BROWNSVILLE, TEXAS — BROWNSVILLE, Texas -- In less than 36 hours last spring, three children were born without brains at Valley Regional Medical Center here.
Two of the babies were stillborn. The third hung on for three days, doomed by a gruesome, fatal defect that leaves infants with an open skull and only the rudiments of a brain.
The deaths from the rare defect, known as anencephaly, puzzled Margaret Diaz, an occupational health specialist. She thought the three cases could have been a statistical fluke. Then, she had a chance conversation with a radiologist.
He had recently performed ultrasound examinations on seven pregnant women. Each, he said, was carrying a child without a brain.
Doctors soon learned of at least 10 more cases, most of them clustered in this city of 98,000 along the Rio Grande. The outbreak here and in surrounding Cameron County may be the " largest ever in the United States.
Across the river in Matamoros, Mexican health officials are worried, too.
Two anencephalic children were delivered at the general hospital in 1990, but 10 were born last year.
Dr. Diaz's alarm has prompted full-blown investigations by the U.S. Centers for Disease Control, three Texas agencies and a local group of lawyers, doctors and chemists. So far, they have few answers.
"We think something terrible happened to cause this, but we don't know what it is," said William Lipps, a Brownsville chemist assisting the CDC.
But some here have their suspicions. Long uneasy about the heavy pollution in their sister city of Matamoros, Brownsville residents now fear that an environmental time bomb has gone off.
Like other Mexican border towns, Matamoros is struggling under the residue left by years of unchecked industrial growth.
It is dominated by U.S.-owned companies that came south over the last three decades for cheaper labor, favorable trade rules and lax enforcement of environmental laws. Today, Matamoros is an ugly sprawl of industrial plants and shacks housing Mexican workers. Its open sewers contain toxic wastes and human refuse. Its factories spew fumes and leak chemicals.
While CDC experts are considering environmental factors in their investigation of the outbreak, they say that the inquiry is in its early stages and that they have no evidence linking the deaths to the chemical stew in Matamoros.
"It would be a tremendous medical breakthrough if we could find what caused just half of those Texas cases," said Dr. Gregg Sylvester, a Johns Hopkins-trained epidemiologist who is leading the investigation. "I suspect that the causes of anencephaly may involve a multitude of factors and that we won't find a single cause."
Even as the medical detectives search for answers, the tragedy is unfolding. Another anencephalic baby was born at Valley Regional on Christmas Day.
To the parents of the children, the horrible nature of the defects is devastating. "Many of the patients were poor Mexican-American women who had no idea what to expect," said Vikki Barton, the head nurse in the hospital's nursery.
"It is very shocking when you're expecting a normal baby."
Doctors know that anencephaly occurs in the early days of pregnancy as the brain and spine are formed. But they don't know what triggers the defect.
A British study last year established that folic acid -- a vitamin found in green leafy vegetables, bread, rice, citrus fruit and nuts -- is critical in the first weeks of pregnancy. The study showed that adding folic acid to the diets of high-risk mothers sharply reduced their chances of producing anencephalic babies.
Researchers have also shown that exposure to solvents -- chemicals used to clean or mix in paint, plastics and electronics factories -- has been linked to central nervous system defects. A 1979 Finnish study tied such defects to a mother's exposure to solvents.
More recently, epidemiologists at the Texas Department of Health found in a 1990 study that men who used solvents faced higher risks of fathering anencephalic children.
If those men bore Spanish surnames, the risk was even higher, as much as four times greater than that of men not exposed to solvents.
The findings about solvents raise suspicions because preliminary test results show residues of heavy concentrations of organic solvents in the soil around Matamoros and in the Rio Grande.
Investigators in the Texas outbreak are theorizing that exposure to some chemical or other environmental or genetic factor prevented the Brownsville mothers from having sufficient folic acid in the crucial first weeks of pregnancy, said Dr. James E. Cheek, a CDC epidemiologist.
The scientists are also trying to discover if there is a predisposition to anencephaly among Mexican-Americans, since the defect occurs in Mexico at nearly six times the U.S. rate. Even so, other factors may be involved because no anencephalic outbreaks have occurred in similar Mexican-American border populations in California, New Mexico or Arizona.
Dr. Carmen Rocco, a Brownsville pediatrician assisting the CDC, has marked a map of the city of Brownsville with 15 dots, each representing a woman who conceived an anencephalic child between July 1990 and January 1991. All lived within a mile of Matamoros.
