Why can't the patient's family help instead?

Why can't the patient's family help instead?

Paul Travers (Deputy Director of Research) gives expert video advice on: What is bone marrow?; Who needs a bone marrow transplant?; Why do you need more donors and who can become a donor? and more...

Well if there's a matching family member then they can, and there's basically a 1 in 4 chance that a brother or sister could be a match for you and that would be the best match, for any patient, would be a matching brother or sister. But if you haven't got a matching brother or sister, if you're a single child in a family or your brothers and sisters don't happen to match then you have to find somebody else, so you have to look in the general population for somebody whose going to be a good match for you.