| Corn toxin examined in border birth
defects
Diet may have put Hispanics at risk
03/04/2001
By Laura Beil / The Dallas Morning News
AP file
photo
Judy
Guerrero's daughter Justine, shown at age 6 in McAllen in 1997,
was born with spina bifida. A '91 border birth defect outbreak
is unsolved.
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The nurses at Valley Regional Medical Center in Brownsville sensed
something more than a horrible coincidence. Two babies born the same day
in April 1991 had brains that were stunted or missing, a rare defect
that usually strikes only three or four births in 10,000.
Stunned, nurse Connie Riezenman called the Texas Department of
Health. Before state officials could respond hours later, doctors had
delivered a third, tragically malformed infant.
"I felt frantic," she said. "It was just too
scary." In the next six weeks, three more women gave birth to
misshapen newborns at her hospital.
State and national investigators would eventually find that
Brownsville had an astonishingly high rate of anencephaly, as the
condition is called. From 1989 through 1991, 32 women in this town of
130,000 carried anencephalic babies. Many of the children died within
hours, and all within days, of birth.
Then, in 1992, the anencephaly rate ebbed as unexpectedly as it had
risen.
Still searching for a cause, many experts keep circling back to one
of the few explanations for an epidemic that can come and go on its own:
a natural poison that crept in and out of the food supply. Disease
investigators have focused on a common toxin found in corn, a mainstay
of a traditional Mexican-American diet. If this toxin is indeed
responsible for the birth defects that stalked the Lower Rio Grande
Valley – and no one has yet concluded that it is – then Texas health
officials worry about other effects in Hispanics. In addition to birth
defects, the chemical may increase the risk for esophageal and liver
cancer.
The outbreak of 1991 remains unsolved. From the beginning, many
residents suspected the pesticides that armor nearby fields of cotton
and sorghum. Others blamed the chemicals that waft from industries along
the Rio Grande. Some parents of affected infants even shared a $17
million settlement from more than 80 maquiladoras – U.S.
factories hugging the Mexican side of the river – in 1995.
But now, state health officials wonder whether the culprit was not
man-made, but a natural fungus that can cling to corn. The fungus makes
a toxin, called fumonisin, unknown to science until 1988.
| Cameron
County birth defects: Possible pieces to the puzzle |
The
outbreak of neural tube birth defects struck Cameron County in
1990 and 1991. State health investigators are now examining
whether the outbreak might have been connected to fumonisin.
High levels of the toxin fumonisin can occur in corn crops grown
in hot and dry weather, followed by stretches of high humidity.
The toxin is a suspected contributor to neural tube birth
defects, and esophageal and liver cancer.
Mexican-American women along the border eat, on average, about
110 corn tortillas a month.
Liver cancer rates among Texas Hispanics are two to three times
that of other racial and ethnic groups.
Cameron County's rates of one type of neural tube defect,
anencephaly, rose from nine of every 10,000 births in 1988 to
almost 25 per 10,000 in 1991.
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Texas health officials learned of it 1992. "We didn't even know how
to spell it," said Dr. Kate Hendricks of the state's
infectious-disease division. Since then, Dr. Hendricks and her
colleagues have found themselves becoming armchair authorities on corn
mold.
Given fumonisin's potential to cause disease, a United Nations
committee will soon release its first report recommending a daily limit
on human exposure to the toxin. Last summer, the U.S. Food and Drug
Administration announced possible guidelines for the maximum amount of
fumonisin in corn intended for human food. The agency recommends no more
than 4 parts per million for masa and similar corn products.
But the FDA number, state officials argued in a three-page response,
may be too high for those who depend on corn for their daily bread.
"There is clear evidence," state officials warned, "that
fumonisins are carcinogenic in some animal species and sufficient
evidence indicating that these compounds may be able to affect the
neural development of the fetus."
They urged that any decision on fumonisin levels "take into
consideration the consumption patterns of the Texas Hispanic
population," concerns that FDA officials say they are heeding.
Tracking the poison
Fumonisin (pronounced few-MAHN-i-sin) is spit out by the mold Fusarium
as part of its chemical defense system. For decades, farmers and
ranchers have known that animals can fall seriously ill if they eat corn
that has been coated with Fusarium, even if the kernels later
seem clean. People in parts of the world with high Fusarium growth,
most notably the Transkei region of South Africa, have high rates of
esophageal cancer.
But it wasn't until 1988, when South African scientists first
described fumonisin, that anyone knew exactly why the mold was
dangerous.
One of the more peculiar traits of fumonisin is its ability to cause
vastly different diseases in different animal species. Pigs that eat
fumonisin-contaminated corn can develop pulmonary edema, a condition in
which their lungs fill with fluid. The most sensitive animals appear to
be horses, which get a crippling brain disease called
leukoencephalomalacia.
