Apolipoprotein (apo) A-I is the major apolipoprotein of HDL and is a single polypeptide chain with 243 amino acid residues. Familial apo A-I deficiency is a rare metabolic disorder of which 13 cases have been characterized at the molecular level. However, in subjects with apo A-I deficiency, coronary artery disease is not always present. To date, more than 40 genetically determined structural variants of apo A-I have been identified. Seven apo A-I mutations have been identified to cause hereditary amyloidosis. In our laboratory, we characterized ten apo A-I variants, including apo A-I(Vall56Glu) Oita. A minority of structural variants were associated with altered HDL cholesterol levels or increased risk for cardiovascular disease.