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Hi All,
A new twist on
genetic inheritance.
Bob.
Grandpa's Poisons May Affect You, Rat Tests Show
USA: June 3, 2005
WASHINGTON - Toxic chemicals that poisoned your grandparents, or even
great-grandparents, may also affect your health, US researchers suggested on
Thursday.
A study in rats shows the effects of certain toxic chemicals were passed on
for four generations of males.
The finding, published in the journal Science, suggests that toxins may
play a role in inherited diseases now blamed on genetic mutations.
"It's a new way to think about disease," said Michael Skinner, director of
the Center for Reproductive Biology at Washington State University in
Pullman.
"We believe this phenomenon will be widespread and be a major factor in
understanding how disease develops."
For their study, Skinner and colleagues injected pregnant rats with
vinclozolin, a fungicide commonly used in vineyards, and methoxychlor, a
pesticide that replaced DDT.
Both are endocrine disrupters -- synthetic chemicals that interfere with
the normal functioning of reproductive hormones, notably testosterone and
estrogen. Animal studies have shown they can affect fertility and the
development of genitals, for example.
Scientists knew that treating pregnant rats with high doses of vinclozolin
every day produces sterile male pups.
Skinner's team injected vinclozolin into pregnant rats during a specific
time during gestation when the developing embryos take on sexual
characteristics. "It is when either an ovary or testes develop," Skinner said in
a telephone interview.
The time was comparable to mid-gestation in humans.
Male rat pups born to these mothers had a 20 percent lower than normal
sperm count, their sperm were less motile, meaning they did not swim as well,
and they were less fertile.
There were similar results with methoxychlor.
When these male offspring were mated with females that had not been exposed
to the toxins, 90 percent of the new male offspring had similar problems. The
effect held for a fourth generation.
That has never been seen before, although radiation and cancer chemotherapy
are known to affect fertility and the children of people affected.
Radiation can also cause "germline" genetic mutations -- mutations in DNA
in egg and sperm cells that can be passed from one generation to the next. But
it happens only rarely.
"What we appear to have done is re-program that germline and that
re-programming is permanent," Skinner said.
These changes were not mutations, Skinner's team said. Instead, they were
changes in a process called methylation, in which chemical compounds attach to
and affect DNA.
The timing is important, too, Skinner said. When they injected the
chemicals into the rat mothers later in gestation, there were no changes in the
pups.
Now his team is studying the genes that are affected. Preliminary evidence
in the rats suggests that genes known to affect diseases such as breast and
prostate cancer may be affected by this process.
They also plan to see if other chemicals can have the same effects.
"It is important that we say these are preliminary studies," Skinner
stressed. The levels of chemicals the rats were exposed to were very high --
much higher than people normally ever encounter.
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