To the Editor.
—We would like to give a brief report on mitral valve prolapse syndrome (MVPS) in identical male twins in whom intraventricular conduction defects developed and whose father had asymmetric septal hypertrophy.
Report of Cases.—Case 1.
—An asymptomatic 13-year-old boy was referred to the cardiology clinic because of a cardiac murmur disclosed on a routine physical examination. His stature was normal, the apical cardiac impulse was palpable in the normal position, and a 1/6 short systolic murmur and a variable systolic click were audible, which were not modified by upright position. No other physical abnormality was evident. The resting ECG was unremarkable. After exercise stress test (150 W), ventricular extrasystoles were observed. Chest roentgenograms were normal. The echocardiogram demonstrated prolapse of the posterior mitral leaflet. During a three-year follow-up period, serial ECG tracings demonstrated gradual development of an intraventricular conduction defect (QRS complex, 0.12 s) and