Symptoms Adults and children who have familial hypercholesterolemia have very high levels of low-density lipoprotein (LDL) cholesterol in their blood. LDL cholesterol is known as "bad" cholesterol because it can build up in the walls of the arteries, making them hard and narrow. The body needs some cholesterol to build healthy cells. But high cholesterol can raise the risk of heart disease. Lifestyle changes can help. If there's too much cholesterol in the blood, the cholesterol and other substances may form deposits called plaque. Plaque can cause an artery to become narrowed or blocked. Atherosclerosis symptoms usually don't happen until an artery is so narrowed or clogged that it can't send enough blood to organs and tissues. Sometimes a blood clot completely blocks blood flow.
