Some of mankind's most devastating inherited diseases appear to be declining, and a few have nearly disappeared, because more people are using genetic testing before having children.
Births of babies with cystic fibrosis, Tay-Sachs and other less familiar disorders have dropped since testing came into wider use, according to numerous experts and a review of the limited research available.
Some of these diseases are little known and few statistics are kept. But their effects can be often fatal during childhood.
Now, more women are being tested as part of routine prenatal care, and many end pregnancies when diseases are found. More couples with no family history of inherited diseases are getting tested before starting families to see if they carry mutations that put a baby at risk. And a growing number are screening embryos and using only those without problem genes.
A proactive approach
Genetic testing pushes hot-button issues: abortion, embryo destruction and worries about eugenics, or selective breeding. Yet it touches many, such as:
• In suburban Cleveland, Beth and Thad Meese were stunned to learn during her second pregnancy that they carry genes that can cause cystic fibrosis. Tests show the baby won't have the disease, but they have decided against having a third child or to screen embryos if they do. "I feel like we got lucky," she said.
• In Boston, Harvard psychologist and author Steven Pinker and his wife, novelist Rebecca Goldstein, learned last year that they carry genes that cause a serious neurological disease, familial dysautonomia. Too old to have children, they shared the news with younger relatives, who are being tested to see if they, too, have the gene.
• In Vancouver, British Columbia, Jeff and Megan Carroll screened embryos to have two children free of the Huntington's disease gene Jeff has. Huntington's "is done killing people in my family when I am gone," he said.
Rabbi: It's not eugenics
Genetic testing can raise moral dilemmas, but at least one conservative religious group — Orthodox Jews — has found ethically acceptable ways to use it.
"I am a Holocaust survivor. I was born in the middle of the second World War. I hope that I am not a suspect for practicing eugenics. We are trying to have healthy children," said Rabbi Josef Ekstein of New York, who founded a group that tests couples and discourages matches when both carry problem genes.
Some diseases — sickle cell, cystic fibrosis, Tay-Sachs, thalassemia, spinal muscle atrophy — occur when people inherit two bad genes, one from each parent.
(Down syndrome is the best known disorder for which prenatal testing has long been available, but it's caused by an extra chromosome during abnormal cell division — not genes inherited from the parents.)
Statistics for inherited diseases are hard to come by. Yet, there's little doubt that testing has put a dent in many.
"We're definitely seeing decreased rates of certain genetic disorders as a result of carrier screening," said Dr. Wendy Chung, clinical genetics chief at Columbia University. In five years, she has seen only one case of Tay-Sachs, a neurological disease that used to be more common in Ashkenazi Jews. Children with the disease lack a key enzyme; they lose mental and physical abilities and usually die by age 4.
In the last decade, only about a dozen new cases of Tay-Sachs occurred each year in the United States, said Dr. Michael Kuback, a professor at the University of California at San Diego who tracks the disease.
Ekstein, the rabbi, lost four children to it before founding Dor Yeshorim, a Brooklyn group that recruits Jews to be tested before marriage. The group has 300,000 members and tests for nine diseases, including cystic fibrosis.
"In the Orthodox Ashkenazi community around the world, we virtually have wiped out the diseases we screen for," said the group's development director, Allan Binder.
One is familial dysautonomia. Since 2004, only a few children worldwide have been born with it each year, and it soon may cease to exist because of genetic screening, said Dr. Barron Lerner, a Columbia University medical historian. The disease causes faulty nerve development and other problems, killing many by young adulthood.
Fragile X syndrome, the leading cause of mental impairment in boys, may decline because carrier and prenatal testing of fetuses is now available for it, said Barbara Biesecker, director of the genetic counseling program at the National Institutes of Health.
Lots of eyes are on cystic fibrosis, which causes sticky mucus buildup in the lungs, digestive problems and death by young adulthood. More than 10 million Americans — whites are more at risk than blacks — carry a gene mutation for it. In 2001, the American College of Obstetricians and Gynecologists and other groups recommended that white pregnant women be offered testing for mutations. Tests on partners and fetuses often followed, and an unknown number of abortions.
The impact showed up two years later in Massachusetts, one of the few states testing newborns for the disease at the time. Births of babies with cystic fibrosis dropped, from 29 in 2000 to only 10 in 2003, ticking up to 15 in 2006, said Dr. Richard Parad, a Brigham & Women's Hospital physician who helped set up the screening program.
In California, Kaiser Permanente, a large health maintenance organization, offered prenatal screening. From 2006 through 2008, 87 couples with cystic fibrosis mutations agreed to have fetuses tested, and most found to have the disease were aborted. Studies in Canada, Italy, Australia and in Europe also found that cases dropped after screening began.
The Cystic Fibrosis Foundation's registry shows a steady rise in recent years. But that is because more states have started testing all newborns, discovering cases that previously went unreported, some researchers believe.
Not always effective
Gene testing hasn't led to declines in all diseases. Sickle cell, a blood disorder that causes anemia and pain, and raises the risk of stroke, has not dropped. It mostly afflicts blacks; gene carriers are said to have sickle cell "trait," which sounds harmless.
"Now we're actually learning that it's not as benign as we thought it was," and that carriers have higher risks for certain medical problems, said Dr. Lanetta Jordan, a Broward County physician and chief medical officer of the Sickle Cell Disease Association of America.
Gene testing also has had little impact on Huntington's disease, a progressive, fatal neurological disorder. Unlike many other inherited diseases, only one bad copy of a gene is needed to cause Huntington's, and symptoms don't usually appear until middle age, after many have already had children.