A 33-year-old woman delivers a healthy neonate at 38 weeks gestation. Two days later, the mother collapses in the nursery. Examination of medical records shows that the patient's father died at age 45 due to complications of Marfan syndrome. Blood pressure is 110/50 mmHg and pulses are diminished, Cardiac auscultation reveals a diastolic murmur. Which of the following is the most likely diagnosis?