Chimerism: The rare phenomenon of two sets of DNA
When it comes to ranking the discoveries of modern medicine, DNA is pretty high up there. There are few discoveries with wider applications than DNA, which we use for everything from identifying blood relatives to presenting evidence in court. DNA is so useful and has so many applications because it is always unique to the individual. Using DNA testing we can always pinpoint a single individual. Or can we?
Introducing chimerism: a genetic phenomenon that allows one individual to have two sets of DNA. Check out this gallery to learn all about it.
DNA
Ever since DNA was first discovered towards the end of the 19th century, it has proven itself useful in more ways than we could ever possibly have imagined.
Why is it so useful?
DNA is so useful because, the overwhelming majority of the time, each individual is composed of cells that are made from DNA unique to them.
Introducing chimerism
A genetic chimerism, or chimera, is a single organism that contains the cells of two different and distinct individuals. Its body contains two sets of DNA.
Rare phenomenon
Although it is extremely rare (only around 100 cases have been recorded in modern medical literature), chimerism can affect humans as well as plants and animals.
Different types of chimerism
There are four types of chimerism: microchimerism, artificial chimerism, twin chimerism, and tetragametic chimerism. Each has a different cause and potentially different symptoms.
Microchimerism
The most common way for microchimerism to occur is for a pregnant mother to absorb some of her fetus’ cells, or vice versa.
If this happens, the new cells may be absorbed into the bloodstream of their new host and travel to the organs. They can remain in the body for up to a decade.
Artificial chimerism
This is called artificial chimerism and, although it happens, it used to be more common in the past. Nowadays donated organs are treated with radiation to stop this from happening.
Twin chimerism
Finally there is tetragametic chimerism. This occurs when two sperm cells fertilize two egg cells, and then these cells all fuse together to form a single embryo.
Skin symptoms
More common symptoms include hyperpigmentation or hypopigmentation. These present as either patches of darker or lighter skin across areas up to half of the body.
Non-visible symptoms
Other symptoms include red blood cells that contain two or more sets of DNA, and possible autoimmune diseases, particularly those related to the skin and nervous system.
Left to chance
More often than not, chimerism is discovered by accident when a person undergoes genetic testing for an unrelated reason, such as an organ transplant.
Failed paternity test
In 2015, the Independent reported on a 34-year-old male chimera who failed a paternity test because the DNA in his saliva was different from the DNA in his sperm.
Failed maternity test
In another high-profile case, this time from 2006, a mother failed a maternity test because she was a twin chimera. The DNA in her egg cells was different from that in other cells in her body.
Taylor Muhl
More recently, in 2018, Californian singer Taylor Muhl revealed that she was a twin chimera. Her main symptom is having two different shades of skin on her torso.
Bone marrow transplants
Following a bone marrow transplant, the person who received the bone marrow will have a mix of DNA: some of their own and some from their donor.
Pregnancy
Although it is extremely rare, researchers believe that it is possible for microchimerism in the direction fetus to mother to occur in almost every pregnant mother.
