The story of how these drugs came about began a decade ago. French researchers published a short note in the journal Nature Genetics reporting on three generations of a family with astonishingly high LDL levels — up to 466 — and a strong history of heart disease. Cholesterol, a yellow waxy substance that accumulates in clogged arteries, had piled up in their bodies. Some had cholesterol-laden nodules in their tendons that looked like bumps under the skin. The result was heart attacks, strokes and deaths from heart disease at an early age.

The cause of the family’s misfortune turned out to be a mutation in a gene called PCSK9, whose function was unknown.

Soon, researchers discovered that the gene slowed the body’s ability to rid itself of LDL. In the family studied by the French researchers, the mutated gene no longer worked properly and led to soaring cholesterol levels.

That gave Jonathan C. Cohen and Dr. Helen H. Hobbs of the University of Texas Southwestern Medical Center in Dallas an idea. If a mutation in PCSK9 leads to high LDL levels, perhaps there were defects that did the opposite — led to very low levels of LDL and protected against heart disease.

They found what they were looking for in data from a federal study. About 2.5 percent of blacks — but not whites — in the study had a single mutated PCSK9 gene that no longer functioned. About 3.2 percent of whites had a less powerful mutation that hampered the gene but did not destroy it.

Since people have two copies of every gene, one inherited from each parent, those with the newly discovered mutations did not have two mutated genes like the aerobics instructor, but instead had one fully functioning PCSK9 gene and one that was disabled. Still, the impact was clear. Blacks ended up with LDL levels that were 28 percent lower than normal, averaging 100 instead of 138. Whites with the less powerful mutation had LDL levels that were about 15 percent lower.

And significantly, people with one copy of a disabled gene had lower than normal LDL levels for their entire lives. That is very different from what happens when people start taking drugs to reduce their LDL levels in middle age, after heart disease has had decades to develop.