Re: Down Syndrome and Radiation Exposure

[Rebecca Hollis <rvhollis@lanl.gov>]

I have a child with Down Syndrome and after her birth I met with
geneticists about this issue.  I was told that the factors that are
responsible for Down Syndrome are not known, but studies investigating
chemical and radiological exposure have found no correlation between
incidence and exposure.

I would recommend that you have the person with this concern speak with a
geneticist.  This is a pretty common condition and terotogenic exposure is
also a very common concern that I think most geneticists address
regularily.  Talking to a geneticist may also be reassuring to the person
since it will be someone outside of the rad community saying there is no
link.

Also, FYI there are several different "types" of Down Syndrome. In only one
of the "types" does the genetic defect occur in the early stages of
embryotic development.  This is know as mosaicism, and often results in
less severe symptoms.  This form is rare, I think less than 1%.  All other
forms, occur prior to fertilization, and result from incorrect splitting of
the 21st chromosome in the production of egg or sperm cells.  So if the
person is concerned about prenatal exposure, more than likely the extra
chromosome appeared on the scene before pregnancy and may not have even
come from the mother.

As to Zack Clayton's question about age affecting the ability to
spontaneously abort fetuses I don't know the answer to your question but
the geneticist we met with told us about a study that showed a correlation
with increased paternal age as well as maternal age (fathers have to be
much older than mothers to have an increased risk however). I also know
that very young mother's (I think it's 16 and under) are not the lowest
risk category for incidence of DS.  So it appears there is a slight chance
at young ages then it goes down until sometime in a mother's 20's (?-I not
sure on actual ages) and then begins increasing again but much more
steeply.  There may be two different factors working here however, because
there is a higher chance of one of the less common "types" for very young
mothers. I'll see if I can find these citations.

I wonder if there may be some hormonal-linked selection process that
discriminates against eggs or sperm with the anomaly.  That may account for
age issues, difference in incidence from mothers and fathers, etc.
**************************************************************************
Rebecca V. Hollis, Ph.D.                        phone:  (505) 667-1631
Radiation Safety Training Team Leader		        fax:    (505)665-4859
ESH-13, ES&H Training   MS J596                 e-mail: rvhollis@lanl.gov
Los Alamos National Laboratory
Los Alamos, NM  87545
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