[tri-med] Calling all mosaic-ers

This past week I have been studying intensely most of the literature 
available on mosaicism. My focus has been on the really recent developments, 
that is, within the last 6 years.

I have found some quite interesting material and am happy to do some OCR 
work on the articles for people - but with 22 chromosomes out there I need 
to know who wants what "flavours". I will automatically do 13, 18, 14 and 8. 
Any others? There is one article in particular thats quite brilliant - but 
unfortunately its very very technical and 41 pages long. If you want it in 
its entirety then you may need to sit there with a dictionary to read it. 
:-))))

Also I know that we have a few folk with Trisomy 14 variants. For those that 
haven't seen a geneticist recently you may want to ask about DNA analysis as 
they have found that paternal UPD for chromosome 14 may result in gene 
imprinting. OK OK OK I know that some folk are going to ask what is UPD and 
why is that important? So here is a basic explanation. Stolen from MedGen's 
web site :-) (Thanks Wendy!!)

"In 1980 Engel introduced the concept of uniparental disomy (UPD). 
Uniparental disomy (UPD) arises when an individual inherits two copies of a 
chromosome pair from one parent and no copy from the other parent. Recall 
that normally a baby inherits one copy of each chromosome from his/her 
mother and one copy of each chromosome from his/ her father. In the rare 
circumstance of UPD a baby may have two copies of one of his/ her mother’s 
chromosome and no copies of that chromosome from his/ her father.  This is 
called maternal UPD.  Paternal UPD is when a child inherits two copies of a 
specific chromosome from his/ her father and no copies of that chromosome 
from his/ her mother.
This abnormality in inheritance may lead to health concerns in a child.  UPD 
can result in rare recessive disorders, or developmental problems due to the 
effects of imprinting.>>

Of course it may have no effect, especially in some chromosomes. But they 
have confirmed that it is a factor in Trisomy 14. Essentially paternal UPD 
can allow two recessive genes to activate. For example think of cystic 
fibrosis. One parent can be a carrier of the gene for cystic fibrosis but it 
will not "activate" unless they have a child with a partner who also has the 
gene. What happens with UPD is that the parent has the recessive gene, but 
because the baby has two chromosomes from the parent that has the recessive 
gene it does activate and can cause problems.

UPD isn't an issue if the flavour (number) doesn't have any recessive genes. 
eg the 18th chromosome doesn't have any recessive genes (that we are aware 
of) so if you inherit two from one parent then it causes no problems. But 
they have found that there are recessive genes on a few chromosomes - 7, 11, 
14, 15 and especially 2 and 16. (I knew that 2, 11 and 16 were problems but 
I wasn't aware of 7 and 14. In 14 it is only a problem if they have two 
chromsomes from the father - if its two maternal 14 chromosomes its not a 
problem. Unfortunately you can't tell which without doing a DNA analysis.

UPD is more of a problem with mosaic trisomies, because there is the risk of 
there being trisomic rescue. Brief explanation - the baby starts out as a 
"full" trisomy but there is an attempt to rescue the cells from the trisomy, 
and so the cells lose one chromosome. In a trisomy there is always a UPD 
somewhere, that is one parent gives one chromosome and the other gives two. 
However when the cells start the rescue they may end up losing the single 
chromosome and leaving two from the one parent. Without the other parents 
gene to suppress the other two it results in gene imprinting. It certainly 
explains why there are such great differences in the same mosaicism 
flavours.

So it may well not be an issue, but its definitely worth bringing up with 
your geneticist.

Life consists not in holding good cards but in playing those you hold well.
                                            -- Josh Billings
Keep Looking For Rainbows!!
   _--_|\
 /Karen \
 \ _.--._ /
          v Karen, Mum to Alex (11 years, T-18 Mosaic)
http://members.optushome.com.au/karens 

                  Building ___ooOOoo__ Rainbows
                       www.trisomyonline.org
                  Families Helping Families On-line

Other related posts: