If a deleterious (also called pathogenic) gene mutation is identified in a family, the individual family members typically are tested for only the mutation that was found. Testing for the known familial mutation is called single-site testing. Most insurance companies will cover single-site testing, which typically costs $200 to $500.
It’s important to carefully evaluate a person's family history when undertaking single-site testing. Clinicians should consider the possibility that the patient may have a risk for a different mutation from the other side of his or her family.
Different laboratories may use different primers for sequencing. It is possible that a family may have a unique sequence variation that may occur near the location where a specific primer binds. This could potentially cause a laboratory to not be able to detect a mutation that is present in that family, even if the laboratory has detected the same mutation in other families. For this reason, it’s important to perform single-site testing at the same laboratory where the mutation was found in a family member. If this is not possible, a sample from a family member who is known to have the familial mutation should be sent in with the patient's specimen to confirm that the laboratory is able to detect the mutation in that family.
Single-site testing for moderate penetrance gene mutations may not be the only appropriate testing for family members. Given the lack of data on potential multiple germline gene mutations in families with hereditary cancers, full gene or further panel testing may still be recommended, particularly for affected family members.