Parental Testing For Chimeras

Chimera, best known to be a mythical creature with a lion’s head, goat’s body, and snake’s tail, also refers to a human with two different genomes.

Chimerism is a condition where a human has two different sets of DNA, that is, the human’s body contains two genetically different types of cells. This case is quite rare, and only a few persons are chimeras. Most of them go undiagnosed as chimeras can live their whole lives completely unaware of the fact that they are one. This accounts for the reason why there is no available data on how chimeras walk the Earth.

How Does Chimerism Happen?

✓ After a bone marrow transplant:

Getting a bone marrow transplant comes with a bonus package – new set of cells and a new name, genetic chimera. Bone marrow being a major center for the production of blood cells, gives the recipient new types of blood cells. This chimerism can either be complete or mixed. Complete chimerism is when the recipient’s blood cells are all of the donor’s. Mixed chimerism, however, is when the recipient’s blood is a mix of the recipient’s and donor’s DNA.

✓ During normal pregnancy:

This happens when pregnant woman retain some cells of the fetus that leave the uterine environment. This is more accurately referred to as microchimerism and experts in this field believe that this is likely the case with most normal pregnancies. The 2010 study conducted by Gammill and Nelson, showed that maternal-fetal microchimerism may in fact be the most common type of chimerism in humans.

✓ Fraternal (dizygotic) twins pregnancy:

When one embryo absorbs the cells of the other dead embryo. The death of the other embryo occurs very early in the pregnancy, so it often goes unnoticed and the pregnancy is taken to be a single birth pregnancy. Ultimately, the other embryo ends up as a child with two sets of DNA.

Chimerism In Parental Testing

With very few cases of chimerism induced parental confusion noticed, one can only wonder what the actual statistics are. Chimeras, when faced with parental testing (paternal or maternal testing), might receive false exclusive results – results saying that they are not the parent of the child in question, when they actually are.

Being a Chimera means some of the cells in your body are yours and the others are not. Sometimes, the DNA of your ovaries (or testis as the case may be) will be that of the absorbed dead embryo, as was in the case of Karen Keegan. Karen Keegan was discovered to have a set of genes in her ovaries that were different from the set of genes in her blood. Thus a maternity test with her kids gave false exclusive results, her story was entered as a report in New England Journal of Medicine in 2002.

A similar thing happened to a 34 year old US man who had a set of genes in his saliva different from the ones in his sperm. Another case sprung up with Linda Fairchild and in all these cases, a relationship could be shown between the Chimera parents and the children. For some, it is an uncle-nephew relationship, for others, the relationship could get quite complex.

Those in the medical community can only wonder just how many parental testings gave false exclusive results, and whether they were induced by chimerism. Though this condition is not yet prevalent, some genetic experts think they might be more common than we think. With more cases being reported, chimerism will find its way into the spotlight.

The rise in multiple births boosted by ART (assisted reproductive technology) may also pave way for more chimeras, knowing fully well that some multiple birth pregnancies end up as single birth pregnancies. The damage caused by chimerism induced parental confusion to homes is probably irreparable; but then, future damage can be prevented if more research is done on the topic, especially with easier ways to diagnose chimerism. Chimerism can also create problems for fertility clinics where the parental confusion can be taken as a case of sperm mix-up, like in the case of the 34-year-old US man.

Gold was once considered rare, but these days every jewelry store has gold jewelry. For now, chimeras are rare but just how rare will they be in the future?