Gene test results may be misinterpreted
Antenatal genetic screening for cystic fibrosis could have led to unnecessary and risky tests during pregnancy, and even abortions, it has been claimed.
Two years ago, the US introduced a national screening programme for cystic fibrosis (CF), where any pregnant woman can request that they and their partners are checked.
But geneticists warn the results may have been misinterpreted and some women may have undergone unnecessary amniocentesis tests, which can result in miscarriage.
Some may even have had an abortion, New Scientist magazine reports.
These findings are a frightening warning of the complexities and dangers of genetic screening
Dr Helen Wallace, GeneWatch UK
In the UK, Scotland offers CF testing for all newborn babies. The government has also pledged to introduce the tests in England.
There are currently no plans for a national antenatal genetic screening programme to be introduced.
But experts say the same problems would be unlikely to happen in the UK because of the high standard of laboratories and genetic counselling services across the country.
Under the US screening system, parents' blood and saliva is tested to see if they carry any of the genetic mutations which contribute to CF.
If both are carriers, there is a one in four chance they will have a child with CF.
A DNA test is then carried out on the fetus. If it has inherited two defective copies of the CF gene and is likely to develop the disease, couples have to decide if they want to continue with the pregnancy.
Around 900 mutations in the CF gene, or the DNA surrounding it can cause some, or all, symptoms of the condition, but commercial tests only look for the most common 25 to 35 mutations.
One is called 5T, but it only contributes to CF if the rarer R117H mutation is also present in the same gene.
But representatives from the American College of Medical Genetics told a US conference this year that over 20 prenatal tests had been carried out on fetuses when parents carried only 5T, and terminations had occurred.
The ACMGs executive director Michael Watson told New Scientist magazine he knew of "at least 150 prenatals that have been done that perhaps should not have been done".
He said the increase in tests may have led to laboratories making mistakes.
Dr Watson said: "The volume of tests has exploded, and front-line service providers are having some difficulty with the hard mutations that are difficult to interpret."
Charles Strom is medical director of genetics at Quest Diagnostics in California, which has seen several fetal samples where the 5T mutation was the only reason for having the amniocentesis, contrary to US gene test rules.
He warned: "This is not a unique situation. I think you can say with some certainty that this is going on throughout the industry."
He said doctors may order the wrong tests, genetic counsellors may misinterpret the parental 5T tests, or parents become over-anxious and request a fetal test anyway.
Dr Jim Littlewood told BBC News Online: "One of the things about having a test like this is that it has to be accompanied by genetic counselling."
He said the UK had a very good laboratory network and genetic counselling service, but warned a national screening programme would be very expensive, costing up to £100,000 to identify one baby affected by CF.
He said the US did not have the same kind of lab network or counselling services. "It doesn't surprise me that they've got into a tangle in the US."
'More harm than good'
Dr Helen Wallace of GeneWatch UK said: "These findings are a frightening warning of the complexities and dangers of genetic screening.
"Testing can be helpful for some couples, but screening every pregnant woman can do more harm than good.
"More genetic screening means more profits for genetic testing companies - this must not take priority over warning women of the dangers of these tests. Even if guidelines are strictly followed, genetic tests will never accurately predict your child's future quality of life. "
CF affects around 7,500 people in the UK. It causes the lungs to produce too much mucus, and prevents the body from digesting fat. Many people with CF can live into middle age.