Environmental Toxin Causes Heritable Adult-Onset Diseases

[Guest guest]

Environmental Toxin Causes Heritable Adult-Onset Diseases

http://www.medicalnewstoday.com/medicalnews.php?newsid=52628

A disease you are suffering today could be a result of your great-

grandmother being exposed to an environmental toxin during pregnancy -

and you may already have passed it along to your children.

That's the conclusion reached by researchers at Washington State

University, who have found that exposure to an environmental toxin

during embryonic development can cause an animal, and almost all of

its descendents, to develop adult-onset illnesses such as cancer and

kidney disease. Their discovery suggests that toxins may have played

a role in the rapid increase in localized geographic areas of

diseases that were previously thought to be caused primarily by

genetic mutations.

" It's a new way to think about disease, " said K. Skinner,

director of the Center for Reproductive Biology. " If this pans out,

it gives us a host of new diagnostic and therapeutic tools. " He said

it also underscores the potential long-term hazards of environmental

contaminants.

The work is reported in two papers in the September 14 issue of the

journal Endocrinology. It builds on the group's 2005 finding that

exposure to a toxin during embryonic development can cause fertility

problems in male rats that are passed to later generations.

In the current study, Skinner and a team of WSU researchers exposed

pregnant rats to an environmental toxin during the period that the

sex of their offspring was being determined. At that stage of

development, the genes of the male embryo's sex cells (future sperm)

are uniquely vulnerable to reprogramming.

The researchers used vinclozolin, a fungicide commonly used in

vineyards. Vinclozolin belongs to the class of compounds called

endocrine disruptors, synthetic chemicals that interfere with the

normal functioning of reproductive hormones. Skinner's group used

higher levels of the toxin than are normally present in the

environment, but their study raises concerns about the long-term

impacts of such toxins on human and animal health, particularly in

exposures during early- to mid-pregnancy (6 weeks to 5 months in

humans). Further work will be needed to determine whether lower

levels have similar effects.

Pregnant rats that were exposed to vinclozolin produced male

offspring with low sperm counts and a high incidence of adult-onset

diseases. Despite their low fertility, those males were still able to

produce offspring. When they were mated with females that had not

been exposed to the toxins, their offspring had the same problems.

The effect persisted through four generations, with about 85 percent

of the offspring in each generation developing conditions such as

breast tumors, prostate disease, kidney disease, immune system

abnormalities, and premature aging. Some mice came down with just one

disease, but the majority suffered multiple ailments.

" Only the original generation mother was exposed to the environmental

toxicant, " said Skinner. " A human analogy would be if your

grandmother was exposed to an environmental toxicant during mid-

gestation, you may develop a disease state even though you never had

direct exposure, and you may pass it on to your great-grandchildren. "

The study shows the potential impact of so-called epigenetic

inheritance, which refers to the transmission from parent to

offspring of biological information that is not encoded in the DNA

sequence. Instead, the information stems from small chemicals, such

as methyl groups, that become attached to the DNA. In epigenetic

transmission, the DNA sequences - the genes - remain the same, but

the chemical modifications change the way the genes work and when

they " turn on " and " turn off. "

The team identified 25 segments of DNA in the affected rats that had

altered patterns of methyl groups compared to control rats. Their

results suggest the genes controlling susceptibility to the observed

diseases lie somewhere within those 25 segments. Skinner said the

broad-spectrum effect of the changes, causing diseases in many organ

systems, was a notable result that could provide valuable clues about

how diseases develop.

According to Skinner, such changes might play a role in human

diseases such as breast cancer and prostate disease, whose frequency

is increasing faster than would be expected if they were the result

of genetic mutations alone. Scientists have long known about

epigenetic changes, but their high rate of heritability and their

importance in the control of gene activity were not appreciated until

recently.

Skinner said the finding that an environmental toxin can permanently

reprogram a heritable trait also may alter our concept of

evolutionary biology. Traditional evolutionary theory maintains that

the environment is primarily a backdrop on which selection takes

place, and that differences between individuals arise from random

mutations in the DNA. The work by Skinner and his group raises the

possibility that environmental factors may play a much larger role in

evolution than has been realized before.

This research was supported by a grant to Skinner from the National

Institutes of Health.

[Guest guest]

Hello Gretchen,

This is scarier than the prospect of the Yellowstone volcano blowing

up.

EdM from NH

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