Part I—Haplotypes

“You know, Karen, something very unusual has happened here. We’ve tested your sons because they were possible donors. Your sons’ blood does not match your blood and that’s an impossibility, so they couldn’t be your children…these could not be your children.”

Karen’s hand shook as she listened to the nurse on the telephone tell her that two of her three sons could not possibly be hers. Karen, who was 52 years old, was in need of a kidney transplant. She and her sons had undergone blood tests to determine if they were suitable donors.

The tests determined their human leukocyte antigen (HLA) genes, some of which encode cell surface recognition proteins that the body uses to distinguish its own cells from foreign material. Because there are hundreds of different versions of the 200+ HLA genes, each person’s combination is almost unique. However, because these genes are located in a group on chromosome #6, they are often inherited together in a block known as a haplotype (see Figure 1).

Because a transplanted organ is seen as foreign tissue to a host’s immune system, it is important to try to “match up” as many of these genes as possible to minimize the rejection of the new organ. The chance of matching is highest among related individuals.

The nurse told Karen that her lab report results indicated that her HLA haplotype is type 1 and 3 and her three sons were types 2 and 5, 2 and 5, and 1 and 6, respectively.

Questions

1. How many HLA haplotypes should this woman’s sons each share with her?
2. According to these data, which sons cannot be hers?
3. What are some hypotheses to explain these data? Write down as many explanations as you can, no matter how far-fetched.
4. What tests should be done next to evaluate your hypotheses?

Date Posted: 09/01/07.

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