Great Ormond Street has announced a major fund-raising drive to raise £66m to build and equip a centre for children's rare disease research.
John Connolly, the chairman of the fund-raising team, said: "The scientists and doctors I've met from the hospital are just starting to unlock the potential of 21st Century medicine.
"But they need our support so that they can grasp the unique opportunity in front of them and accelerate their valuable work to help many more children with many different conditions, some of whom still have little hope of diagnosis or treatment, let alone a cure."
The news comes as the Department of Health published a consultation document about the first ever UK plan on rare diseases.
They said earlier diagnosis of rare conditions and better co-ordinated care would improve the quality of life for people with such diseases.
Health Minister Lord Howe said: "The UK has a good story to tell about supporting and treating people with rare diseases. But we know the challenges people face and that there is always room for improvement.
"This is the first time the UK has had a coherent set of proposals on rare diseases which outlines how we can build on our strengths through improved co-ordination of services, stronger research and better engagement with patients and their families."