Which statement about distinguishing targeted mutation testing from diagnostic sequencing is correct?

• A. Targeted mutation testing expands to genome wide coverage and is not limited to known variants.
• B. Targeted testing is only applicable when phenotype clearly points to a single gene.
• C. Targeted testing identifies all possible genetic variants in the genome.
• D. Targeted testing is indicated when a known familial variant has been previously identified.

Answer: (D)

Targeted mutation testing is designed when a specific familial variant has already been found in a relative. In this approach, you test for that exact variant in other family members to determine who carries it or is at risk, which makes the test fast, inexpensive, and focused with fewer incidental findings. Diagnostic sequencing, in contrast, surveys larger regions (like a gene panel, exome, or genome) to identify any pathogenic variant, including novel ones, when the causative variant isn’t already known. The other statements describe broader sequencing concepts rather than the focused purpose of targeted testing. Therefore, testing for a known familial variant identified previously is the appropriate indication for targeted testing.