Overview of Chimera

Ancient Greek mythology has tales of a fire-breathing monster known as a chimera, which means “fire eater.” This terrifying creature was a cross between a lion, a goat, and a snake.

The term “chimera” refers to a person made up of two genetically separate kinds of cells. Human chimeras were identified for the first time with the introduction of blood typing when it was revealed that certain people possessed more than one kind of blood. In most cases, they were found to be “blood chimeras” — non-identical twins who shared a blood supply in the uterus. Chimeras account for around 8% of all non-identical twin pairs. Some believe that those who were not twins contain blood cells from a twin who died early in pregnancy. As a result of their shared placental blood supply, twin embryos can often transfer their blood stem cells to the bone marrow of their sister.

The number of micro-chimera is increasing. These individuals have lower quantities of foreign blood cells that may have traveled from mother to child via the placenta or remained after a blood transfusion. Additionally, the use of in vitro fertilization (IVF) contributes to the increase in human chimeras. For improved success rates, two or more embryos are implanted in the uterus simultaneously, resulting in more twin pregnancies than is typical among women who undergo IVF. More twins equate to more chimeras, and vice versa.

Signs and Symptoms of Chimerism

The signs and symptoms of chimerism differ from one individual to the next. Many people who have this disorder may not display any indicators or may not identify the abnormalities caused by chimerism. Some symptoms include hyperpigmentation (increased skin blackness) or hypopigmentation (increased skin lightness) in tiny patches or over regions as big as half the body. Other signs and symptoms include:

• Two different-colored eyes

• Genitals with both male and female components (intersex) or genitals that seem to be sexually ambiguous (this sometimes results in infertility)

• The possibility of autoimmune disorders, such as those affecting the skin and nerve system,

What is the Procedure for Diagnosing Chimerism?

Most of the time, people learn they are chimeras by chance. On the other hand, chimerism has been detected via genetic testing for medical reasons other than chimerism, such as organ transplantation. Chimerism is characterized by the presence of several sets of DNA in circulation. When a person’s blood cells have DNA that is not present in the rest of their body, genetic testing may assist in determining whether or not they are sick. However, since the illness is uncommon and individuals are seldom checked for it, individuals can live their entire lives without realizing they are chimeras.

What is the Prevalence of this Condition?

Professionals are not sure of the exact number of human chimeras that exist across the globe. However, it is regarded as a rather uncommon disorder. It’s possible that some reproductive procedures, like in vitro fertilization, are making it more frequent, but this hasn’t been established.

According to the most recent estimates, only a few hundred instances of chimerism have been documented in the contemporary medical literature.

Nonhuman animals may be affected by chimerism as well. It often results in two separate sorts of coloring on opposite portions of the same animal, such as two different-colored eyes on the same animal.

What Causes Chimerism?

There are various different forms of chimerism that people might experience. Each has a somewhat different underlying reason and may manifest itself in a variety of ways.

Chimeras are Created by Humans (Organ Transplantation)

It turns out that one sort of chimera is extremely prevalent. Anyone who has had an organ or bone marrow transplant is a chimera in the truest sense of the word. Each of these treatments involves the recipient obtaining cells (and DNA!) from another individual. This is called cell donation.

The objective is for the donor cells to remain in the recipient for an extended period of time. This means that the recipient will have two sets of DNA: their own (which will constitute the majority of their body) and the donor’s (which will constitute the remainder of their body) (in the donated organ). In the event that you have ever had a blood transfusion or an organ transplant, you may be a man-made chimera! For example, the DNA in the blood of a bone marrow recipient will be different from the DNA in the rest of the recipient’s body. If we ever needed to look at their DNA directly, we may have to seek other sorts of the tissue rather than blood if we wanted to do so.

Micro-chimerism as a Result of Pregnancy

In the majority of moms, who turn out to be a small bit chimera, it turns out that in the course of pregnancy, certain cells are transferred between the mother and the fetus. The vast preponderance of these cells die, but rarely a few may survive and reproduce. If this is the case, the mother basically has a few cells that have the DNA of her child.

Because the amount of interaction is quite modest, this sort of chimerism is referred to as microchimerism. To put things in perspective, there may be one fetal cell for every 500,000 maternal cells to give you a concept of the scale.

The presence of a micro-chimera in the body of a previously pregnant woman may be detectable. Maturity is not guaranteed, but cells from the fetus may sometimes be discovered in the mother’s bloodstream. It may be feasible to distinguish them from the mother’s blood if they exhibit traits that are distinct from the mother’s blood. However, this is not always practicable, particularly if the cells exhibit properties that are similar to one another. If you can locate any and separate them from the mother’s cells, you might compare the DNA from the two sets of cells. You would then be able to observe that the genetic code had changed. Keep in mind that we all have our own distinct DNA!

Chimerism Fusion

This is a term used to describe the process of combining two or more things into a single entity. While pregnant with twins, if one of the babies dies in the womb, it is possible that some of the cells from the dead twin will be absorbed by the remaining baby. If this occurs, the surviving fetus will have two sets of DNA: its own DNA as well as DNA from its sister or brother.

This sort of chimerism may be seen in what is known as the “vanishing twin” phenomenon, which occurs when a person’s twin disappears. This refers to the condition in which a fetus dies in utero during a multi-gestational pregnancy and is partly or entirely absorbed.

People who have chimerism seldom exhibit any outward symptoms of having two separate sets of DNA in their bodies. If you have two different colored eyes or two different skin tones, it’s probable that you’ll notice some visible indicators of infidelity. In fact, each of these things may occur in non-chimeras as well.

Because the placement of cells from one’s twin throughout the body might be arbitrary, it is possible that one does not realize that they have absorbed their sibling!

An analysis of your DNA might show whether or not you’re a chimera, according to the National Institute of Health. You should be able to tell the difference if your blood contains cells from your “twin,” but your saliva contains DNA from yourself. If you matched the DNA in your saliva to the DNA in your blood, the samples might seem to be from “siblings” rather than from the same person, depending on how you performed the comparison.

However, it is possible that your DNA is present in both your blood and saliva, while DNA from your “twin” is present in your spleen. A comparison of blood and saliva would have missed the second set of DNA in this instance! In order to find your twin’s DNA, you’d need to get a sample of tissue from your spleen.

As a result, detecting chimerism might be very difficult. It is conceivable that you may be instructed to undergo testing for a variety of other tissues as well.

Occasionally, individuals come to the realization that they are chimeras by mistake. There have been a few instances when a parent has “failed” a DNA test, even if the kid is absolutely their own.

The DNA from the cells that produce sperm or eggs will be passed on to a kid. A parental DNA test, on the other hand, normally takes the DNA of the parent through a cheek swab (or blood sample). An aunt or uncle will be identified based on a DNA test if the child’s sperm or egg cells have DNA from one “twin” and his or her cheek cells contain DNA from the other “twin.”