The vanishing DZ twin and the chimera

This man was found to be a chimera of himself and his vanished twin sister, 40 years after his birth.

We report the case of a 40-year-old man diagnosed with a scleroderma-like disease. Clinical similarities with graft versus host disease prompted initial testing for chimerism employing fluorescence in situ hybridization (FISH). Female cells were observed within peripheral blood mononuclear cells from the patient.

Because maternal cells have been detected in healthy immunologically competent adults and patients with autoimmune conditions, we hypothesized that these cells were of maternal origin. Contrary to our expectations, HLA-specific quantitative PCR (QPCR) ruled out maternal microchimerism. However, HLA-specific QPCR testing was positive for the paternal HLA haplotype that the patient did not inherit. We reasoned that the most likely origin of chimerism with non-inherited paternal HLA alleles was from an unrecognized “vanished” twin. The patient had never received a blood transfusion.

This report suggests that cells from a vanished twin are a possible source of chimerism. The frequency of chimerism from this source is not yet known and whether the scleroderma-like disease observed in the patient is anecdotal or implies a potential association with autoimmune disease remains to be elucidated.

 Read whole article here

The chimera - the twin inside me

Here is an article about the twin inside me  - a chimera

Lydia Fairchild was twenty one when she had her first baby. Despite being separated from the baby's father, Jamie Townsend, she and Jamie had a second baby a year later. Another year on and and she became pregnant for the third time after which she and Jamie split up again. With no steady work and unable to support herself and the children she applied for state benefit.

Her world was about to be turned upside down.

The State Prosecutor's Office required DNA tests from Jamie to prove that he was the father of the children and, as a matter of course, Lydia was also tested.
In December 2002 she received a phone call from the prosecutor's office asking her to come in for the results. This was unusual and it soon became apparent why. The results confirmed that Jamie was the father but they also revealed that Lydia was not the mother. A normal DNA test proving a mother-child link would show a 50% match between their DNA patterns. Yet Lydia's DNA showed no match at all.

And here she is to tell her extraordinary story: 

The twin within (4) A chimera

What is a chimera? 

A person who is a chimera is made up of cells from different people. So some of their cells have the DNA of one person and the other cells have the DNA of another person. How do you do that?

Imagine that inside of a womb, instead of there being only one egg, there are actually two. If both of these eggs get fertilized by two different sperm cells, you get fraternal twins. Fraternal twins are no more related than any brother or sister.

Now, imagine that instead of developing separately, these fertilized eggs actually fuse. Then only one baby would develop. This baby would have cells from not one, but two different zygotes.

Remember, every zygote carries its own unique set of DNA. So the baby would have two different sets of DNA-this baby would be a chimera. 


IF you have ever had a transplant you are a chimera, because you have cells of different  genetic makeup sharing your body.  Even a blood transfusion will makes you a chimera for a few weeks, until the blood cells die.

Does the presence of cells of another human in your body make any difference? I hear you ask. Well, it does.

Microchimerism, that is the presence of a very few cells from another human remaining within the body, is common  in women after pregnancy.  ( see article here)
Autoimmune diseases are thought of as disorders in which a body's cells inexplicably attack its own normal tissues.


The physical consequences are that your immune system will attack your own body - at least the individual cells of your body that are "foreign" because of the differing DNA.


The psychological effects are more subtle: a sense of being more than one person, as indeed you are.  For a woman after pregnancy, a sense of being forever bonded to her children, living and dead, as if they were still within her. As a mother myself,  I feel a strong blood bond with my children, now both far away, and even the one I miscarried at 3 months of pregnancy 37 years ago. Perhaps it is possible to feel a sense of bonding and connection to the cells of another person within your body.  If the DNA is not so very different ( a fraternal twin sibling does share half your DNA)  then perhaos your body can learn to tolerate this " foreign body". If not, then perhaps that is the basis of the idea of the "evil twin" who may have become part of your personality.

I have heard of womb twin survivors who have two very different ways of being themselves, and they switch from one to the other almost unconsciously. In one case I regularly visited a woman suffering with autoimmune disease  (MS) over five years.  She was sometimes sweet and rather pathetic and sad but at others aggressive and raging. Two people in one. Was she a chimera I wonder?