Rhys Daniels, diagnosed as having the brain-wasting Batten's disease, was accepted for treatment at Westminster Children's Hospital in London, and a suitable donor was found earlier this year.
But counsel for the boy's father, Barry Daniels, said that uncertainty over the future of the unit, prior to closure of the hospital in March this year, had resulted in the loss of specialist staff which meant there were not enough to treat Rhys.
Yesterday Mr Daniels challenged the unit's closure, accusing Virginia Bottomley, Secretary of State for Health, Riverside District Health Authority and North West Thames Regional Health Authority of failing to follow proper procedures. Patrick Milmo QC, for the family, argued that the failure to consult the Riverside Community Health Council, the body legally entrusted to oversee health care provision, made the decision unlawful and so the unit should reopen.
The boy, from Epping, Essex, was found to be suffering from the disease - which leads to blindness, seizures and dementia - just over a year ago and was placed at the head of the list for treatment at Westminster Children's Hospital in July.
The bone marrow transplant was still experimental but appeared to be Rhys's only chance for life. The transplant must be carried out before symptoms of the disease begin, usually around the age of three; by the age of seven it is fatal. The Daniels' other child, a girl of five called Charlie, already has the symptoms.
Mr Milmo said that at the time of the unit's closure Rhys was the only patient awaiting treatment. The intention was that the unit should transfer to the new Westminster and Chelsea Hospital. But Mr Milmo said that sometime around June 1992 the thinking changed and a decision was taken not to transfer the unit because it was not treating enough patients to be economically viable.
Nicola Davies QC, for the health authorities, said that any order to reopen the unit would be impractical because of the vast cost and the difficulty of recruiting specialist staff.
Mark Shaw, for the Secretary of State, said that since she had not been involved in the decision Mrs Bottomley could not be held responsible.
Lord Justice Kennedy and Mr Justice Macpherson will make a ruling in several days.
Leading article, page 27