Rhys, of Epping, Essex, suffers from the rare, genetic condition Batten's disease, which can lead to blindness, severe disability and death. No child with the disease has survived beyond the age of seven and his sister Charly, five, is dying from it.
Now Rhys is in the Children's Hospital, Bristol, for his second transplant of donated bone marrow in just over a year. His first transplant, in July last year, was initially thought to be successful, but his own bone marrow eventually took over the donated marrow, his father, Barry Daniels, said yesterday.
'Since we learned in February that the new marrow had not taken over it has been a long wait for a second donor. It has been a very hard decision for us to have him take a second transplant. But we have to give him this last chance,' he said
Rhys's parents were earlier involved in a court battle with the Secretary of State for Health, Virginia Bottomley, over the closure of the bone marrow unit at the Westminster Children's Hospital, where he was due to have an operation. When that was cancelled, his case was transferred to the Bristol hospital.
Yesterday Rhys was undergoing chemotherapy treatment in preparation for the transplant procedure on Friday. He will stay in the specialised isolation unit at the hospital for up to eight weeks. It could be up to a year before doctors will know whether the new marrow has taken or not.
Mr Daniels said: 'So far Rhys is doing fairly well given his condition. Obviously we are very aware that the disease could kick in at any time.
'Every little thing that has affected him has created heartache that 'this could be it'. Some neurological tests have shown some worrying signs and we have to be very careful.'
He said that the new donor was unknown to him but had been found through the British Bone Marrow Donor Appeal, which has helped him campaign to find potential donors for Rhys.