How well each person controls his or her level of blood cholesterol is heavily influenced by genes.

Those with the worst problem, however, have familial hypercholesterolemia, a genetic disorder that causes them to make abnormally high levels of cholesterol. The most common form of the disease, caused by inheriting one of a pair of mutant genes, strikes one out of every 500 individuals. A more lethal form occurs when a person inherits both copies of the defective gene pair, about once in every million births.

"If you find a young man who has had a heart attack, and you find he has familial hypercholesterolemia . . . half of his children will have it. Half of his brothers and sisters will have it," said Dr. Basil Rifkind, chief of lipid metabolism at the National Heart Lung and Blood Institute. "Hopefully, we will find it before they run into trouble."

The defective gene controls the production of a receptor for low-density lipoprotein (LDL), a form of cholesterol. Receptors are proteins on the surface of cells that recognize various chemicals and then cause some biological response.

Normally, receptors on liver cells remove excess LDL from the blood. But if the cells lack LDL receptors, or there is something wrong with them, LDL blood levels rise uncontrollably.

An individual who inherits one defective LDL gene tends to make only half of the normal number of LDL receptors; those inheriting two defective LDL genes make almost no functioning receptors.

Typically, a person with one defective gene has cholesterol levels of 300 to 500 milligrams of cholesterol per deciliter of blood. For those who inherit both of the bad genes, cholesterol levels can range from 600 to 1,000. The recommended level for adults is 200.

Adults with one defective gene can begin having heart attacks in their thirties. Those with both defective genes begin having heart attacks as early as their second birthday and most have had at least one by their twenties.

"These children are devastated," Rifkind said.

Unfortunately, this condition is very difficult to treat, he said. "All of them {people with the disease} should be on a cholesterol-lowering diet and later will probably need drugs."

One child appears to have been cured when she received a liver transplant at the same time as a heart transplant -- her heart had been so wracked by heart attacks that she was dying. The new liver carried normal LDL receptors which cause it to pull cholesterol out of her blood. Her cholesterol levels dropped dramatically -- from nearly 900 to about 300. So far, she continues to do well.