Familial hypercholesterolemia: The most common inherited type of hyperlipidemia (high lipid levels in the blood). Familial hypercholesterolemia is recognizable in childhood and is due to genetic defects in the receptor (target) for low-density lipoprotein (LDL). The most common autosomal dominant form of hypercholesterolemia is caused by mutation in the LDL receptor gene (LDLR) on chromosome 19. There are also a number of other less frequent forms of this disorder. Familial hypercholesterolemia predisposes a person to premature arteriosclerosis, including coronary artery disease, and can lead to heart attacks at an unusually young age. Treatment involves dietary modifications and the use of cholesterol-lowering medications.