Causes and consequences of hyperhomocyst(e)inemia.

Increased plasma concentrations of the sulfur-containing amino acid homocyst(e)ine are designated as hyperhomocyst(e)inemia. Various definitions have been used to derive cut-off levels for hyperhomocyst(e)inemia. The classification by Kang is now generally used distinguishing moderate, intermediate and severe hyperhomocyst(e)inemia. A variety of causes are discussed for the etiology of the disease which can be grouped into genetic and nongenetic factors. Severe hyperhomocyst(e)inemia is accompanied by homocystinuria and several other symptoms occurring early in life. Treatment is mandatory for normal development and prevention of premature atherosclerosis. Even less severe forms of hyperhomocyst(e)inemia imply a substantially elevated risk for vascular diseases. Etiology and severity of defect(s) leading to hyperhomocyst(e)inemia are the basis for treatment. In genetic defects, supplementation with the cofactor(s) of the affected enzyme is used to enhance enzyme activity. Alternative routes in the pathway may also be enhanced. Nongenetic hyperhomocyst(e)inemia often requires correction of suboptimal vitamin concentrations. Nutritive doses of the vitamins may be sufficient for treatment of less severe forms as well as for prevention of hyperhomocyst(e)inemia.