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Disease
study's focus on habitat
Chicago Tribune
- 8/4
When
Dr. John Snow removed the pump handle from a town well in London
in 1848, he wanted to prove two things: Water from the contaminated
well was spreading cholera, and forcing people to drink clean
water would stop the deadly epidemic.
He
was right on both counts.
Today
medical scientists stumped by more modern epidemics--including
asthma, autism, retardation, attention deficit hyperactivity disorder,
diabetes, childhood cancer, depression and schizophrenia--are
turning again to Snow's tactics.
Researchers
are planning what could become the largest, most intense and costliest
study ever undertaken to find out if many, and possibly most,
diseases are linked to environmental exposures that occur as early
as conception and continue during fetal development and early
childhood.
They
are launching a massive search of children's neighborhoods for
what might be causing the alarming increases in these health problems.
Expected
to get under way in 2005 or 2006, the study will cost an estimated
$3 billion, the approximate price tag of the Human Genome Project,
the ambitious effort to decipher all human genes.
Drawing
on the latest advances in genetic science, researchers will attempt
to draw connections among infants' genes, environmental exposures
and subsequent diseases. The goal is to develop ways to better
prevent and treat the ailments.
"A
big study like this provides an opportunity to study all of the
determinants of these kinds of problems, from the lead paint in
your house to the water quality to the social structure of your
family, your neighborhood, your diet, poverty, all of those things
that contribute to health in the population," said Gwen Collman,
scientific program director of the National Institute of Environmental
Health Sciences.
"If
you conduct a well-designed longitudinal study, you can weigh
all of those factors and look at the complex interactions between
them," she said.
Called
the National Children's Study, the research will involve 100,000
children and their families as well as the resources of NIEHS,
the National Institute of Child Health and Human Development,
the Environmental Protection Agency and the Centers for Disease
Control and Prevention.
The
study will include women before they conceive in order to study
environmental conditions that may have an impact on conception.
Environmental influences will be monitored throughout pregnancy
and during the first 21 years of each child's life.
"We
now have probes that will help us characterize the genetic factors
of disease, and we can measure environmental exposures and body
concentrations of a broad range of chemicals," said Dr. Donald
Mattison of the National Institute of Child Health and Human Development.
"We're
getting better at characterizing stress, and we're getting a better
understanding of what the impact of a family structure is on growth
and development," he said. "We now have some beginning
understanding of the way that these exposures might be linked
to health outcomes later in life."
How
genes and the environment can combine to cause a common disease
was recently reported by University of Wisconsin scientists. They
found that people who inherit two copies of the short version
of a gene that regulates serotonin, an important neurotransmitter
involved in mood control, are 2 1/2 times more likely to become
depressed under typical life stresses than people who inherit
the long version.
Fragility
of fetal development
Scientists
know that fetal development is a time of extreme vulnerability
to outside influences. A single cell multiplies into a baby with
100 billion cells in nine months as genes issue trillions of instructions
in response to chemical messages cells send and receive.
When
wrong messages are sent, it can have disastrous effects on the
forming nervous system and body, such as when excessive alcohol
consumption by pregnant women results in fetal alcohol syndrome.
"There
is growing evidence suggesting that adult diseases or the risk
factors for adult diseases are influenced substantially by fetal
well-being," Mattison said.
Infancy
is another critical period, especially for the rapidly developing
brain, which can be stunted by even modest amounts of lead poisoning,
a continuing threat to 1 million American children.
Even
childhood infections can set the stage for adult diseases. Eighty-five
percent of peptic ulcers in adults, for instance, are caused by
a childhood infection with H. pylori bacteria, which may smolder
for decades as a symptomless infection of the stomach lining.
Now
scientists will study other childhood infections to see if they
are linked to adult heart disease, cancer and diabetes.
They
also will look for the ways in which genetic susceptibilities
and environmental triggers interact to result in disease. Obesity
and lack of exercise, for example, are major risk factors for
type 2 diabetes, which is reaching epidemic proportions in children.
Yet it is clear that there is a strong genetic susceptibility
for the disease, since only 15 to 30 percent of obese people become
diabetic.
The
University of Chicago's Graeme Bell is searching for the genes
that predispose people to diabetes, hoping the information could
help develop strategies to prevent the disease in those at risk.
"We
will be able to tell one individual with certain genetic risk
factors for diabetes that he should avoid a high-fat diet and
another, who has a different genetic risk, that he should exercise
a little more," Bell said.
Even
normal genes can cause problems when they are exposed to bad environments.
Radiation and some toxic chemicals can damage genes to cause cancer,
for example.
Scientists
have discovered about 200 of these kinds of genes, called environmentally
responsive genes, which increase the risk of such chronic conditions
as cancer, heart disease, diabetes and asthma.
Exposure
to chemicals
Among
the other factors the researchers will consider is the effect
of chemicals in the environment, such as whether herbicides may
be implicated in Parkinson's and Alzheimer's diseases.
"Children
have greater exposure, pound for pound, than adults to environmental
toxins because of their metabolism, their hand-to-mouth behavior
and the fact that they often play close to the ground," said
Philip Lee, consulting professor in the Program in Human Biology
at Stanford University.
Since
the 1950s the number of chemicals people may come in contact with
has increased dramatically. The EPA estimates that 10,000 to 15,000
chemicals are in general use for making various products or as
part of manufacturing processes. So far 1,500 have been withdrawn
from use because of potential harmful effects.
The
latest CDC study on human exposure to environmental chemicals
found that a random sample of Americans had traces of 116 chemicals
in their urine. The EPA reports that 8 percent of women of childbearing
age have levels of mercury in their blood that could stunt a fetus'
brain development.
There
is no question that chemistry has improved life, but the downside
to the chemical revolution is that the majority of chemicals have
not been adequately tested for toxic effects, said Dr. Philip
Landrigan, head of community and preventive medicine at the Mt.
Sinai School of Medicine in New York.
"One
of the things that people like me worry about is the notion that
kids are being exposed today to toxic chemicals whose effects
we haven't yet been smart enough to recognize," he said.
"And we always wonder if there are various nasty surprises
lurking out there because we've really been careless about testing
these chemicals."
In
a study reported in May in the journal Environmental Health Perspectives,
Landrigan and his colleagues estimated that just four diseases
linked to environmental exposures--lead poisoning, asthma, childhood
cancer and learning disabilities--cost Americans $54.9 billion
annually.
The
costs include direct medical care and lost income from death or
such disabilities as the lowered IQ potential caused by lead toxicity
to the central nervous system.
Lead
poisoning accounts for $43 billion of the annual loss because
the link between environmental exposure to the heavy metal and
brain damage is clear, Landrigan said. Environmental causes of
the other diseases are based on preliminary findings, but for
asthma there is already a strong link with outdoor and indoor
air pollution, he said.
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