Chimera Twins...science gets me thinking

Today I read a post from @grottbags and how connected she can be to her brother @mobbs and a couple of things in that post had me thinking back to the times before my children were born, the time I was carrying them and the life that has existed since then. The fact that one is quiet, one is loud; one is fair hair/fairskinned, the other dark; one is quick tempered the other slow to anger, and the similarities; tall, blue/green eyes, passionate, strong willed... two peas from the same pod, as are all children of same parents. That lead me to thinking about something I'd read a while ago about a genetic mix up resulting in Chimeras.

I had 3 pregnancies in all. The first was a disaster and ended too early for the babies to survive. I had a miscarriage - one on a Monday, followed by another on the Friday. I didn’t understand it all at the time. The scan on Tuesday after I lost ‘the baby’ showed a sac and no baby, still in situ, but the tests said I was still pregnant so they hospital had me on bed-rest – just in case they were wrong. Years later I found out that whilst there was no ‘viable’ child I had in fact got pregnant with twins. The first bleed had led to one being miscarried. At 13 weeks they could sex it and it was a boy. The empty sac in the scan days later was a remnant of one that had developed no further than first stage. Obviously, neither were meant to be on this earth.
When I carried my daughter again we had a twins scare as the GP said he could hear two heartbeats. I listened, so could I. I went for a scan. One baby. Odd! Once the delivery was over I saw a note on my file which I read as “2 succinct lobes”. I asked what it meant and the midwife brushed over it saying it was just a description of the placenta for the doctors.
When I had my son, we had the same two-heartbeat syndrome and one baby but after delivery the same note appeared on his birth card. Again, I asked and again was told ‘nothing to worry about’.
Being who I am I did some research. The actual term is ‘Succenturiate lobe’. meaning extra, almost separate. The 'lobe' was still part of the one placenta. Too separate and it would have been two placentas and a definite twin pregnancy. A Succenturiate lobe can be just where the placenta grew a bit funny and developed an extra lobe as opposed to being a standard disc shape. It can also mean that there was another baby at the very early stage that became non-viable. A twin. I wondered if the 2nd heartbeat in each pregnancy was in fact a twin that died. It’s possible as the body has a way reabsorbing anything that wasn’t quite right just as equally as it can eject one in the form of a miscarriage.
Now, I have assumed that all three of my pregnancies possibly began in twin form. This was kind of confirmed when I went for fertility treatment years later (different story) and a scan at the request of the infamous Professor Winston (of IVF fame) showed both ovaries erupting an ‘egg’ at the same time BEFORE I had begun the treatment (yeah fertile as you can get!). I even have a scan photo in a box somewhere. This is not my ovary – but a very similar picture

Had I been able to get pregnant at that point in the normal fashion it quite possibly would have started as a twin pregnancy again. I had twin uncles on my dad's side, twin great aunts on my mother's and have twin 2nd cousins, so there is something in the genetics of my family.

Now, what has this got to do with the title. Well it’s the background to why I was looking up CHIMERA today. I am not saying my two are by the way. It’s quite unlikely. I’m simply fascinated by biology and the way life deals with its own creation problems and in some ways creates something more interesting – if that can be so. In my case my twin child was absorbed by me to the point of non-existence but it could have been the other alternative. Chimera children.

So what is a CHIMERA? In layman terms it is when, in animals/humans there was a twin (or multi birth) pregnancy but one of the zygotes – before they get going into proper development – absorbs another (sounds horrific but it’s not).
So, in this example post I refer to fraternal twins, when two eggs become one. This can’t happen with identical twin pregnancies because identical twins split from one egg. There’s no time to split and reabsorb before the development gets too far. However, with fraternal twins, two separate eggs are fertilised in one pregnancy. If they reach the womb and hook in to start pregnancy-proper it can happen that one absorbs the other, or one is absorbed into the placenta and the genetic coding is taken up by the remaining one at the earliest stages, before cells go to start their designated job. As far as I can find, there’s no definite reason for this other than perhaps one is stronger, or it’s simply the close proximity of the eggs at this stage (zygotes). The result of this absorption will create Chimera being. A person or animal that has two differing and distinct DNA sets. (It can also happen with seed of plants).
Now, reading more into this I found that it’s so much more fascinating that I originally thought, although fascinating enough. It turns out that chimera people and animals can be obviously so like in these photos where it is obvious that the body is two in one. This is not Siamese/conjoined. This is two different gene sets working together in one normally healthy body.

It can also be very non-conspicuous and I was astounded to read that there may be more chimera than we’ll ever know due to the inability to completely test people, or the fact that people are so unaware that tests are never requested. I was blown away to find that some chimera can have genetic coding in blood that differs from the coding in skin cells or have the same blood and skin but different coding in organs.
Some chimera may have different colour eyes – but this can also be caused by other conditions. More rarely but more distinct is 2 colours in one eye. We all have tones, which is obvious in anyone with blue/blue green and grey eyes but in chimera there are distinct patches rather than tones.

Hair colour or a patch of curly in otherwise straight hair can be a sign of being a chimera. As with animals a true chimera human may have a natural patch of different coloured hair, but again this can be caused by other issues. The only way to know for certain is genetic testing. One chimeric sign in humans is a skin condition where both genetic codes for the skin causing slightly different skin types. Under UV light a person looks like they have tiger stripes. It causes no issue and cannot be changed.

Most chimera people will never know, but on occasion it comes to the forefront.
Like when Karen needed a kidney transplant and found out – by eventual genetic testing – that her ovaries or at least part of them were in fact her twin sister’s, which meant that two of her three children weren’t a full genetic match (read from link below). Or when a couple were going to sue a fertility clinic because their new born child’s blood did not match the father’s only to eventually find that he was a chimera and his sperm cells were in fact his absorbed twin brothers’ cells.

So maybe these twin pregnancies I have had could have lead to chimera children. But they didn’t. It’s a fascination but not a requirement. They are who they are, and nothing will change that. My babies are simply that, just an ordinary brother and sister, two people who compliment each other so well, are opposites of the same coin and it’s a blessing that I created life twice.
If you’re interested in reading more have a look here.

I read this
and this
and this
and this

and more...and simply got more and more intrigued… and unnerved as now science are making chimera – human animal hybrid embryos. Mother Nature may get hiccups at times, but should we really be hiccupping for her? That’s a whole new post in the making.