In humans, hints of the esophageal and liver cancer risks come from
studies in rats, and from parts of the world – such as the Transkei
and certain areas of China – with frequent fumonisin contamination of
corn. Health officials note that these regions also have high rates of
the same birth defects that appeared in the Rio Grande Valley. But this
kind of research doesn't address the possibility of a coincidence.
Possible fetal effects
Anencephaly, which befell Brownsville's babies, is one of a
cluster of abnormalities called neural tube defects. The most common is
spina bifida. The defects occur soon after conception, at a time when a
woman wouldn't even know she is pregnant. They happen when the cells of
the embryo that will create the central nervous system don't wrap around
themselves and form a tube during development. Sufficient levels of
folic acid, a B vitamin, will protect against neural tube defects.
In 1997, researcher Victoria Stevens of Emory University in Atlanta
offered a possible connection between fumonisin and folic acid. In
test-tube experiments, she found that fumonisin interfered with a cell's
ability to absorb the vitamin. If this is true in the womb, then
fumonisin might starve a developing embryo of its protection.
"There's a biologically plausible mechanism," Dr. Stevens
said. She is quick to add, however, that this is only a theory, and hers
only one study. Without a lot more research, no one can say whether what
happens in a laboratory is actually what causes neural tube defects
during pregnancy.
While lacking proof that ties fumonisin to the tragedy along the
border, Texas health officials are nonetheless impressed by the
circumstantial evidence. For one thing, if pollutants caused the birth
defects, why, then, did the outbreak subside? Surveys found that even
after folic acid awareness campaigns, childbearing women of Brownsville
had not begun to dramatically supplement their diets with the nutrient.
"Whatever caused that [outbreak] ... didn't stay there
forever," Dr. Hendricks said. "Man-made chemicals would not
have disappeared."
Corn connections?
Fumonisin, however, is as unpredictable as the weather. Fusarium
mold grows on corn plants under stress from heat, insects or other
causes. In 1988, a blistering drought left corn farmers with one of
their worst harvests in years. Crop reports show that by August and
September, about half the country's cornfields were listed as
"poor" or "very poor." Conditions improved in 1989,
with more than half the late-summer crops described as good or better.
Still, no one can say whether corn plants themselves from the late
1980s were contaminated. Agriculture officials do know that in late
1989, corn-fed horses across the nation began dying from
leukoencephalomalacia, or ELEM. "We began to get daily phone calls
from state labs, veterinary hospitals with what they regarded as ELEM
cases," said Frank Ross, head of toxicology for the National
Veterinary Services Laboratory in Ames, Iowa. "We would typically
hear of a few of these a year." The outbreaks lasted through the
winter of 1990.
Recognizing the fingerprints of fumonisin, Dr. Ross' laboratory found
that toxin levels in corn-based horse feed at the time typically
exceeded 10 parts per million. Some reached the surprising level of 126.
Also in 1989, an unusual number of pigs began contracting pulmonary
edema. Iowa State University researchers found that fumonisin in corn
needed to rise above 50 parts per million to give pigs the deadly lung
disease.
At the same time livestock were falling ill from fumonisin, neural
tube defect rates around Brownsville were creeping upward, mostly driven
by rises in anencephaly. But no one would notice this trend until the
three births at Valley Regional summoned state and federal disease
investigators in 1991.
Then, in 1992, the state chemist called Texas health officials. Did
they know that a state screening program for animal feed was finding
fumonisin levels approaching 70 parts per million? Operators transferred
the call to Dr. Hendricks. "Fumonisin?" she asked, puzzled.
She and her colleagues began scouring for information.
"What we read made us very concerned," Dr. Hendricks said,
their thoughts lingering on the border outbreak. If fumonisin had
infiltrated the corn supply, they reasoned, the most serious effects
would show up in the biggest corn eaters. Canadians, who eat only about
17 grams of corn a day on average, probably wouldn't need to worry. But
Mexican-American women along the border eat more than five times that
amount per day in tortillas alone.
By this time, the border outbreak had quieted. Plus, no one could
test corn eaten in 1989 and 1990, about the time women affected by the
outbreak would have become pregnant.
Tortilla tests
A continent away, though, researchers in South Africa had already
screened corn from the U.S. food supply. By coincidence, they were
studying fumonisin levels in five countries. They bought corn in various
incarnations – including tortillas – in 1990 and 1991. The
researchers found fumonisin in one-third of the U.S. tortillas they
tested. The concentrations were less than 1 part per million;
nonetheless, the fumonisin content of most of the U.S. corn products
dwarfed amounts in the products from other countries. The South African
samples generally had the second-highest levels.
