[tri-med] BRENDA~Genetics 103 - Recurrence Risks

Another repost that I thought you might find useful.
Michelle mom to Alex (15,partial trisomy 14 mosaic) and Molly (12)
MichiganUSA

> This is a cut and paste of two posts - the first part refers to the risk
of
> recurrence in Trisomy 18 (full) and the second part the risks associated
> with translocations. I will send a separate post with more detailed
> information about risk based on age.

> In general the chances of a trisomy occurring again are less than 1% over
> the rest of the population based on age and excluding translocation. So I
am
> not sure what you mean sweet by increasing so greatly???
>
> In general the risk of any problem happening during a pregnancy for any
> person is 2% - 3%, that is 2 to 3 out of every hundred pregnancies will
> result in some sort of congenital abnormality eg spina bifida, chromosomal
> abnormality, club foot, heart defect etc etc etc.
>
> Once you have had a child with a chromosomal abnormality (that is not
> related to a balanced translocation!!) that risk only increases by less
than
> 1%. But like everyone else you still have that other 2 -3% chance. I guess
> thats what seems so unfair about this whole funpark!!! I think that
dealing
> with Trisomy is enough - why do we need all the other "normal" worries as
> well!!!!!!
>
> The risk based on age however increases far more rapidly. Now why that is
> again no-one is really sure. What we do know is that the age related curve
> for Trisomy is a three hump curve :-)
> There is a small increase (quite small) for chromsomal abnormalities in
> teens, then it sort of levels out until age 35 where it climbs again
fairly
> sharply.
> As I said why they don't know. Is there something in hormone production
> during the "peak" reproductive years that helps a healthy mother "get rid
> off" "abnormal" embryos through spontaneous miscarriage? Is this the age
> that "healthy" eggs are released and the less "perfect" ones are left to
> later?? Is it because the mother is healthy that some are able to carry
> these babies to term?? Sorry no-one really has the answers as yet and
> because of the nature of the research that would be needed to find out we
> are unlikely to get any real answers.

~~~~~~~~~This part applies the most to you Brenda.
> From: <pjvictor@xxxxxxxxxxxxx>
> > She told me that if Nicholas were a carrier that his
> > chances of having a child (ie: miscarriage,
> > stillborn, trisomy 13, or another carrier) would
> > fall in the 10% catagory. I asked why this figure
> > was so significantly less


> OK Penny and Joe,
> I thought I knew this answer and then Penny's answer threw me soooooo I
> asked a genetic counsellor :-))
>
> Here goes!!!
> There are two types of translocations - reciprocal and Robertsonian.
> Now given the situation where this is an existing family condition so that
> there is no mosaicism involved then every sperm would carry the
> translocation in both cases.
>
> So in the case of a reciprocal translocation there are 4 possibilities for
a
> fertilised egg
> Normal chromosomes
> Balanced translocation
> Unbalanced plus some extra chromosome
> Unbalanced minus some chromosome
>
> so the theoretical chance (and I emphasise theoretical!!!! - read to the
> end) is a 50/50 chance of there being something wrong.
>
> Now in a Robertsonian translocation there are six possibilities (I will
use
> the example of an 18/13 translocation)
> Normal
> Balanced
> Unbalanced with an extra 18
> Unbalanced minus an 18
> Unbalanced with an extra 13
> Unbalanced minus a 13
>
> So theoretically the risks are higher however a monosomy 13 and a monosomy
> 18 are "incompatible with life" and will result in a miscarriage (possibly
> just a "late" period). So the chances are 2 to 1 of something going wrong.
>
> HOWEVER
> every situation is different!!!! and anyone with a translocation should go
> armed with their karyotype and talk specifics with a genetic counsellor.
> This is a very brief THEORETICAL overview!!!! (I spent an hour listening
to
> the variations!!! chances of partials, "normal" risks added in etc etc.)
>
> The other be wary thing is that males who are carriers of a translocation
> have babies with problems less often than women but they HAVE NO IDEA
WHY!!!
> Its an observation of the population not something that can be explained
by
> science. (But can science ever explain anything fully?????)
>
> Now one other titbit of information is that because sperm are totally
> replaced every three months or so age continues to play no factor in
> increased risk with males. They use the same template all their lives and
> unless there is an environmental effect on that template they will produce
> "mistakes" at the same rate all their lives.
> It is only women who suffer the increased risks due to age and the
splitting
> of the egg at ovulation.
> So sperm and eggs make the same number of "mistakes" up until age 35 when
> the risk increases for the eggs but not the sperm.
>
> I hope that helps :-)) and doesn't scare anyone, remember this is all
theory
> we all know that reality is very different!!!!
>
> Take Care and Keep Looking for Rainbows!!!
> Karen, mum to Alex (5, T-18 mosaic)
>



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