[tri-med] Re: Amnio Issues

----- Original Message ----- 
From: "courtney holihen"

>I know of another baby with trisomy 13 mosaic who had a false positive with 
>the amnio.  His blood came back negitive for Trisomy 13 mosaicism and they 
>are awaiting results for the skin tests.  www.samuelsspace.com  They are 
>also trying to figure out how and so far the conclusion has been that 
>sometimes miracles do happen.>>

No this is VERY possible in mosaicism, we have seen it happen a few times on 
the list, including my Alex. The amnio is actually correct and so is the 
blood test. What typically happens is that the amniocentesis detects the 
trisomy accurately. Now remember that an amniocentesis tests amniocytes 
which are primarily made up of skin cells. In fact its not until after 23 
weeks that any gut cells are included in amnion as its not until then that 
the baby starts swallowing and urinating amnion to collect gut cells in the 
amnion. So an amniocentesis is probably measuring skin not blood.

However when the baby is born the trisomy is confirmed via a blood test 
which tests peripheral lymphocytes. These are NOT the same cells tested 
during an amniocentesis.

So when the blood test comes back as "normal" after birth that does NOT mean 
that the baby does not have a trisomy, rather it most probably means that 
the baby has tissue specific mosaicism.

Will the skin test come back as positive for a trisomy? Maybe, maybe not. 
Remember that all karyotypes are taken from random samples and the results 
can be different depending on which spot of skin they test. My Alex is a 
typical example. John Carey himself took a skin biopsy from his left butt, 
600 cells were FISH'ed and all came back as normal. Recently another skin 
biopsy was taken from near his navel (almost the same level as the butt 
biopsy just from the front) and it came back as 30% trisomic cells (400 
cells FISH'ed). Alex's blood test results come back at between 66% - 84% 
trisomic cells. The reason for the difference is Blenko's lines. Even though 
the samples came from a straight horizontal line or the same dermatome strip 
skin actually forms in utero in Blenko's lines which are more swirls than 
straight lines. Two skin samples taken half an inch apart could render 
totally different results.

I have to get back to Alex (he is really very ill and sadly appears to be 
failing way too fast), but perhaps Michelle W will tell the tale of Lena. 
Lena also had the same thing happen - small percentage of trisomic cells 
found in an amnio, it was confirmed via cordocentesis (the only way to test 
a baby's blood before birth). After birth the blood test showed zilch as did 
the skin biopsy. They took another biopsy on her first birthday and the 
trisomy finally showed up..........

I feel sorry for the parents who have been told that this is a miracle and 
haven't had all this explained to them. While its not a common occurance, 
its certainly not unheard of either. Any geneticist worth his salt would be 
aware of the possibility and should have explained whats likely to happen. 
How devestated they could feel when the skin biopsy comes back or worse how 
confused they may be if the baby has developmental delays. Skin is formed 
from the same layer as brain tissue develops from and so is probably a 
better indication of cognitive development. (note I say indication - nothing 
is certain in mosaicism). Blood on the other hand is a better indication of 
physical problems as most of the organs are formed from the same cells as 
blood. Thats why the experts feel that Alex has many of the medical problems 
of trisomy and few of the cognitive.

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

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