Twinendipity & Science

I’ve been thinking about writing a post about twins for a few weeks, after all that’s what Multiple Musings are supposed to be about.   I’ve been off on a “me” track for awhile.  Today I had two serendipitous signs that it is time for this post.

I received an email from Gail, former Chair of Multiple Births Canada, an active member of Temiskaming Multiple Births.  She sent me the slides for a presentation by Dr. Fiona Bamforth.  Dr. Bamforth studies twins and does zygosity testing.  She presented at the 2010 MBC Conference in Edmonton.  Based on the slides I’d say the presentation must have been fascinating. 

The other serendipitous event was while baking muffins.  I cracked an egg, double yolk!  I cracked another egg, also double yolk!  Totally a sign that I had to write about twins, don’t you think?

Back to the presentation.  It was on types of twinning, the possible causes of twinning, zygosity and zygosity testing.  This stuff fascinates and excites me (intellectually – just to be clear).  It makes me really want to get involved at the national and international level.  It also makes me think about my girls and the implications.

Here I will focus on the possible causes of twinning in mono-zygotic twins.  Hopefully I get this right, I really need the “Twins for Dummies” version, but all I can find are scientific papers.  I’m no medical doctor,and I dropped out of Latin in grade 11 so I had to google a lot of concepts and words!

First of all the causes of monozygotic twinning are heterogeneous, which I think means there are many possible reasons, most of them not understood, and largely still in the “theory” stage.    There are genetic and environmental causes.
In this post I will focus on one genetic theory:  Non-random x-chromosome inactivation.  WTF you say?  So did I so I did a little research. 

I learned a lot about random x-chromosome inactivation.  All females have two sets of x-chromosomes; one from mom, one from dad.  One set for each gene is turned off, and the process that turns some on and others off is random.  That may be why some mono-zygotic twins aren’t identical in appearance.  This can also explain why one mono-zygotic twin may get a certain inheritable disease while the other doesn’t (there are many recessive genes linked to the x-chromosome and the gene isn’t turned on in both twins).  OK, I get that.  But what is this non-random stuff? 

I think that the idea is that in the initial random inactivation, two clusters of cells arise with opposite inactivation patterns.  These clusters then repel each other and cause the embryo to split, therefore causing the mono-zygotic twinning.  There is some evidence to support this but there is also evidence to refute it.  (There is more to this, chorionicity likely plays a large role,
mono-chorionic twins share a placenta and there are often connections
between the cords, all this adds to the magic and confusion). 

Was this the cause of Fiona & Sophie’s split?  Obviously I’ll never know, but it is very interesting.  I’m more prone to think it was because the clinic fiddled with the zona pellucida (they poked a microscopic hole in the microscopic shell, it’s called assisted hatching) but who knows.

I watch my girls and am amazed by them daily, they have such a close
bond.  They also fight so I question how different are they from other
siblings who also have a close bond and fight sometimes.  Regardless of
their zygosity 

Dr. Bamforth is offering the test with a cheek swab at a very
reasonable price for members of Multiple Births Canada (while funding
still exists).

One may wonder; why is this important?  Should we test zygosity (DNA test to find out if twins are di-zygotic  or mono-zygotic)?.  I’m still thinking about this and wishing I had been at that presentation so I could have asked Dr. Bamforth.  I’m curious what other twin parents think, should you get your twins tested?  Why or why not?

Check out this progression: