When Mary MacAodha gave birth to her last child, she and her husband, Mairtin, were devastated.

"It's not what you expect," she says. "Okay, you hear about it, worry about it, but it's always someone else. You worry about it from a distance, as if it really can't happen to you. Then when it does happen, your expectations are totally thrown and you're left with a huge fear of what the future will bring you."

MacAodha's youngest son was born with Wolf-Hirschhorn Syndrome, an extremely rare disorder that causes severe mental and physical disabilities. Now 13, Niall cannot speak, cannot care for himself, is fed through a feeding tube and only learned to walk two years ago. MacAodha had to leave work in order to care for her son around the clock.

"We didn't know what we were doing," MacAodha says of the first few years of her son's life. "We got very little sleep. We were punch-drunk all the time, trying to get over one hurdle and then another. "It got to the point where a new doctor would come along and want to test him for something else and we would tell them not to bother - we were having enough trouble dealing with the things we knew about."

And Niall's condition wasn't the only difficulty his parents had to face. With their youngest child going in and out of hospital and needing 24-hour care, there was very little time left over for the MacAodhas' older children, Aileen, now 17, and Eoin, 16. Fortunately, the family wasn't working alone. Mary MacAodha's parents became second parents to Aileen and Eoin, and helped to provide them with a consistent flow of love and attention.

"They had a huge amount of involvement," MacAodha says of her mother and father. "They gave us so much support, and they really provided a level of stability that we all really needed. And the result is that the other children do not resent Niall at all, and they could. "In fact, my son was saying the other day that if we take an outing without Niall, it just doesn't feel like we're a complete family."

The MacAodhas have been fortunate in other ways as well. Since he was young, Niall has left the house every day to go to St Michael's House in Kilmacud, Dublin, where he receives physical and occupational therapy. He also works with a teacher every day on stimulation programmes that motivate him to walk and move around.

And since last year, Niall has spent four nights a week at the Children's Sunshine Home in Leopardstown, Dublin, a full-care facility designed for children with severe disabilities. The Sunshine Home allows full access for families, which means that the MacAodhas can visit him at any time - and can take him away for periods without worrying that he will lose his place.

"It's really the best possible care situation," MacAodha says. "And we can already see a tremendous improvement in him since he started going there. Now he is far more aware of his surroundings. And he's much more sociable, he really likes being around people, watching them, and having them talk to him. "We can also see that there is a change in his character as well - he's becoming more assertive now that he has to compete with a few other people for attention."

Nowadays, Niall spends three nights a week at home, beginning on Fridays. And though his family sees a little less of him, the time away helps them to appreciate his visits all the more. "We can enjoy him a lot more because we're not so exhausted."

One might think that with Niall away more often, Mary MacAodha might simply take a long, deserved rest. Instead, she is using her time to help families like her own.

"We are extremely lucky," she says. "We now have a place for Niall - we know he will be taken care of even after we are gone - but a lot of families are not as fortunate. They have so much pressure on them, and a lot of them can't cope."

Consequently, Mary MacAodha is working with a number of groups, including the National Parents and Siblings Alliance, which is pushing for legislation that will recognise the rights of disabled persons and that will insure their futures.

"It's the Government's responsibility to care for the citizens of the state. It's just that some of them need more care than others."