The genomes of any two people are more than 99% identical, but
seemingly minor variations between genomes contribute to each
individual’s risk for developing disease. By tracing the
inheritance of these genetic variants, scientists can discover
previously unsuspected genes as key players in the underlying
disease process. A recently completed catalog of common genetic
variation, known as the HapMap, has revolutionized human genetic
studies, making it possible for scientists to systematically
test common DNA variants for an association to disease risk.
This resource was genome-wide — that is, allowed testing of all
genes — and has made possible discovery in the last few years of
over 200 new genes that contribute to conditions such as
diabetes, elevated cholesterol levels, heart attack, rheumatoid
arthritis, lupus, Crohn’s disease, bipolar disease, and many
others. While successful, HapMap had a major limitation. It
contained only the most common genetic variants, those with
frequencies above 5% or so, and enc