30 March 2011

All women should have cystic fibrosis screen

All pregnant women, as well as women who are planning a pregnancy, should be offered genetic screening for cystic fibrosis, experts have said.


All pregnant women, as well as women who are planning a pregnancy, should be offered genetic screening for cystic fibrosis, according to new guidelines from the American College of Obstetricians and Gynaecologists (ACOG).

In 2001, the ACOG recommended that screening for mutations in the CFTR gene be offered only to non-Hispanic white women, in part because cystic fibrosis is most common among Caucasians. The updated guidelines expand screening to women of all races and ethnicities.

At that point, little was known about the genetic defects that occur in people of other races and ethnicities, explained Dr William A. Hogge, chair of ACOG's Committee on Genetics, which updated the guidelines.

"Now we have a reasonable idea...of what those mutations are and how often they occur," he said.

Pre-pregnancy screening

In addition, he said, since many people are of mixed racial and ethnic backgrounds, it is reasonable to offer pre-pregnancy screening to all women.

No other medical groups have recommendations on pre-pregnancy or prenatal cystic fibrosis screening, Dr Hogge said. The US Preventive Services Task Force, an expert panel appointed by the federal government to review the scientific evidence on screening tests, hasn't issued any advisories on this issue, either.

Women do not have to undergo genetic testing before or during pregnancy. But they should be aware that it's available, Dr Hogge said.

Screening of newborns is routine, but that should not take the place of pre-pregnancy or prenatal screening, ACOG says. "We think it's better that women have all their options available to them before pregnancy."

Genetic counselling

If a woman has a positive result on pre-pregnancy testing, then her partner must be tested. If both appear to carry CFTR abnormalities, ACOG recommends that the couple have genetic counselling to discuss their options.

Caucasians have the highest rate of cystic fibrosis, at about one in 2,500 births. Overall, about 40 out of every 1,000 white people carry the gene defects that cause cystic fibrosis.

By comparison, Hispanic individuals have an estimated 17 in 1,000 chance of carrying the gene, African Americans a 16 in 1,000 chance, and Asian Americans a 10 in 1,000 chance.

People with cystic fibrosis are now living longer than in years past; but the typical life expectancy remains short, just 37 years.

Test not perfect

The basic test recommended for detecting CFTR abnormalities is not perfect. It screens for the 23 most common defects in the gene, but researchers have so far discovered more than 1,700 defects linked to cystic fibrosis.

So a negative result does not necessarily mean a woman is in the clear. And the test is less accurate for non-whites: after a negative result, whites still have a one-in-200 chance of being a carrier, while Asian Americans, for example, have a one-in-180 chance.

The screening test typically costs a few hundred dollars. Some research has suggested that the screening could be cost-effective, as people with cystic fibrosis need years of expensive medical treatment.

But the cost-effectiveness of offering screening to all women before pregnancy is not clear, according to Dr Hogge.

(Reuters Health, March 2011)

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