Thursday, February 7, 2008

What is HLA typing?

This is a very good question! HLA stands for Human Leukocyte Antigen (HLA) typing.

Many Shwachman-Diamond families have been HLA typed in case their SDS child needs to go to bone marrow transplant. HLA typing is also known as tissue typing and is done for solid organ transplants, too. HLA typing is not the same as your blood type. In fact, people who have the same HLA type may have different blood types. After a bone marrow transplant, the receipient usually becomes the blood type of the donor!

HLA typing can be done through a simple blood test or through buccal (cheek) swabs. Most hospitals do the testing via a blood test, while the National Marrow Donor Program uses buccal swabs to test donors.

The most likely place for someone to find a match is in their own family. A person inherits half of their HLA type from their father and half from their mother. I found a wonderful site that explains all of this. HLA FAQ

In our family, we were first HLA typed back in 2000 when our two Shwachman-Diamond Syndrome children came back with blasts (leukemia cells) in their bone marrow. We found out then, that only one of our children has a sibling match and that should the second child need a transplant, we would have to go to the NMDP registry to search for a donor. Later, in 2006, when doctors felt that the son without a sibling match might have to go to transplant, our family was re-typed to be sure he did not have a match. He was then run through the registry where there was no match found. They were able to find a few potential mis-matched donors, but it is not known if they would be suitable donors should he need a bone marrow transplant.

Our one son inherited a rare B3901 allele, thus making it hard for him to find a donor. While is other alleles are common, they are combined in an uncommon way, thus making his haplotypes uncommon.

This is all very confusing, isn't it? When this was all happening, I bought a book on HLA typing that was very helpful. It was interesting to learn just how rare this B3901 allele is! When testing for a bone marrow donor, they look at these HLA antigens: HLA A, HLA B, HLA C, and HLA D (DR). They will likely look at HLA DQ, as well... but the other four are the main HLA antigens that ae looked at.

Each person has two of each. Each person inherits one HLA-A from mom and one HLA-A from dad, so forth and so on. In order to be a match, the donor must have inherited the same exact antigens (allele) from his parents that the recipient inherited from his parents. When going through this testing, we learned that there is less than a 2% chance that a parent would be a match for their child and grandparents have even less of a chance. The HLA FAQ link above has the statistics for siblings and other family members.

For instance, the person in need of bone marrow transplant may have the following:

HLA A - 0101

HLA B - 1801

HLA C - 0701

HLA DR - 1101

HLA DQ - 0301

The donor must match at these numbers, inheriting the same antigens from his parents. For instance, the person above inherited HLA A 0101 from his mom and HLA A 1101 from his dad.

Our family held a bone marrow donor drive in March of 2007 at our church. Through this drive, we were able to get 122 people typed and added to the registry. We also know a Shwachman-Diamond family who had donor drive in celebration of the one a year anniversary of their son's bone marrow transplant. What a wonderful way to celebrate life!

I hope to eventually fill up this blog with all sorts of informational topics related to Shwachman-Diamond Syndrome. If you are interested in communicating with other SDS families and learning more, please feel free to visit the SDS Support Group page. Through this support group, parents and SDS patients have a wonderful forum for giving support and the exchanging information.