RE: Down Syndrome and Radiation Exposure

["Carlisle, Sara" <carlisles@aecl.ca>]

Steve:

Teratogenic effects are non-genetic effects induced by some factor, such as
the abnormal limb development induced by thalidomide without altering the
DNA.  Down Syndrome, on the other hand, is the result of genetic abnormality
- in particular, having three copies of a region of chromosome 21, so is not
a teratogenic effect but a genetic effect.

Although it has sometimes been suggested that Down Syndrome may increase due
to radiation, evidence does not seem to support this.  See, for example,
Johnson, K.C., and Rouleau, J. (1991) Tritium releases from the Pickering
nuclear generating station and birth defects and infant mortality in nearby
communities 1971-1988, AECB report INFO-0401. In this study of the
population of Pickering, Ontario, Canada (1971-1988), no evidence of
increased incidence for 21of 22 birth defects was found, and while a
"cluster" of Down's syndrome cases near Pickering were observed, the
affected births were usually followed in time by tritium releases, ruling
out causation.  Similarly, I don't believe the Atomic Bomb Survivor
follow-up has found an association between Down Syndrome and radiation
exposure.

Mental retardation and small head size, however, is associated with in utero
exposures between 8 and 15 weeks after fertilization, and to a lesser extent
from 16 to 25 weeks.  Such effects are associated with doses greater than
about 10 cGy (see Yamazaki and Schull, 1990, JAMA 264: 605-609 - I'm sure
there are more recent references, but this was the only one I could dig out
on short notice).  These effects are teratogenic rather than mutagenic, and
appear to be associated with disruption of neuronal migration during
development.

Hope this is helpful


Sara M. Carlisle
Radiation Biology and Health Physics Branch
AECL, Chalk River Laboratories
Chalk River, ON K0J 1J0
Canada

phone (613) 584-8811 extn 3667
fax        (613) 584-1713
email   carlisles@aecl.ca


> ----------
> From: 	steve hand[SMTP:hand@wam.umd.edu]
> Reply To: 	radsafe@romulus.ehs.uiuc.edu
> Sent: 	Thursday, June 10, 1999 11:21 AM
> To: 	Multiple recipients of list
> Subject: 	Down Syndrome and Radiation Exposure
> 
> 
> Anyone have information on whether Down Syndrome can be considered a
> teratogenetic effect ?  I have looked in NCRP 115, BEIR V and a few
> ICRPs dealing with diagnostic and therapeutic radiation harm to the
> reproductive organs and cells as well as the fetus.
> Should this be termed mental retardation instead of Down Syndrome, given
> the statement that no genetic effects have been found in human
> populations studied as a result of radiation exposure?
> 
> Thank you for the help - this is in response to a question from someone
> in one of our training classes requesting additional information.
> 
> 
> Steve Hand
> Radiation Safety
> University of Maryland
> 
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