CLINICAL PHOTO — Marfan Syndrome Arachnodactyly + Long Limbs (FBN1)

A 28-year-old Indian man presents to cardiology clinic for evaluation of a family history of sudden cardiac death. On examination, he demonstrates the clinical features marked **A** in the diagram—tall stature with arm span exceeding height by 7%, long slender fingers with positive Steinberg and Walker-Murdoch signs, pectus excavatum, and generalized joint hypermobility. Echocardiography reveals aortic root dilatation at the sinuses of Valsalva. Genetic testing confirms a heterozygous mutation in the FBN1 gene on chromosome 15q21.1. Which of the following best explains the pathophysiologic mechanism linking the FBN1 mutation to aortic root dilatation in this patient?