Plasma homocyst(e)ine as a risk factor for early familial coronary artery disease.

We measured plasma homocyst(e)ine [H(e)] and other coronary risk factors in 266 patients with early coronary artery disease from 170 families in which two or more siblings were affected and in 168 unmatched controls. The mean H(e) concentration adjusted for significant correlates (serum creatinine, uric acid, and low-density lipoprotein cholesterol) was 12.0 mumol/L in proband cases compared with 10.1 mumol/L in controls (P = 0.0001). Many (17.6%) of the proband cases had H(e) concentrations exceeding the 95th percentile for the controls (relative odds = 4.9, P < 0.001). H(e) among cases was bimodally distributed even after adjustment for concentrations of plasma vitamins. Concordant high H(e) was seen in at least 10 (12%) of 85 families with two or more affected siblings. We conclude that a substantial proportion of early familial coronary artery disease is probably related to production of high concentrations of H(e) by one or more major genes.