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Where 'can' and 'should' face off

Disease screening can flag genetic rarities such as Tay-Sachs, and is urged in high-risk groups. Does broader testing make sense?

January 16, 2006|Kate Shatzkin | Baltimore Sun

The cherry-red spots on the baby boy's retina told a tale of genetic catastrophe: Conner Hopf, 11 months old, almost surely will not live to see his fifth birthday.

Before he dies, he's likely to go blind, lose much of his hearing and become unable to move. He has a rare degenerative disease known as Tay-Sachs, which once principally struck children of Eastern or Central European Jewish heritage.

A 30-year-old nationwide screening program for prospective parents has been so effective that the number of Tay-Sachs babies born to parents who identify themselves as Jewish has fallen by 90%. But that still leaves about 20 children diagnosed with Tay-Sachs in the U.S. each year.

At least two-thirds do not fall into Jewish or other ethnic groups with a high risk for the disease.

The current face of Tay-Sachs, one of the first genetic diseases to meet criteria for a public prevention program, shows the possibilities and the limits of carrier and prenatal testing for genetic disease.

Even as screening for many inherited maladies becomes available, scientists, physicians and patients must wrestle with how much they want to know -- and at what cost.

For example, the American College of Obstetricians and Gynecologists recommends making information about carrier screening for cystic fibrosis available to all couples who seek prenatal care.

The recommendation is universal, even though members of some ethnic groups, such as Asian and African Americans, have relatively little risk of producing a child with the disease.

But the organization's recommendation for Tay-Sachs screening extends only to people in a high-risk ethnic group or with a family history of the disease.

Scientists debate whether to make screening more widely available when the overall risk of giving birth to a Tay-Sachs child in the general population is so low.

"I think we're coming to that time that there has to be a very serious discussion about this," said Dr. Susan J. Gross, co-director of the Division of Reproductive Genetics at Montefiore Medical Center and an associate professor at the Albert Einstein College of Medicine in New York.

"Here's a disorder with a very effective screening test. It's very cheap, and you do it once in your lifetime.... Some people may feel that allowing a certain number of Tay-Sachs disease cases every year is acceptable. I can't say that."

The American College of Medical Genetics in Bethesda, Md., is reexamining its standards on carrier screening for diseases based on ethnicity, said executive director Michael S. Watson.

"The way we developed cystic fibrosis screening is as a pan-ethnic panel," he said. "That's certainly the direction in which we're trying to think about all areas of screening."

But Dr. Michael Kaback, who pioneered the mass screening of Jews for Tay-Sachs, said more widespread testing was not a practical way to prevent the few cases that remain.

"It is not medical practice in America today to offer every screening test to every couple for every disease," said Kaback, now a professor of pediatrics and reproductive medicine at the UC San Diego School of Medicine and director of California's Tay-Sachs prevention program. For couples outside the high-risk ethnic groups, he said, "it's a risk that's extremely low. If one were to take action on such low risks, one would never leave their house."

Tay-Sachs is caused by the absence of Hex A, a vital enzyme. Without it, fatty substances accumulate in the nerve cells of the brain, eventually destroying them. In its most common infantile form, the disease begins its damage in the womb.

For a child to have Tay-Sachs, both parents must carry the gene. Each of their children has a 1-in-4 chance of having the disease, and a 50% chance of carrying one copy of the gene but living a normal, healthy life.

Couples who know they carry the gene before they have children can decide whether to adopt, stay childless or have an embryo or fetus tested for the disease -- and possibly terminate the pregnancy.

Desiree Hopf had been adopted and didn't know much about her family history. Neither she nor her husband took a blood test to determine whether they carried the recessive gene. Nor were they aware that non-Jewish ethnic groups could also carry it.

Before they knew Conner was sick, the Hopfs bought a rambling playground set and laid rubber mulch below it. They expected their son to climb on it with his now 2 1/2 -year-old brother, Brenden -- who does not have Tay-Sachs -- for many years to come.

"They were going to grow up and play sports together," their mother said.

Though he is losing his eyesight, Conner still responds to family and friends with an enthusiastic smile. The Hopfs make the most of moments with him that other parents might take for granted.

They let Brenden sit and cry for short periods as he grew more independent, but someone holds Conner almost all day long.

But as much as they cherish their younger child, the Hopfs said that if they had known they were Tay-Sachs carriers, Conner would not have been born.

"I would never have chosen to bring a child into the world like this," Desiree Hopf said. "We're forced to sit here and watch him deteriorate."

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