genetic tests in use in the UK detect D F508 plus up to
20 other mutations, which altogether account for 90% of
CF mutations in people of northern European origin. The
chance of detecting a mutation in both members of a
CF-carrier couple is thus about 80%. The specificity of
these tests is 100%, that is, any person who tests
positive will have the disease, although the severity
and course are less predictable.
If both partners in a couple are known CF carriers, they
can be offered antenatal genetic testing to determine
whether the foetus is affected. This genetic test is
virtually 100% accurate. Once a carrier is discovered in
a family, other family members can also be offered
testing, an approach known as cascade testing. An
information sheet is available.