"I am convinced some event or events occurred during that time, something in the environment that cannot be explained," she said.
Between 1986 and 1988, Cameron County averaged an estimated five anencephalic cases per 10,000 live births, slightly higher than the U.S. average of 3.4.
But beginning in 1989, the numbers apparently grew nearly threefold, to as many as 15 a year, the preliminary data showed. Dr. Rocco estimates that the rate for Brownsville alone may be 10 times the U.S. average, or about 30 per 10,000 births.
Dr. Diaz, the occupational health expert, agrees that more babies may be affected than figures show. She estimated that as many as 40 percent of Cameron County women deliver their babies through midwives, many of whom are unregistered with the local health department.
Risking exposure, they would be reluctant to report any births. And a mother is unlikely to report an abnormal birth to authorities because Mexican culture stigmatizes women who produce deformed children.
Like Dr. Rocco, Dr. Diaz believes that the uncontrolled pollution in Matamoros -- with its scores of chemical plants and electronic assembly factories, many of which use solvents -- is to blame for the outbreak.
"These were atrocities committed by two uncaring governments," said Dr. Diaz of the anencephaly cases. "They are the product of years of neglect."
Indeed, environmental safeguards have remained primitive as Matamoros swelled over three decades from a town of 80,000 known for its cotton and brothels to an industrial city of 303,000 filled with companies like Zenith, General Motors and AT&T.;
The city's major thoroughfares, for example, are bordered by open sewers. They empty into a huge sludge pond -- there is no treatment plant. Chemical factories frequently dump toxic wastes or release poisonous clouds. Almost daily, air quality officials say, residents report odd odors.
Authorities say that hazardous materials, such as plastics, are secretly burned at night, and the city's huge landfill often catches fire. Additionally, there is frequent aerial spraying of insecticides, herbicides and defoliants on both sides of the border.
"If there were an environmental event or spike in the Matamoros area, would anyone know about it?" asked Mr. Lipps, the chemist and member of the investigation team. "We have only the most rudimentary air testing."
To Casimiro Vasquez, a Brownsville resident who lives just a half-mile from Matamoros, the questions raised by the medical mystery are particularly haunting.
He is the father of 9-month-old Bianca, who suffers from spina bifida, a nervous system defect closely related to anencephaly. She may never walk or control her bladder or bowels, doctors say.
"When she was born with this sack of nerves hanging off her back, we were scared that something evil had befallen us," Mr. Vasquez said.
"Then we heard from the doctors about these other cases -- these babies without brains -- and we thought: We are living through a truly great tragedy."
Anencephaly is among several birth defects of the neural tube, a narrow sheath that encloses the spinal cord and brain of an embryo between the third and fourth weeks of pregnancy.
Just before the neural tube is formed, the cells that will form the brain and spinal cord lie in a microscopic furrow of flesh, much like a delicate sleeping bag ready to be zipped.
As the week-long process begins, a two-way zipper encloses the sides of the sleeping bag, starting in the middle and working toward both ends. The head of the bag will become the brain; the foot will be the tip of the spinal cord.
If the zipper does not properly close over the brain, anencephaly results. Most children with the defect are stillborn. While an infant may live for a few days, the baby invariably dies because the thinking and coordinating hemispheres of the brain are poorly developed or nonexistent. A large portion of skull and scalp usually are missing and tissue is exposed.
If the zipper does not close at the foot, or spinal cord end, of the sleeping bag, it will produce the other major neural tube defect, spina bifida.
The effects of spina bifida can range from practically none to mental retardation, severe paralysis and sometimes death. It is the leading crippling birth defect in the United States.
The incidence of babies born with anencephaly has decreased dramatically in the last two decades due to prenatal testing. Most mothers elect to have abortions after discovering the defect through ultrasound tests or amniocentesis.
Just what causes neural tube defects has puzzled scientists for centuries. While the mother's diet and vitamin intake may play a role, researchers believe a number of factors are likely involved.
For example, anencephaly has tended to occur more commonly in certain areas. Rates in the United States are highest in the northeast and north central regions. High rates of anencephaly have occurred in England and Northern Ireland, as well as in third world countries including Mexico.
The U.S. Centers for Disease Control is conducting a five-year study of anencephaly in northern China, where the rates are 10 times higher than in the United States.