Huh, this one popped up in my in-box after being
routed through some sort of time-vortex, apparently...
--- Dan Minette <[EMAIL PROTECTED]> wrote:
> Going back through the messages.
>
> From: "Deborah Harrell" <[EMAIL PROTECTED]>
>
> > But evidence that high levels of radiation cause
> > cancer and genetic damage is strong -
>
> IIRC, there is no indication after 50+ years of
> study that the children of
> men and women exposed to high levels of radiation
> from the two atomic
> bombings in Japan have a higher rate of illness or
> any other indication of
> genetic damage than a control group (as long as the
> child was conceived
> after the bombings). If that is what you meant by
> genetic damage, I will
> have to disagree. If you meant harm to the person
> exposed, I have no problem.
"Genetic damage" means permanent damage to any genes;
this is how most if not all cancers begin: with
alteration of one or more genes regulating cell
growth, cell response to regulatory chemicals, or cell
death. As you imply, radiation exposure in utero can
result in genetic damage/cancer; also mental
retardation and certain physical defects have been
found in Japanese who were exposed in utero.
Study of the adult children of Japanese survivors of
A-bomb exposure ("F1 population") is still ongoing;
this is a 1990 abstract:
http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=PubMed&list_uids=2366299&dopt=Abstract
"...For those members of the F1 population who were
less than 20 years old between 1946 and 1982, cancer
risk did not appear to increase significantly as
parental gonadal dose increased. Follow-up of this
population will continue to determine if the patterns
of adult-onset cancer are altered."
A 1996 update reports: "to date no evidence exists of
genetic effects in the children of A-bomb survivors."
http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=PubMed&list_uids=8800280&dopt=Abstract
Research is ongoing WRT heritable radiation-induced
genetic damage, in this case cancer surviviors who
were treated with radiation. Current knowledge is
based on less than 5000 such patients. Not mentioned
in this "the glass is half-empty" study is the likely
difficulty in separating germ-cell (ie. heritable)
damage that is caused by radiation vs. that caused by
certain chemotherapy agents (some of which do cause
cancer by altering cellular DNA).
http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=PubMed&list_uids=10331521&dopt=Abstract
"...Compared with exposures experienced by atomic bomb
survivors, cancer survivors have been exposed to
higher doses of partial body irradiation and
combination chemotherapy over longer periods. Thus,
cancer survivors provide a model system with which to
evaluate the long-term effects on the human organism
of high doses of agents known to damage DNA...However,
the late complications of cancer in long-term
survivors has been poorly evaluated, especially in
adults, and little is known of the most troubling
possibility, that is, that the effects of cancer
treatments could be passed on to the next generation.
What little we know comes from studies of at most
5,000 survivors of childhood cancer, treated decades
ago. So far, results are reassuring that with the
means now available, we cannot detect clinical
evidence of heritable damage. However, reproductive
effects, including infertility, are common
consequences of cancer therapy and may represent germ
cell damage. We are just in the infancy of studies of
germ cell mutagenesis in cancer survivors. The
relatively small numbers of survivors, and the few
types of exposures studied so far, provide only
limited grounds for reassurance..."
This is the study/compilation of the 4214 children
born to cancer survivors which found no evidence of
heritable disease (ie. "the glass is half-full" POV):
http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=PubMed&list_uids=12852473&dopt=Abstract
"...Coupled with prior studies, these preliminary
findings, if sustained by ongoing dose-response
analyses, provide reassurance that cancer treatments
including radiotherapy do not carry much if any risk
for inherited genetic disease in offspring conceived
after exposure."
Yet we know that low-dose radiation can cause
heritable damage in some human cell lines:
http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=PubMed&list_uids=12034319&dopt=Abstract
"...The studies indicate: (1) genetic instability
and/or heritable damage are induced in cells exposed
to radiation at a high frequency, and induction of
genetic instability is not limited to morphologically
transformed cells; (2) sensitivity to genetic
instability and heritable damage depend on cell type;
(3) checkpoint stringency and p53 status significantly
influence the frequency of radiation-induced genetic
instability and heritable damage; (4) in some cell
lines, damage induced by low doses of radiation (below
2 Gy) leads to heritable cytotoxic and genotoxic
effects in 100% of cells exposed. The data suggest
that mammalian cells misinterpret damage induced by
ionizing radiation as if it were a physiological cell
signal. This contrasts strongly with the response of
mammalian cells to damage induced by other types of
DNA-toxic agents where damage-specific repair
mechanisms are activated."
This study reports only 10% of exposed cells develop
'transmissible genetic instability:'
http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=PubMed&list_uids=10196663&dopt=Abstract
"Evidence is presented to support the hypothesis that
radiation may induce a heritable, genome-wide process
of instability that leads to an enhanced frequency of
genetic changes occurring among the progeny of the
original irradiated cell..."
So, a concern about the possible accumulation of DU in
various tissues (bone and kidney were among those
cited in the literature, IIRC) is that long-term
low-level radiation exposure of ovaries (or testicles,
but I think that because of the continual production
of sperm, this is less likely a concern) might well
cause non-lethal germ-cell DNA damage; if so, the
children conceived from those altered eggs *will* have
genetic damage in every cell of their bodies,
including their own eggs/sperm.
Interestingly, if the unaltered ("wild-type") p53 gene
is present in an irradiated cell, it may cease to
divide - i.e. the damage is contained and not passed
on. But if a mutant p53 gene is present, then the
cell continues to grow and divide, thus passing on the
defective/altered DNA. (This may explain at least in
part why we all aren't walking skin cancers, or
perhaps even why those exposed to external sources of
radiation have not developed identifiable heritable
DNA damage -- a single (or even multiple) exposure is
unlikely to damage the p53 gene of a particular cell.
An internal source, however, would have a much longer
time to alter the p53 gene, or others that might play
a similar protective role.)
http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=PubMed&list_uids=1323840&dopt=Abstract
"...A cause and effect relationship between expression
of wild-type p53 and the G1 arrest that occurs after
gamma irradiation was then established by
demonstrating (i) acquisition of the G1 arrest after
gamma irradiation following transfection of wild-type
p53 genes into cells lacking endogenous p53 genes and
(ii) loss of the G1 arrest after irradiation following
transfection of mutant p53 genes into cells with
wild-type endogenous p53 genes..."
It's possible that what "would be" heritable genetic
damage from radiation causes instead early embryonic
death...I know that miscarriages increased post A-bomb
and Chernobyl, but I wonder about workers exposed to
radiation...think that will have to be another time,
though!
Debbi
Almost Another L3 Maru ;)
__________________________________
Do you Yahoo!?
The New Yahoo! Shopping - with improved product search
http://shopping.yahoo.com
_______________________________________________
http://www.mccmedia.com/mailman/listinfo/brin-l
