Brother #1 just received the news that he is also a match!
Yet, he is not as good of a match as Only Sister. A more detailed explanation requires a vocabulary lesson.
HLAs, short for Human Leukocyte Antigens, are used to determine whether a donor is a good match. HLAs are proteins located on a person’s white blood cells and other tissues. A person has a few hundred of these proteins in his/her body. For ease, they are grouped into 3 categories: A, B, and DR.
A person receives an A, B, and DR makeup from his/her father and a different A, B, and DR from his/her mother. The chance of a sibling matching Kathy’s exact HLA makeup is 1 in 4. Thus far, nobody has been an exact match.
Brother #1 matched 1 of 6 HLAs.
Only Sister matched 3 of 6 HLAs.
Thus, Only Sister remains the front liner.
For a more detailed explanation of HLAs, please read this article published by Stanford.
