Home » Reference » Chimerism is a Condition When an Individual is Born with Two Sets of DNA Because They Absorbed Their Twin While Still in the Uterus.

Chimerism is a Condition When an Individual is Born with Two Sets of DNA Because They Absorbed Their Twin While Still in the Uterus.

Chimerism happens when a woman is pregnant with twins, and one of the embryos dies. The other embryo then absorbs its twin’s cells. Experts are not sure how common the condition is since there are only 100 documented cases. But do you know what chimerism really is?

Chimerism is a disorder in which people are born with two sets of DNA, This occurs because they absorbed their twin while still in the womb.

How Common is Chimerism?

Experts are unsure of the global population of human chimeras. However, the syndrome is thought to be fairly unusual. It may become more familiar with some fertility treatments, such as in vitro fertilization, although this has yet to be established.

Only a few hundred occurrences of chimerism have been documented in modern medical literature.

Nonhuman animals can be affected by chimerism. It frequently results in two different sorts of colorings on opposite portions of the same animal, such as two different-colored eyes. (Source: Healthline)

What Causes Chimerism?

There are various types of chimerism that people can experience. Each has a somewhat different cause and may manifest differently.


Chimerism usually happens in humans when a pregnant mother absorbs a few cells from her fetus. It is also possible for a fetus to absorb a few cells from its mother.

These cells may enter the bloodstream of the mother or fetus and move to many organs. They can live in a mother’s or child’s body for a decade or more after delivery. This is referred to as microchimerism.

Artificial Chimerism

When a person has a blood transfusion, stem cell transplant, or bone marrow transplant from another person, they may absorb part of that person’s cells. This is known as artificial chimerism.

In the past, artificial chimerism was more widespread. Transfused blood is typically treated with radiation nowadays. This allows the transfusion or transplant recipient to absorb the new cells more effectively without permanently integrating them into their body.

Twin Chimerism

When a pair of twins are conceived, one embryo dies in the pregnancy, and a more extreme form of chimerism occurs. The surviving fetus may absorb part of its deceased twin’s cells. The surviving fetus now has two sets of cells: its own and some of its twin’s.

Tetragametic Chimerism

Human chimeras can also form when two separate sperm cells fertilize two different egg cells. The cells then fuse to form a single human embryo by crossing cell lines. This is referred to as tetragametic chimerism.

(Source: Healthline)

What are the Signs and Symptoms of Chimerism?

Chimerism symptoms differ from person to person. Many people with this disorder have no symptoms or do not recognize them as chimerism. Among the symptoms are:

  • Hyperpigmentation or darker skin, or hypopigmentation or lighter skin in localized patches or throughout broad parts of the body
  • Two eyes of different colors
  • Genitals with both male and female parts or that appear sexually ambiguous. This sometimes results in infertility.
  • Two or more pairs of DNA are found in red blood cells of the body
  • Autoimmune disorders, such as those affecting the skin and neurological system

(Source: Healthline)

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