[tri-med] Re: testing of cells results

----- Original Message -----
From: "Aaron & Sandi"
> My question is does this mean the other 18% of cells are normal??? and do
not contain an extra 18

You can ask almost anything here and someone will have some experience, but
you really need to speak with your geneticist as well. I can give you some
answers, and lots of questions for your geneticist.

The answer is maybe this is a case of mosaicism for trisomy 18 and probably
not for the sex. What you really need to find out though is what the
g-banding or cultured results show.

The result that you have given is the result of a FISH test (maybe a SKYE
but I would guess a FISH). Although they are widely used these days they are
still considered either experimental or at risk of innacuracy and so any
results from a FISH test must be confirmed with a cultured karyotype. I will
explain why in a minute.

The cultured karyotype ALWAYS takes precedence over the FISH. So if the
cultured karyotype says 100% of cells showed T-18 they will consider the
result full T-18. If the cultured cells showed even 1 "normal" cell they
will consider it mosaicism.

They may redo the test, and they may suggest other testing to confirm the
results, eg if this prenatal they can either redo the amnio, do a PUBS (or
cordocentesis - very high risk to the baby though). If this is after birth
they may repeat the blood test and suggest a skin biopsy.

With the results that you have there are a lot more questions I would need
to know to give any real answers, and these are probably best answered by
your geneticist anyway. (For example what sort of probe was used, how many
cells were studied, what medium was studied, how many flasks etc) But in
general terms

99% of the cells showing both an X and Y chromsome is pretty much definitive
that the baby is a boy - 1% not showing both X and Y is simply statistical
variation. The signal in the cell or cells not showing both the X and Y
probably just "faded" very quickly.

20% of the cells not showing an additional 18th chromosome is not so clear
cut. It may be statistical variation it may be mosaicism.

Personally I would be leaning towards mosaicism.

If it were me I would be asking for a repeat test to confirm either way
(depending on risk factors and your own personal feelings) and I would
definitely not be judging anything about this baby except the babies exact
medical status.

My own personal experience (that is talking to lots of other mums with a
prenatal diagnosis of mosaicism) tells me that mosaicism percentages via
amnio are usually higher than after birth. eg IF (big IF here) this IS
mosaicism and its 80% in an amnio then the number of T-18 cells detected
after birth, in blood will be much less. I would guess somewhere around 50%.

Percentage of course does not mean that the baby will not have problems,
statistics on survival with mosaicism are really not much better than with
"full" T-18 and that life wont be hard. But it does mean that its easier to
argue with the doctors about quality of life and the prognosis
developmentally is usually "better".

Although we like to think of cytogenetic tests as being is infallible this
is not the case. Doctors can and do make mistakes. Test results are not
always 100% accurate.

With a FISH test the chromosomes are prepared and then painted with a
"paint". A probe is then added to the cells that matches to the cells that
they are testing for - in this case 18th chromosomes. The probe ONLY picks
up signals from the chromosome, or part of the chromosome that it is meant
to. For example an 18th chromosome probe will not show you that there is an
extra 17th chromosome (or missing 17th chromosome). This is why the doctors
MUST know what they are looking for.

There is a rapid test FISH probe that is done. It detects 18, 13, 21 and X
chromosome problems - but this is fairly new and still only looks
specifically at these chromosomes no other. (each chromosome comes up in a
different colour - very pretty)

A FISH probe cannot show you if the signal is part of a chromosome and other
finer detail. This is one reason why it must always be confirmed by a
cultured karyotype. So for example a FISH test will not show you if the
problem is a partial trisomy 18 unless they are looking for a very specific
break point, but thats a different type of probe all together.

The glowing light that they read to count may not "take" to a few cells and
it also fades fairly quickly, this is the usual reason why FISH tests will
show a false mosaicism result. Under normal circumstances you would expect
any sample to lose the signal from a few cells, as with the X and Y. This is
statistical margin of error.

Losing 20% or there abouts of signals (especially when you only lost 1% off
the sex cells) is getting a little high. It may be statistical variation -
it may be true mosaicism. You will need to discuss this with your doctor and
the lab as to what they accept as statistical error. There are NO universal
standards for this, each lab makes their own rules.

Also what you were told by the doctor can depend on what sort of doctor told
you. Obstetricians for example often have little or no knowledge on the ins
and outs of genetics. Many wouldnt know the difference between full, mosaic
or partial if it turned around and bit them!!!!

This signal is seen as a pretty coloured glowing light. The doctor must then
manually count how many signals that they see - in this case 82% of the
cells that they looked at had 3 signals instead of two from an 18th
chromosome.

There was another family on the list (HI!!!) for whom I had this discussion
with my favourite and world respected cytogeneticist (a cytogeneticist is
the person who literally does the chromosome test). She was happy to accept
up to 5% as a margin of error in most cases (in 500 cells), but would still
report it. However she didnt like the standards for the lab I was asking her
to give a second opinion on. She would give them at least 10% probably
higher on the margin of error before asking for a retest. Additionally the
cultured karyotype showed full trisomy 18 (only 20 cells).

The second opinion verdict, even though the FISH showed mosaicism of 11%
(that is 11% of cells had a normal 18th chromosome signal) that we needed to
consider that the child had full T-18. Retest was not possible as the child
had passed away.

Now that is probably a longer and more complicated answer than you were
asking for - sorry. And I noticed after glancing at a few mails that we now
have a resident lab person on board that may give us both some better
insight.

But the bottom line from where I am sitting is that yes this may be a case
of mosaism but it may not be.
If you have the results I would love to know - what the medium was that they
tested (eg is this blood or amnio). How many cells did they test? (eg 5, 20,
100, 500) How many flasks did they test? (eg if they tested more than one
batch of cells from the same sample - this equates with something called
mosaicism grade)

And of course what were the results of the cultured karyotype? How many
cells did they sample? Were the cells that they tested fragile? or different
in anyway?

BTW cultured karyotypes can also be wrong - ask Alex about that one. His
original test after birth showed 100% normal cells - second test showed 60%
of cells with an extra 18th chromosome. Third test showed 80% of cells with
an extra 18th chromosome. FISH test on skin showed no cells with an extra
18th chromosome but we havent repeated that one, it hurts and leaves a
scar..........

When people ask me, a mother with experience of mosaicism and who went
through the wrong result route, and also as someone who has spoken with lots
of cytogeneticists and geneticists about mosaicism but who is NOT a doctor.
I always recommend that families ask for a minimum of 100 cells to be tested
by a regular cultured karyotype from at least 2 different flasks. With FISH
testing I recommend that they screen at least 500 cells at a reputable lab.

If there is any doubt about the test results I would always go with the
"better" result (better than going with the wrong result) until it is proven
otherwise. Remember you also have the right to ask for the test to be
redone. I have seen way to many errors in genetic tests to be comfortable
with just accepting that these tests are 100% reliable. They are most of the
time - please dont get me wrong, but there are so many factors involved and
they can and do make mistakes.

I guess in some ways I have never gotten over the fact that a mum here in
Australia had an amnio that showed T-13. Like the vast majority of people
she went ahead and interrupted the pregnancy. Unfortunately the autopsy
showed no physical signs of T-13 and neither did the culture done at the
autopsy.......................

Man must not allow the clock and the calendar to blind him to the fact that
each moment of his life is a miracle and a mystery.
- H. G. Wells

Keep Looking for Rainbows!!!
Karen, Mum to Alex (7, T-18 mosaic)
Sydney, Australia
http://members.optushome.com.au/karens
http://www.trisomyonline.org

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

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