One of the chief arguments advanced by those against such screening is that currently available tests can identify primarily those with the most common CF mutation--the F508 mutation, which the Cystic Fibrosis Foundation estimates accounts for about 70 percent of all CF carriers. They can also identify a handful of other, far less common mutations, occurring in the rest of CF carriers. Because tests can't identify 100 percent of all CF mutations, the tests may do more harm than good, opponents say. For example, at 80 percent sensitivity, the tests will identify perhaps 64 percent of the couples at risk of having children with CF. Meanwhile, other couples--especially those in which one partner tests positive for the F508 and the other tests negative for all known mutations--will be left with uncertainties that some in the research community believe outweigh the potential benefits to the relatively few carrier-carrier couples identified.
But ...
