Understanding the Data

All patients whose haplotypes are at present seriously under-represented in US and international registries face extra challenges when in need of an unrelated BMT donor. Not only does the fact that mixed heritage patients face more difficulty  finding a match cause extra stress, but often misunderstandings may arise about the reasons behind the situation. In general terms, it is a matter of representation.

The popular use of the terms “race,” “ethnicity,” and “minority” can contribute to the confusion on the topic. It is correct to say that people in the US who are identified as members of racial/ethnic minority groups, including mixed heritage individuals, are under-represented in the present US and international donor registries. This is also true for some people who are categorized as Caucasian according to Census Bureau definitions. However  this does not necessarily mean that a given  individual of such personal heritage has rare haplotypes or that a rare type of donor is needed for him or her.

A quick look at the composition of the world’s population shows that what is rare is the representation of certain haplotypes linked to specific historical genetic-origin populations in donor registries. In much of the US too, the numerical definition of which groups are in the “minority” and “majority” groups is rapidly changing, but the donor registry does not yet reflect our demographics.

Other relevant factors are that the incidence of specific haplotypes varies across and within members of specific genetic-origin groups, and that the combinations of human haplotypes that can occur are very many. There is also no set pattern for the inheritance of the alleles that form the haplotypes; in other words it is a random, unpredictable process. HLA typing will reveal  which alleles and groups thereof have been inherited. for mixed hertiage patients or donors, their genetic “profile” by DNA or may not correlate to an  identification based on physical appearance or social identity.

In addition, patients of African ancestry have the most difficult time finding an unrelated donor. According to researchers studying the genetic origins of humankind, such as Kenneth Kidd of Yale University, human life began in the continent now known as Africa. A great variety of haplotypes and combinations thereof, arose within the historical population there. While the dispersal of these haplotypes around the world has been relatively limited, the effects of the African diaspora have added more genetic diversity to these. Therefore it will take proportionately many more prospective donors of African ancestry, including mixed heritage anecstry, in the pool, to be able to find a donor for any one patient of African descent.

This is part of the reason why there is now so much interest in utilizing umbilical cord blood for transplantation, as its less mature cells seem to be more adaptable, and allow for increased flexibility in haplotype matching.  However the composition of the cord blood donor pool still needs to increase significantly in both size and diversity. Also needed is continued recruitment of diverse blood and marrow donors, and whose genetic origins need to be tracked for equity purposes.

While we are fully aware of all the horrific past and present ways that scrutinizing of ancestry has been used for oppression around the world, there is a need for a information on the composition of our donor registry. This information is also vitally needed to best guide donor recruitment efforts. Currently, in addition to the official federal race and ethnicity categories, the NMDP data on donor pools  includes a a single  “multi-race” or “multiracial” category.  However, use of a single “multi-race” category is  not consistent with the Census Bureau’s system of  tracking US population demographics.

In 2000, the US Census Bureau began allowing people to mark “all that apply” for their own race(s) and ethnic origin(s), and it reports the precise results of heritages listed by  respondants. The Census also offers periodic  summary reports on the US population, including on  total numbers of people who report being of  2 or more races. However  the Census Bureau does not use multi-race or multiracial as a category group name,  While we are  well aware of the limitations to the current  Census categories , we also believe that it is important to accurately report on the  genetic heritage composition  of the BMT donor pools  for all cell sources. This information is also needed for planning equitable donor recrutiment strategies.  For the sake of present and future patients in need, it is critical that the actual  diversity of  mixed heritage donors be recorded.

Advertisements