A 22-year-old man has a sudden loss of vision in the right eye. On physical examination, there is a subluxation of the right crystalline lens. On auscultation of the chest, a midsystolic click is audible. An echocardiogram shows a floppy mitral valve and dilated aortic arch. The patient's brother and his cousin are similarly affected. He is prescribed a beta-blocker. A genetic defect involving which of the following substances is most likely to be present in this patient?
High-Yield Explanation
Marfan syndrome is an autosomal dominant condition that is most often caused by qualitative defects in fibrillin from missense mutations in the fibrillin (FBN1) gene. An abnormal collagen gene can cause osteogenesis imperfecta and Ehlers-Danlos syndrome. Genetic mutations in the dystrophin gene are involved in Duchenne and Becker muscular dystrophies. The NF1 protein is abnormal in neurofibromatosis type 1. Disordered spectrin causes hereditary spherocytosis.