U01.01.038 Marfan syndrome

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Learning Objectives

  • Identify the genetic mutation and inheritance pattern of Marfan Syndrome.
  • Recognize the multi-system involvement (skeletal, ocular, and cardiovascular).
  • Understand the role of Fibrillin-1 in elastin scaffolding and TGF-\beta signaling.
  • Master the high-yield clinical findings for USMLE preparation.

1. Genetics and Pathophysiology

Marfan syndrome is an autosomal dominant connective tissue disorder characterized by variable expression and pleiotropy (a single gene mutation affecting multiple, seemingly unrelated organ systems).

  • The Mutation: Defect in the FBN1 gene located on chromosome 15.
  • The Protein: Results in defective Fibrillin-1. This glycoprotein normally:
    1. Forms a structural sheath around elastin.
    2. Sequesters (limits the activity of) TGF- \beta
  • The Consequence: Weakened elastic fibers and excess TGF-\beta signaling lead to tissue overgrowth and structural fragility.

2. Clinical Findings

Symptoms are classically grouped into skeletal, ocular, and cardiovascular manifestations.

  • Skeletal:
    • Tall stature with long extremities (increased arm span-to-height ratio).
    • Pectus Deformities: Pectus carinatum (pigeon chest) or Pectus excavatum (sunken chest).
    • Arachnodactyly: Long, thin fingers and toes (positive “wrist” and “thumb” signs).
    • Hypermobile joints and scoliosis.
  • Ocular:
    • Ectopia lentis: Specifically, upward and temporal subluxation/dislocation of the lens.
  • Cardiovascular:
    • Mitral Valve Prolapse (MVP).
    • Cystic medial necrosis of the aorta.
    • Aortic root aneurysm, dissection, or rupture (the most common cause of death).
  • Other: Increased risk of spontaneous pneumothorax.

 

Activity

3. Clinical High-Yields

  • Mnemonic: Think of “Marfan fans OUT” to remember the upward/outward lens dislocation.
  • Management: Patients require regular echocardiograms. Beta-blockers or Angiotensin II Receptor Blockers (ARBs) like Losartan are used to reduce aortic wall stress and inhibit TGF-$Latex \beta$.

 

Activity