Applied to the study of the human genome, a goal of GWAS is to locate chromosome regions that are likely to contain genes influencing the risk of disease. Specific genes can be identified in these regions, and particular mutant alleles that increase disease risk can be sequenced. To date, the identification of alleles that increase disease risk has occasionally led to a new therapeutic strategy, but more often the identification of disease alleles is the only outcome.

What is the value of being able to identify alleles that increase disease risk for a person who is currently free of the disease but who is at risk of developing the disease due to its presence in the family?