Background Mitral valve prolapse syndrome (MVPS), a term applied to patients who have a variety of symptoms, has been associated with autonomic or neuroendocrine dysfunction. Recent evidence suggests that effects of angiotensin II mediated by the angiotensin II type 1 (AT₁) receptor are involved in modulation of cardiovascular autonomic control in human beings. Association of a genetic polymorphism (A-C¹¹⁶⁶) of the AT₁ gene with abnormal vasomotion and low blood pressure related to autonomic control has been reported recently. Because the role of this genetic variant in MVPS has not been studied, we performed a case-control study of the A-C¹¹⁶⁶ variant in a group of 76 white subjects with MVPS. Methods and Results All patients were genotyped by use of a mismatch polymerase chain reaction/Afl II restriction fragment length polymorphism analysis. Frequency of the C¹¹⁶⁶ allele was 0.4 in patients with MVPS and 0.26 in control patients. The difference in genotype (chi square = 6.5; P < .05) and allele (chi square = 5.9; P = .02) frequencies between the groups was significant. The odds ratio in favor of carrying the C allele was 4 times greater for patients with MVP than for control patients (95% confidence interval 1.4 to 12.1). Conclusions The current results indicate that the A-C¹¹⁶⁶ polymorphism of the angiotensin II type 1 receptor gene is associated with MVPS in the white population. (Am Heart J 2000;139:101-5.)