The parents of a toddler born with a serious medical condition that baffled experts have spoken of their joy after discovering their new baby's blood type could help transform his life.
Ben Johnston, from Waringstown in Co Down, spent the first 17 months of his life in intensive care.
Expert doctors from Great Ormond Street at one point said he would not live past his first birthday.
But Ben, now three-and-a-half, defied the odds and his family are waiting to see if stem cells taken from baby Harry could help give him a new lease of life.
Ciara and Andy Johnston had the stem cells – known as the building blocks of life – taken from the placenta when he was born in July.
However, in order to be a suitable stem cell donor, Harry has to be both a blood match and a tissue match.
After waiting a number of months the family were told the good news that they were "one step closer" with the brothers having a matching blood type.
"Ben is A+ and so is Harry. It is a positive start," Ciara said.
"Despite more testing and research needing to be done to see if they can used, we believe this is a step in the right direction."
Ben has a healthy twin brother, Leo, and was finally diagnosed with a rare condition – called Pons Hypoplasia – by doctors at the Royal Belfast Hospital for Sick Children.
The little boy's condition means he is ventilator-dependent 24 hours a day and has had a tracheostomy, enabling him to breathe through a tube.
He also feeds through a tube in his stomach.
The condition affects Ben's brain development and has left him needing 24-hour care.
He is understood to be the only child in the UK with the condition.
Stem cell treatment could help with his development.
The family decided to try the treatment after discovering they were expecting their third child –a baby they never thought they could have.
The Johnstons conceived the twins after undergoing fertility treatment, and thought they could not become parents again.
Ciara, a nurse, said being told they are a blood match has left them "over the Moon".
"We were sort of hoping that no news was good news," she said.
"Andy and I are different blood groups. There was a chance he would be Andy's blood group, so he wouldn't match Ben at all.
"There is a thing called tissue typing as well. They haven't told me that. So that is the next stage, but it is very positive. We remain positive and hopeful."
STORY SO FAR
Ben Johnston was born three-and-a-half years ago. His parents were told not to expect him to live past his first birthday. After 17 months, he was finally diagnosed with the rare condition Pons Hypoplasia. If stem cells from his brother Harry match, it could help his development. A charity called Ben's Fund aims to help children who rely on a life support machine for survival. See www.bensfund.co.uk for more information.