect of the supplement on vision in general.

All participants will be required to visit WIT’s state-of-the-art vision research centre in Carriganore House to have their vision and eye health recorded before starting to take the supplement. They will then return for monitoring at six-monthly intervals over the next two years. None of the tests is invasive.


For more information, see mprg.ieor tel 051 845505.

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