[tri-med] Re: Karen--grandma to Julian : Genetics 103 - Recurrence Risks

>PLEASE HELP AND TELL ME IF THIS IS RIGHT.   And what are
>the odds of her having another baby with trisomy??? My
>grandson's geneticist told my daughter that what
>Julian has was not passed on by her or his father. Can
>he know this without having tested the parents??

Hi Karen,

I'm not sure if you would have picked up on the most important
part of list mum Karen's "Genetics 103" e-mail as it relates to
your specific case, so let me point it out to you....


> 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....

> HOWEVER every situation is different!!!! and anyone with a translocation
> should go armed with their karyotype and talk specifics with a genetic
> counselor.

Point being that your concern IS with a case involving mosaicism (PT1m),
so therefore it is virtually impossible that it was passed on from a
translocation carrier.  If in fact it was inherited, then it would have
had to start out as a non-mosaic case, that then later developed a
mosaic normal line.  Odds of that being extremely miniscule.

And the only other way ever documented (again like one case ever) was
a parent who was unknowingly mosaic them self, who then had a non-mosaic
trisomy child.  Reason being is that there are only 2 lines involved
here.  One with no trisomy, and the other with a full blow whatever
chromosome (or part of it) that the parent was mosaic for.  You just
can't pass on what you don't have yourself.  So here again, in order to
end up with a mosaic child from a mosaic parent, it would involve
starting as a non-mosaic case that later developed a normal cell line.
Which brings us right back to an even more miniscule possibility.

Odds being what they are all around, I would agree with her genetist
that Julian DIDN'T inherit his trisomy from a parent, and therefore I
wouldn't risk the amnio myself, but that's just me....

Fawna, mom to Philina 22yrs (PT6p & Moya Moya)
Research coordinator for  the  TRIS Project
http://home.mindspring.com/~fawna33/



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

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