Sights set on genetics

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.