[tri-med] Re: Mistakes in Diagnosis

----- Original Message ----- 
From: "Karen"
> There are a lot of "full" T-18'ers out there that don't "fit" the doctors
mould for what they expect of a T-18'er, and so mosaicism is or has been
suspected. There are a lot on the list who have gone for the check and
double checks. (anyone going to confess to Debbie :-))) but I don't know
anyone in who it has been formally confirmed.

I probably should clarify this before I go and do some work (otherwise I
will be in big trouble :-))
I am aware of a couple of "full" T-18'ers who have had FISH studies done in
addition to the regular g-banding. G-Banding showed "full" T-18, but the
FISH studies indicated that they could have been mosaic. However in both of
these kids the percentage of "typical" cells were small (less than 10%) and
have been officially but down to artifact.

All FISH test results MUST be confirmed by g-banding, and if there is a
discrepancy the g-banding stays as the "official" result.

To explain artifact in FISH testing. Most of you know that with FISH testing
they put a specific probe into the sample, this attaches to all the targeted
chromosomes (I will use 18 as an example). Once attached it makes the 18th
chromosome "glow in the dark". Once the chromosomes "glow" they physically
count the glowing chromosomes. Sometimes however before they can finish this
counting the "glow" fades (poor signal or else they just took too long to
count). This is called artifact. Anything less than 5% of "missing" glows is
considered "normal" but some labs will discard anything less than 10% (there
is no universal rule). Between 5 and 10% they will usually request a
re-test.

However no matter what the count in a FISH, g-banding always remains the
official result - if it can't be re-produced in g-banding it doesn't
officially count. To run the best chance of detecting mosaicism in g-bandin
they should test a minimum of 100 cells. Most labs test somewhere between 5
and 20. IMHO 5 is not enough and 20 is marginal.

With the two "full" t-18'ers that had mosaic FISH results, one had a 5%
count - officially ruled as artifact, the other had 7% - so the jury was
still out. In both cases g-banding said "full" T-18 - so thats the official
diagnosis. Unfortunately though there can be no re-test as both children
have since passed away.

The roots of true achievement lie in the will to become the best that you
can become.
-- Harold Taylor

Keep Looking For Rainbows!!
Karen, Mum to Alex (8 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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