It is an act of gratitude, and Nathan Hartley is only too happy to perform it.
Nathan aged 13, is one of four brothers, all who had been diagnosed with X-linked lymphoproliferative syndrome, a rare genetic defect, in November 2003.
X-linked lymphoproliferative syndrome has affected around 100 males worldwide.
Life expectancy is very low in those diagnosed with this. The disorder causes the immune system to respond abnormally to some viral infections and the only cure is bone marrow transplant.
While women can carry this condition they cannot be affected by it.
This March, Nathan will become a donor, to save his younger brother's life.
The procedure of bone marrow transplant involves destruction of the patient's bone marrow with chemotherapy followed by blood transfusion given intravenously from a healthy donor. The donor will be put on drugs to increase the concentration of stem cells released into his or her blood.
The donor's blood will then be drained and stem cells removed, with the filtered blood returning to the donor, simultaneously.
The guest stem cells transfused to the recipient then find their way to the bone marrow and start producing other stem cells.
When four sons of the Hartley family were diagnosed with the rare disorder, there was a nation wide appeal through the Andrew Nolan trust. The Hartley boys were not expected to live beyond their teens.
Thousands responded to the appeal and the first son Joshua, 14, was able to get a donor.
The operation was performed by one of Britain's most famous children's hospital; the Great Ormond Street Hospital.
The second son Nathan had peripheral blood stem cells donated from his mother while the third son Daniel, 10, underwent bone marrow transplant from another donor.
Now Nathan's recovery is so marked that he is fit and healthy enough to be a donor himself, to his little brother, Luke.