The Quest for a Donor: Probability Based Methods Offer Help.
When a patient in need of a stem cell transplant has no compatible donor within his or her
closest family, and no matched unrelated donor can be found, a remaining option is to search
within the patient’s extended family. This situation often arises when the patient is of an
ethnic minority, originating from a country that lacks a well-developed stem cell donor
program, and has HLA haplotypes that are rare in his or her country of residence. Searching
within the extended family may be time-consuming and expensive, and tools to calculate the
probability of a match within groups of untested relatives would facilitate the search.
We present a general approach to calculating the probability of a match in a given relative, or
group of relatives, based on the pedigree, and on knowledge of the genotypes of some of the
individuals. The method extends previous approaches by allowing the pedigrees to be
consanguineous and arbitrarily complex, with deviations from Hardy-Weinberg equilibrium.
We show how this extension has a considerable effect on results, in particular for rare
haplotypes. The methods are exemplified using freeware programs to solve a case of practical