Each person has a unique “biological identity card”. It is the similarity between two biological identity cards that determines the compatibility between two people and the possibility of carrying out a transplant.
Each person has a unique, genetically transmitted “biological identity card”: the HLA system (human leucocyte antigens). This consists of a number of specific markers which, when compared between two people, determine their compatibility. This highly complex system has nothing to do with blood groups.
In theory, a patient in need of a transplant has a one out of four chances of being compatible with a brother or sister, since there are four different possible distributions of HLA antigens.
If there is no compatible donor among the patient’s siblings, it becomes necessary to search for a compatible unrelated donor. The transplant physician then asks Registre France Greffe de Moelle to search, both nationally and internationally, for a donor whose genetic characteristics are as close as possible to the patient’s ones.
The probability of compatibility between two people randomly taken is extremely low: 1 in 1,000,000 as average.
This is why each registration with the national registry counts, because it represents an additional chance of a cure for patients in need of a bone marrow transplant.