Which statement best describes cascade testing and its efficiency for identifying at‑risk relatives?

• A. Testing all relatives at once regardless of risk.
• B. Testing unrelated individuals with the same condition.
• C. Sequential testing of relatives starting with first‑degree relatives.
• D. Testing only the proband.

Answer: (C)

Cascade testing is a stepwise approach to identify at‑risk relatives by using what is already known from the family. Once a pathogenic variant is found in the proband, you test relatives who are most likely to carry it first—starting with first‑degree relatives (parents, siblings, and children) because they share about half of their genetic material and have the highest probability of carrying the same variant. If a relative is found to have the variant, the testing circle continues to their first‑degree relatives, and so on, in a logical, sequential way. This minimizes unnecessary tests and focuses resources on those with the highest chance of being affected or at risk, while providing timely information for surveillance or preventive steps.

Testing all relatives at once is inefficient and costly, testing unrelated individuals with the same condition ignores the familial link and the specific inherited variant, and testing only the proband stops the cascade before informing other at‑risk relatives.