2.2.3 Cystic fibrosis
A different model for the genetic tests of the future is screening for cystic fibrosis (CF). This is a DNA-based test, which became possible after the gene involved in CF was identified in 1989. CF is a recessive disease, and it should be easy to test to see if prospective parents carry a mutated allele. A simple mouthwash yields enough cells for DNA extraction. If both partners are carriers, they can consider further counselling before conception, and/or pre-natal testing of any potentially affected fetus.
Even simple disorders are turning out to be not so simple. There are now known to be more than 900 different mutations in the gene for CF. Many are rare, but even the best (and most expensive) testing currently envisaged would identify only about 85% of couples at risk. Even so, CF screening would probably be cost-effective, too. But the situation is complicated by the fact that the only way to ‘prevent’ the disorder is for two carriers to avoid having children, or to be prepared for an abortion if a pregnancy turns out to be the one in four that has two mutated copies of the gene for CF. At the same time, treatment for children with CF (Figure 3), more and more of whom now live well into adulthood, is getting better, but also more expensive. And prospective parents may, of course, hope that forecasts about gene therapy come true in time to help their child. So once again a potentially straightforward test leads to decisions that are anything but straightforward.