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Closer to a Cure
CHORI Researchers Identify Subdivisions in the U.S. Bone Marrow Donor Pool
In a new study published in Human Immunology, CHORI scientist Steven J. Mack, PhD, and his colleagues provide essential new clues that will help better identify potential matches for patients requiring unrelated bone marrow stem cell transplantation. The study utilized high resolution DNA sequencing to identify genetic variants associated with different ethnic backgrounds.

"In some cases, it may help to have information on a donor's ethnicity or national origin, so that when a patient self-identifies as Italian American for example, we which know which volunteer donors to look at to find a match," explains Dr. Mack.

”Ultimately we want to be able to best serve the transplant patient community by being able to get a high quality match from a donor pool.”

Currently, over 15 thousand patients a year are looking for their perfect donor match to cure their life-threatening diseases. Many of them won't find that match.

"There are basically five genes that are involved in determining a patient's compatibility with that of a potential transplant donor," Dr. Mack says. "Everyone has two copies of these five genes and ideally you want your donor and your patient to have a 10 out of 10 match."

Using the National Bone Marrow Donor Program registry – a national archive of tissue samples from individuals who have volunteered to be bone marrow donors – to find a donor who is a perfect match for an individual patient can be a bit like searching for a needle in a haystack. While doctors generally have a great deal of information about the genes of the patient, they often only have a minimal amount of information on the donors.

"The information in the registry is what we generally call low resolution in terms of how well a particular donor will match a particular patient because you don't want to go through the cost of high resolution analysis for a donor who might never be needed," explains Dr. Mack.

As a result, researchers are looking for ways to narrow down the field to a more likely – and smaller – pool of potential donors from which to select samples for additional, high resolution testing in order to bring patients in need that much closer to finding a match, and ultimately a cure.
“We already know that there are certain combinations of genes that are only found in certain parts of the world. In some cases, identifying whether potential donors come from those parts of the world can help us better identify possible matches.”
The largest segment of the donor population in the national donor registry is European American, so Dr. Mack and his colleagues chose to study two subdivisions within the European community – Americans of self-defined Spanish ancestry and self-defined Italian ancestry – to find out how these subdivisions were best characterized from a genetic perspective.

The results were surprising: the genetic make-up of Spanish Americans was quite distinct from that of the general European American population, and was in fact much more similar to that of Mexican Americans and other Hispanic or Latino Americans, while the genetics of Italian Americans were essentially equivalent to that of other European Americans.
"The most important conclusion that can be drawn from our results is that self-identified ethnic identities don't necessarily correlate with the population genetics that we see for these groups," says Dr. Mack. "This means that including self-identified ethnicity from a donor may not always be a useful surrogate for the genetic makeup of that donor when it comes to finding a perfect match."

The data also suggest that if ethnicity is going to be included as part of the donor information, those collecting the samples from the donors may need to be much more specific about how they ask about ethnicity in the donor pool, including asking about the donor's parents' and grandparents' background.

"Being able to understand how demographics and genetics interact is more critical than ever as donor registries get larger and more international connections are made between registries," Dr. Mack says.

"The better the chances of a donor matching a patient,
the faster the patient gets that transplant, and the greater their chances of survival."

Dr. Mack and his colleagues are helping increase those chances with their latest study, bringing doctors that much closer to finding a patient's perfect match faster and more efficiently than ever before.

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Tuesday, May 17, 2011 8:19 AM

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