Marfan syndrome md pathology exam question Robbins based answer
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Marfan syndrome pathology FBN1 TGF beta Robbins overview
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Marfan Syndrome
Definition:
Marfan syndrome is an autosomal dominant connective-tissue disorder caused by mutations in FBN1, the gene encoding fibrillin-1. It predominantly affects the skeletal system, eyes, and cardiovascular system.
Marfan syndrome is an autosomal dominant connective-tissue disorder caused by mutations in FBN1, the gene encoding fibrillin-1. It predominantly affects the skeletal system, eyes, and cardiovascular system.
Etiopathogenesis
- Gene: FBN1 on chromosome 15q21.
- Protein defect: Fibrillin-1, an extracellular matrix glycoprotein produced by fibroblasts.
- Fibrillin forms microfibrils, which:
- Provide a scaffold for deposition of tropoelastin and elastic-fiber formation.
- Are especially abundant in the aorta, ligaments, and ciliary zonules of the lens.
- Normally sequester latent TGF-beta, restricting its activity.
Mechanism of disease:
- Mutant fibrillin has a dominant-negative effect, impairing normal microfibril assembly.
- Loss of functional microfibrils causes:
- Weak elastic connective tissue.
- Increased bioavailability and signaling of TGF-beta.
- Excess TGF-beta signaling contributes to abnormal extracellular matrix integrity, vascular smooth muscle dysfunction, and excessive skeletal growth.
About 70% to 85% of cases are familial; the rest result from de novo germline FBN1 mutations.
Morphology and Clinical Features
| System | Important findings |
|---|---|
| Skeletal | Tall, thin habitus; disproportionately long limbs and digits (arachnodactyly); high-arched palate; joint laxity; kyphoscoliosis; pectus excavatum or pectus carinatum |
| Eyes | Bilateral ectopia lentis due to weak ciliary zonules. This is a highly characteristic finding. |
| Cardiovascular | Aortic-root dilatation, aneurysm and dissection; aortic regurgitation; mitral valve prolapse due to floppy valves, possibly causing mitral regurgitation and heart failure |
Aortic Pathology
The aortic media shows:
- Fragmentation of elastic fibers
- Loss of medial structural support
- Classically termed cystic medial degeneration or cystic medionecrosis
Histologically, this includes smooth-muscle cell loss, elastic-tissue fragmentation, and proteoglycan-rich extracellular matrix accumulation. Despite the name, there are no true cysts.
The weakened aortic wall predisposes to aortic-root aneurysm and aortic dissection/rupture. These lesions are not exclusive to Marfan syndrome and may also occur with aging and hypertension.
Complications and Cause of Death
The most important and often fatal complication is:
Aortic dissection and rupture, usually secondary to progressive aortic-root dilatation.
Other major complications:
- Aortic valve-ring dilatation causing aortic incompetence
- Mitral valve prolapse and regurgitation
- Congestive cardiac failure
Diagnosis
Diagnosis is mainly clinical, supported by:
- Family history
- Characteristic skeletal, ocular, and cardiovascular findings
- Imaging of the aortic root
- Molecular testing for FBN1 mutations when required
Management Principle
Prevention of cardiovascular complications includes:
- Blood pressure and impulse reduction with beta-blockers
- Drugs that reduce TGF-beta signaling, including angiotensin receptor blockers in appropriate patients
- Serial aortic imaging and timely prophylactic aortic surgery when indicated
Robbins Exam Summary
Marfan syndrome is an autosomal dominant disorder due to mutation of FBN1 encoding fibrillin. Defective fibrillin causes abnormal microfibrils, defective elastic-fiber support, and excessive TGF-beta signaling. It presents with arachnodactyly, ectopia lentis, and cardiovascular lesions, especially aortic-root dilatation with cystic medial degeneration, aneurysm, dissection, and rupture.
Source: Robbins & Kumar Basic Pathology (Robbins Pathology), p. 110.
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