SPATE OF DOWN CASES MYSTIFIES TEXANS

Because so many toddlers in the early childhood intervention program had Down syndrome - a chromosomal birth defect - their parents formed a support group.

But not until they drew a map to their first meeting did the eight families question whether their numbers were too high."We were all within 10 miles of one another," said Jill Buie, 29, a physical therapist whose family ranch straddles the Waxahachie city limits south of Dallas. "On the map, everyone lived just down the same road . . . Farm Road 664. . . . It was just really eerie."

A state health department investigation, prompted by a call from the parents, confirmed the observation, but officials say they are mystified what caused the high concentration.

Down syndrome, a birth defect that appears once in every 1,000 births, had occurred in Ellis County 2.3 times per 1,000 births - more than double the expected rate.

From 1992 through the end of 1994, at least 10 women in this rural area gave birth to Down Syndrome babies, according to the state health department's Texas Birth Defects Monitoring Division.

Eight of the births were clustered within a 13-month time period.

Three of the babies were born to mothers 34 or older, an age group at greater risk for Down syndrome. However, age was factored into the statistical ratio that has health investigators planning follow-up interviews.

Peter Langlois, senior epidemiologist with the Texas Birth Defects Monitoring Division, said his staff is investigating the cluster for risk factors such as lifestyle, medications, drinking water and factory emissions that could link the Down syndrome births.

He said parents expressed environmental concerns because the county is home to cement kilns that burn hazardous waste for fuel, an aluminum plant and a fiberglass factory, which is visible from the Buies' ranch.

"Can I tell you if there's any causal relationship? No, not at this stage," the epidemiologist said. "The vast majority of times," he said, investigations into clusters of Down syndrome births "don't turn up anything."

Eight of the youngsters are enrolled in "Step By Step," an early childhood intervention program offered at the state school in Mexia, Texas. They are the nucleus of the support group.