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Geneticists are questioning the use of screening for certain hereditary diseases after new research showed that parents may be aborting healthy fetuses that test positive for a potentially serious but often treatable condition among Ashkenazi Jews.

The study, in this week's Journal of the American Medical Association, found that one-quarter of couples chose to terminate pregnancies after their fetus screened positive for Gaucher disease.

The enzyme deficiency syndrome can be debilitating in some cases, but is mild and treatable for most people. Doctors can't predict in utero which children will suffer and which will lead normal lives - they have to wait for symptoms to appear, such as bone pain, organ enlargement and anemia.

The study highlights a dilemma that families and doctors are increasingly facing as researchers uncover more and more genes for particular diseases.

Some gene discoveries are leap-frogging ahead of other important discoveries, such as treatments and accurate assessments of how likely it is that the gene will contribute to an illness.

For example, Huntington's disease - a neurological disorder - can be screened for but not cured. And in the case of Gaucher disease and other genetic syndromes, such as hereditary hemochromatosis, people may test positive but that doesn't necessarily mean they'll get the disease.

In those cases, say some experts, screening may do more harm than good.

"There are some people who are going to be aborted unnecessarily," said Ernest Beutler, who has treated Gaucher patients for 40 years and is considered a leading authority on the disease.

Children who are born may face stigma, unnecessary medical prodding or coddling by their parents, he added.

Screening for Gaucher disease is being offered in Canada, usually to those who have a family history of the disease or are of Eastern European Jewish descent.

Dr. Beutler, author of an editorial accompanying the JAMA study and chair of the department of molecular and experimental medicine at the Scripps Research Institute in California, is among those who say in the vast majority of cases, screening for Gaucher disease should be avoided.

They include Roderick McInnes, scientific director of the Institute of Genetics, part of the Canadian Institutes of Health Research.

"We can identify these carriers, but since most of them don't get the disease, the decision of most geneticists around the world is we shouldn't be testing for them," Dr. McInnes said. "There are economic costs, and costs to the family."

But others say abandoning the testing would unfairly deny couples genetic information about their offspring. "I think it's good to know," said Kathy Siminovitch, director of genomic medicine at Toronto's Mount Sinai Hospital. "Even if you don't treat the child, the doctor is aware of it, the doctor will watch for symptoms."

Of the thousands of patients referred to her clinic annually, she says, most choose to be screened for a variety of genetic diseases, including Gaucher disease, because they'd rather be prepared - even if there's a small chance of becoming ill.

Greg Macres and his wife, Deborah, were among the unlucky ones. By the age of 1, their second child, Gregory, was vomiting frequently and developing more slowly than they had observed with his older sister.

Only after aggressively seeking a diagnosis did the couple, who live in Northern California, learn that Gregory had Type 3 Gaucher disease, which is associated with organ enlargement and seizures, and is rarer than the milder Type 1 form of the disease, which is more commonly tested for.

People with all forms of Gaucher disease lack an enzyme called glucocerebrosidase that helps the body eliminate dying cells. Those cells then accumulate in the body, swelling the liver, spleen, lungs, lymph system, bones and, in rare cases, the central nervous system or the brain.

For a child to get the disease, both parents must carry specific gene mutations. Scientists estimate that 6 to 10 per cent of Ashkenazi Jews are carriers of at least one mutation that can lead to Gaucher disease. Less than 1 per cent of the non-Jewish population are carriers.

"We were a one-in-a-million chance," Mr. Macres said. He and Ms. Macres are not of Jewish heritage.

Gregory died of complications from a bone-marrow transplant at 4. In the decade since, his parents have raised money to find a cure through their charity, Children's Gaucher Research Fund. They've also adopted three more children, unwilling to play the genetic lottery.

But Mr. Macres supports other parents who want to have themselves or their fetuses screened - particularly if they have a history of Gaucher disease in their family.

"Look, it's a life-altering event to have a child that has either a terminal disease or a very serious disease," Mr. Macres said. "So before people either get married or have children, maybe it's good that they know."

The new study tracked nearly 29,000 Israelis between 1995 and 2003. They opted to be screened for mutations in their DNA that could lead to Gaucher disease in their children.

The research team in Jerusalem interviewed 65 of the at-risk couples identified, who had a total of 90 pregnancies. In 68 of those pregnancies, parents opted to test for Gaucher in their fetuses. Sixteen of those fetuses screened positive. Of those pregnancies, four were terminated.

The researchers found that among couples who were counselled by a Gaucher expert and learned that the disease was treatable, only 8 per cent opted for abortion. All of the couples who didn't have counselling opted for abortion.

Realizing that more parents are going to grapple with these issues as genetic research marches forward, expert committees in North America and Israel are looking at which tests to recommend - or not.

The 2006 Ashkenazi screening guidelines of the Society of Obstetricians and Gynaecologists of Canada and the Canadian College of Medical Geneticists recommends against screening for Gaucher disease because it's rare to find severe forms, and most cases are treatable with enzyme replacement therapy.

The committee that drew up the guidelines also felt screening could cause mental distress, unnecessary medical testing and the abortion of healthy pregnancies, said Sylvie Langlois, a clinical geneticist and one of the lead authors of the committee's report.

"We recognized that over the coming years, there will be more and more testing that will be possible," said Dr. Langlois, an associate professor of medical genetics at the University of British Columbia.

"And the question is: If it is possible, should it be done?"