[tri-med] Re: Baby news

----- Original Message ----- 
From: "Fawna"
> >i am still having a hard time understanding the balanced and  unbalanced
>>part of this i am not sure what julian is.  that's something i  need to 
>>ask
>>the genetics team about.from the way it was described to me here my
>>"guess" would be that he is balanced, but not sure.
>

> Forget balanced or unbalanced translocations.  Julian would be neither,
> because he's mosaic.  Mosaic ALWAYS develops after conception, whereas
> an inherited translocation causes either an uneffected trisomy carrier
> (balanced) or an effected (unbalanced) trisomy in every cell of the body
> (non mosaic).

I am with Fawna on this although I know Michelle will have posted the 
alternate theory which although possible has essentially been discounted 
over recent years.

What has happened Sarah is that sometime after the first few hours or days 
of conception, when the cells were dividing one of the chromosomes, in your 
grandsons case the small p arm of the 1st chromosome broke off and ended up 
in the other half of the division.

So to simplify that greatly you have:
sperm meets egg and the cells start dividing
One cell that divides into two. These two cells divide and become 4 and so 
on.

In the cells the chromosomes duplicate and then one half migrate to each end 
of the cell - in this migration one of these very fine strands of the 1st 
chromosome lost a piece, it stuck to another chromosome and went to the 
wrong end of the cell to which it belonged.

When that cell continued dividing it just kept dividing with the additional 
piece. (the cell that ended up with the missing piece would have been 
discarded by the body as a polar body - but thats getting technical, I just 
want you to know that there probably arent some cells wandering around in 
his body that have a piece missing.) Deletions as a generalisation are 
usually much more "fatal" to the developing baby than a trisomy.

The other cell whose chromosomes didnt have the broken piece in it just kept 
dividing normally - so you end up with what they call two lines - the 
"normal" cell line which has all the typical number and structure of 
chromosomes and the second line which has the additional piece. Thats 
mosaicism.

Exactly when mosaicism occurs and how much of an anomaly there is will 
determine exactly how the child will develop - and thats something that only 
time will tell. All I can tell you is that it happened after the very first 
cell divided and before the 4th month. Its also feasible that it can happen 
even after birth but that gives you a different picture totally from what we 
see in our children.

So in short mosaicism CANNOT be inherited from either parent - its just not 
possible. Mosaicism is one definite way of absolving either parent of 
"causing" the problem. It also means that the risk of it happening again are 
so remote its not even worth thinking about.

List folk are probably familiar with the fact that sometimes I refer to Alex 
as being one in a million - but thats because statistically he is.

Someone who is better than me at math might want to recalculate this 
but..........
Taking the better stats - One in 5,000 children will have trisomy 18 (0.02% 
of all births)
1% of those children will have mosaicism.
So the chances of Alex developing mosaicism were 0.0002% or literally one in 
a 200,000. For me to have another child with mosaic trsiomy 18 are literally 
one in a million. Trisomy 1p mosaicism would be even rarer still, it just 
makes him super special.

"We come to love not by finding a perfect person, but by learning to see an 
imperfect person perfectly"
Sam Keen

Keep Looking For Rainbows!!
   _--_|\
 /Karen \
 \ _.--._ /
          v Karen, Mum to Alex (10 years, T-18 Mosaic)
http://members.optushome.com.au/karens


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

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