FH is a codominant genetic disorder due to mutations in the gene for the LDL receptor. Plasma LDL levels are elevated at birth and remain so throughout life. In untreated heterozygous adults, total cholesterol levels range from 7.1 to 12.9 mmol/L (275-500 mg/dL). Plasma triglyceride levels are typically normal, and HDL cholesterol levels are normal or reduced. Heterozygotes, especially men, are prone to accelerated atherosclerosis and premature coronary artery disease (CAD). Tendon xanthomas (most commonly of the Achilles tendons and the extensor tendons of the knuckles), tuberous xanthomas (softer, painless nodules on the ankles and buttocks), and xanthelasmas (deposits on the eyelids) are common. In its homozygous form, FH leads to severe atherosclerosis during childhood.