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 to decide whether to have children.
Births of babies with cystic fibrosis, Tay-Sachs and other less familiar disorders have dropped since testing came into wider use, The Associated Press found from a review of studies and interviews with numerous geneticists and other experts.
Many of these diseases are little known, and few statistics are kept. But their effects -- ranging from blood disorders to muscle decline -- can be disabling and often fatal during childhood.
Now, more women are being tested as part of routine prenatal care, and many end pregnancies when diseases are found. One study in California found that prenatal screening reduced by half the number of babies born with the severest form of cystic fibrosis because many parents chose abortion.
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.
The cost of testing is falling, and the number of companies offering it is rising. A 2008 federal law banning gene-based discrimination by insurers and employers has eased fears.
Genetic testing pushes hot-button issues: abortion, embryo destruction and worries about eugenics, selective breeding to rid a population of unwanted traits.
Although genetic testing can raise moral dilemmas, at least one conservative religious group -- Orthodox Jews -- has found ethically acceptable ways to use it to lessen diseases that have plagued its populations.
"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. The genes can pass quietly for generations until two carriers mate; then children have a 1-in-4 chance of getting the disease.
Statistics for inherited diseases are hard to come by -- birth certificates often don't list them, and they sometimes aren't diagnosed for months or years after birth. 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, or Eastern European 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 Kaback, a professor at the University of California at San Diego who tracks the disease.
Another disease on the decline 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, floppy muscles, digestive and other problems, and kills many by young adulthood.
Lots of eyes are on cystic fibrosis, a disease that causes sticky mucus buildup in the lungs, digestive problems and death in young adulthood. More than 10 million Americans -- 1 in 25 to 29 whites, who are more at risk for it 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, as did 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 10 in 2003, ticking up to 15 in 2006, said Dr. Richard Parad, a Brigham and Women's Hospital physician who helped set up the screening program.
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.
Newborn screening is finding more sickle cell carriers and cases, but this doesn't seem to affect parents' future family plans, said Dr. Lanetta Jordan, chief medical officer of the Sickle Cell Disease Association of America.