Human Chimeras

Some more interesting stuff from She Has Her Mother’s Laugh: The Powers, Perversions, and Potential of Heredity by Carl Zimmer… It turns out that Biology 101 contains a lot of simplifications (lies!).

Wikipedia: “A genetic chimerism or chimera … is a single organism composed of cells with distinct genotypes. In animals, this means an individual derived from two or more zygotes, …

How can this happen to a human and how does that interact with our “science is settled” attitude regarding DNA tests? Zimmer gives some examples:

In 2001, a thirty-year-old woman in Germany discovered she was a chimera while she was trying to get pregnant. For the previous five years, she and her husband had been trying to have a baby. They were fairly certain the problem didn’t lie with her biology, because she had gotten pregnant when she was seventeen and had had regular menstrual cycles ever since. A fertility test revealed that her husband had a low level of viable sperm, and so they made plans for IVF. As a routine check, the woman’s doctors took blood samples from her and her husband. They looked at the chromosomes in the couple’s cells, to make sure neither would-be parent had an abnormality that would torpedo the IVF procedure. The woman’s chromosomes looked normal—if she were a man. In every white blood cell they inspected, they found a Y chromosome. Given that she had given birth, this was a weird result. And a careful exam revealed that all her reproductive organs were normal. To get a broader picture of the woman’s cellular makeup, her doctors took samples of her muscle, ovaries, and skin. Unlike her immune cells, none of the cells from these other tissues had a Y chromosome in them. The researchers then carried out a DNA fingerprinting test on the different tissues, looking at the women’s microsatellites—the repeating sequences that can distinguish people from one another. They found that her immune cells belonged to a different person than her other tissues. It turned out that the woman had had a twin brother who died only four days after birth. Although he was unable to survive on his own, his cells took over his sister’s blood and lived on within her.

In 2003, a woman in Washington State named Lydia Fairchild had to get a DNA test. Fairchild, who was then twenty-seven, was pregnant with her fourth child, unemployed, and single. To get welfare benefits, state law required that she prove that her children were genetically related both to herself and to their father, Jamie. One day, Fairchild got a call from the Department of Social Services to come in immediately. A DNA test had confirmed that Jamie was the father of the three children. But Fairchild was not their mother.

When Fairchild was rushed to a hospital to deliver her fourth child, a court officer was there to witness the birth. The officer also oversaw a blood draw for a DNA test. The results came back two weeks later. Once again, Fairchild’s DNA didn’t match her child’s. Even though the court officer had witnessed the child’s birth, the court still refused to consider any evidence beyond DNA.

In Boston, a woman named Karen Keegan had developed kidney disease and needed a transplant. To see if her husband or three sons were a match, her doctors drew blood from the whole family in order to examine a set of immune-system genes called HLA. A nurse called Keegan with the results. Not only were her sons not suitable as organ donors, but the HLA genes from two of them didn’t match hers at all. It was impossible for them to be her children. The hospital went so far as to raise the possibility she had stolen her two sons as babies. Since Keegan’s children were now grown men, she didn’t have to face the terrifying prospect of losing her children as Fairchild did. But Keegan’s doctors were determined to figure out what was going on. Tests on her husband confirmed he was the father of the boys. Her doctors took blood samples from Keegan’s mother and brothers, and collected samples from Keegan’s other tissues, including hair and skin. Years earlier, Keegan had had a nodule removed from her thyroid gland, and it turned out that the hospital had saved it ever since. Her doctors also got hold of a bladder biopsy. Examining all these tissues, Keegan’s doctors found that she was made up of two distinct groups of cells. They could trace her body’s origins along a pair of pedigrees—not to a single ancestral cell but to a pair. They realized Keegan was a tetragametic chimera, the product of two female fraternal twins. The cells of one twin gave rise to all her blood. They also helped give rise to other tissues, as well as to some of her eggs. One of her sons developed from an egg that belonged to the same cell lineage as her blood. Her other two children developed from eggs belonging to the lineage that arose from the other twin. When Lydia Fairchild’s lawyer heard about the Keegan case, he immediately demanded that his client get the same test. At first, it looked as if things were going to go against Fairchild yet again. The DNA in her skin, hair, and saliva failed to match her children’s. But then researchers looked at a sample taken from a cervical smear she had gotten years before. It matched, proving she was a chimera after all.

More: Read She Has Her Mother’s Laugh: The Powers, Perversions, and Potential of Heredity

6 thoughts on “Human Chimeras

  1. Given examples such as these, and numerous others equally astounding throughout animal and plant biology, why is it so difficult for people to accept the relatively simple propositions of homosexuality and transgenderism?

    • I’m proposing that homosexuality and transgenderism is obviously a natural occurrence. Created by god even, if you’re into that sort of thing.

    • @Senorpablo:
      Totally acceptable, IMHO. But that’s not what the contention is all about.

      Most LGBT people mention that our society’s cultural norms are way too limited and rigid. The problem is not that some people want/need a status adjustment, but that the adjustment carries a non-trivial social/economic cost. A number of LGBT folks want the society to pay that cost, while most of their opponents refuse to chip in and suggest LGBT pay on their own. Simple as that.

      It’s exactly the same as with immigration. I am not trying to shift the focus of this discussion, just to mention a striking similarity.

      Most of us accept that immigration is a good idea, yet there is contention as to who pays for the implementation, including the benefits that accrue to the new immigrants. A long time ago when there was virtually no cost to absorbing immigrants (lots of unexplored territory, “free” land, and no social transfer payments) the US was an immigration magnet. This is no longer true. If we are willing to accommodate, say, 10 million “undocumented” immigrants p/a, 10 million of legal applicants will have to wait on line for yet another year. Is it their fault that they chose not to break US laws?

      Back to the LGBT issues. Most American Christians do accept the existence of religious minorities, e.g., Jews. I have no doubt they will also accept the LGBT, “sins” and all, as long as they are not taxed to pay for their practices.

  2. Reading about chimerism makes me want to pray and sends chills up my spine.

    I’m pretty sure Keegan was the subject of this JAMA article from 2002. RARE! “We are aware of only two other possible cases of human tetragametic chimeras with single cell lines in blood.”

    “A 52-year-old woman had renal failure as a result of focal sclerosing glomerulonephritis. In preparation for kidney transplantation, the patient and her immediate family underwent histocompatibility testing (Figure 1A). The results suggested that the patient could not be the biologic mother of two of her three sons, who had her husband’s HLA haplotype and a unique collection of HLA determinants, instead of one of the expected maternal haplotypes (Figure 1).”

  3. I’ve seen the claim that heterochromia (cf. max scherzer) is one eye having different DNA from the other. Also seen the claim that homosexuality is linked to an absorbed fraternal twin: literally pieces of female brain in male body and vice versa.

Comments are closed.