It is preferable to start by testing patients in the family, if there are any. If
the gene is found using this method, other family members carrying the same mutation,
i.e. who are considered to be affected, can be identified. The fetus can also be
tested for the defect when one of the parents is affected, allowing for prenatal
diagnosis.
If a patient cannot be examined:
Family members, or a fetus, may be directly tested for the presence of the common
mutations, but the reliability of the test in such cases is reduced, depending on
the percentage of patients with these mutations in the particular ethnic group (degree
of coverage or percentage of detection of the mutations tested).
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