The findings, scientists wrote in 1991 in the Journal of
Agricultural and Food Chemistry, "clearly indicate for the
first time that consumers of corn-based commercially available
foodstuffs in the United States and South Africa are exposed to elevated
levels of the fumonisins."
The numbers might be even higher were it not for the slow journey
from corn to masa to tortilla. Ancient methods of steeping,
washing and grinding transform corn and water into an enchilada wrapper
or crispy chip. During the half-dozen or so stages, the kernels take a
long, hot bath in lime and shed their hulls. These steps drastically
reduce fumonisin levels.
Studies led by USDA scientist Mary Ann Dombrink-Kurtzman in Peoria,
Ill., have found that tortilla making can slash the level of fumonisin
in raw corn by as much as 80 percent. To come up with that number, she
and Texas A&M University researcher Lloyd Rooney took samples from
laboratory-made tortillas at every point from corn through oven.
However, she notes, "this doesn't answer what people in their
homes may be doing during their processing."
Over the last three years, Dr. Dombrink-Kurtzman has examined nearly
2,000 cornmeal samples from the U.S. milling industry, gathered amid
routine, voluntary screening for fumonisin that started in 1998. Given
the levels she has found, along with the reductions through cooking, she
has calculated that U.S. corn tortillas these days would contain between
0.02 and 0.2 parts per million.
"I still eat a lot of tortillas," Dr. Dombrink-Kurtzman
said. "I think the corn is safe." However, her studies of
Mexican masa and tortillas have found much greater
concentrations. Some of those samples approached 2 parts per million.
These higher figures, she said, might be expected from regions where
drought often strains corn crops.
Hispanic health
These and other recent analyses suggest that current fumonisin
concentrations in tortillas are low. But Texas health officials also
think about their research showing that Hispanic women along the border
eat, on average, about 110 corn tortillas a month.
Still, if corn is a staple among Mexican-Americans across the state,
why would fumonisin's damage show up only in Cameron County? No one can
say with certainty that Brownsville was unusual, Dr. Hendricks replies.
Before 1993, birth defects were not carefully monitored in Texas, or in
most places across the country, she said. "You can miss an increase
rather easily."
"You have to think why we got called," she added. Had the
three terrible births at Valley Regional hospital not occurred, the
outbreak might have escaped notice.
There are some signals that more anencephalic births than usual were
occurring nationwide in 1991. The available data suggest that the
national rate was about 18 per 100,000 births that year. The number fell
to 13 in 1992, where it has more or less hovered, dropping as low as 10
in 1998.
Available records also suggest that across Texas in 1992, Hispanic
mothers continued to have anencephaly rates more than twice those of
non-Hispanic whites and three times those of black mothers.
Texas health officials acknowledge that none of this proves that
fumonisin caused the outbreak a decade ago. "It's a strong
hypothesis," Dr. Hendricks said.
Skeptical, but ...
Some of the country's top fumonisin experts remain intrigued, but
unconvinced.
"What do we know? We know there was a spike" in fumonisin
in 1989 corn, said Dr. David Miller of the Carleton University in
Canada. "We know the potential exists" for a connection to
neural tube defects, given the Emory experiments.
But he adds, "We have to be careful about associations."
The USDA's Ron Riley, who also studies fumonisin, is skeptical about
any link, largely because animals eating the toxin don't appear to get
birth defects. "We know that pigs eat a lot of [low-quality] corn
... but I've never seen a report of a neural tube defect."
Yet he believes the idea calls for further scientific investigation.
"I don't want there to be a connection," Dr. Riley said.
"There's a lot to lose if we start talking about corn being bad
food. ... My gut feeling is there's no connection, but I keep coming
back to the 'what if?' "
"What if?" also nags Texas health experts. No one doubts
that fumonisin causes disease in a variety of animals, Dr. Hendricks
said. It would be unlikely that people are somehow spared. Federal
officials, when setting the safety thresholds for fumonisin, should
think carefully about those who depend largely on corn, she and her
colleagues contend.
FDA officials say they are doing this.
"Yes, we are mindful of corn consumption by particular
population groups," said Mike Bolger, of the agency's Center for
Food Safety and Applied Nutrition. "We had that in mind when we
came up with this level." He said any tie to neural tube defects or
cancer is, for now, little more than a theory.
"We're not saying fumonisin is a non-problem," Dr. Bolger
said. "We're spending time, resources and energy to figure out
what's going on."
For 10 years, families along the border have also wanted to know
what's going on. "People think it was something in the water,
something in the air," nurse Riezenman said. But until anyone gives
them an answer, they will wonder whether an epidemic will suddenly
strike their babies again.
"Like any community that's experienced something dreadful,"
she said, "it's always in the back of your mind."
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