A new poll shows parents are split over whether their newborns should be screened for fragile X syndrome, the most common type of inherited mental disability.

The findings fuel an ongoing debate over which conditions should be part of mandatory newborn screening programs in the U.S.

Fragile X syndrome, or FXS, brings the debate into sharp focus, because there is currently no cure for the condition. What’s more, not all kids with the gene mutation that causes FXS will have disabilities, so parents may end up worrying unnecessarily.

On the other hand, affected families may find it easier to prepare for their kids’ special needs if they know about them early on. Currently, FXS isn’t diagnosed until the child is at least three years old.

About one in 4,000 boys and one in 6,000 girls are born with the full mutation, which means they’re likely to have problems related to FXS. The disease is less common in girls because the gene is located on the X chromosome (the female sex chromosome).

For the new survey, published in the journal Pediatrics, researchers approached more than 2,000 new mothers at University of North Carolina Hospitals.

They asked the women and their partners if they wanted to have their newborn screened and to write down the reason for their answer.

Slightly less than two-thirds of the couples said yes, according to Debra Skinner of the University of North Carolina at Chapel Hill and colleagues.

Most of the mothers who accepted the test said they wanted to know about their child’s prospects, and the earlier the better. But many also said they agreed out of a wish to support research, hinting they might have misunderstood the purpose of the poll.

Of those who declined, about a fifth said they preferred not to worry about the results. A similar proportion said they didn’t like testing children or genetic testing in general, and somewhat fewer said they just didn’t want to know.

As one mother put it, “Knowing can cause anxiety. The chances of it happening are very small; don’t know how it will unfold. Not knowing will not make you treat your child a certain way.”

Black mothers were about half as likely as white or Hispanic mothers to want to screen their baby.

“This may be due to mistrust rising from the historical legacy of medical and genetic research in the United States with blacks,” the researchers write, “or to a different valuing of the benefits and risks of screening.”

The mandatory newborn screening program was first proposed by the American College of Medical Genetics in 2006. It included 29 “core” conditions, such as cystic fibrosis lung disease and phenylketonuria, a metabolic disorder that, untreated, leaves kids severely retarded.

But the group did not recommend screening for FXS, largely because the test was too expensive back then and didn’t lead to clear benefits.

However, the price has recently changed dramatically, plummeting from hundreds of dollars to less than $10 per test.

Yet experts say FXS is not like the conditions that are currently part of the newborn screening program, because it has no cure.

The test also identifies carriers of less-severe versions of the mutations, who might or might not develop problems, as well as people who don’t have noticeable symptoms despite harboring the full mutation.

In an editorial, Dr. Jeffrey Botkin of the University of Utah in Salt Lake City notes that “the potential benefits and risks associated with FXS screening are complex, subtle, and subjective.”

Instead of treating the condition as a public health problem that requires mandatory screening, he suggests screening for the disease might make more sense in the doctor’s office during well-child visits.

SOURCE: Pediatrics, online May 29, 2011.