The test is performed on the patients themselves – even if there is only one. The
gene can be screened for a mutation without checking each and every one of its component
bases. This is a short, simple and more rapid test than establishing the entire
However, this method can identify only some mutations. If the defect is found using
this method, it is possible to determine who else in the family carries the mutation
and is therefore considered to be affected. The fetus can also be tested for the
defect if one of the parents is affected, allowing for prenatal diagnosis.
If a patient cannot be examined:
It is impractical (but possible) to check family members (or the fetus) directly
using the same methods, which are time-consuming and complex.