Marfan syndrome

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Marfan Syndrome

Definition: Marfan syndrome (MFS; OMIM #154700) is an autosomal dominant disorder of fibrous connective tissue caused by mutations in the FBN1 gene, with primary manifestations in the skeletal, ocular, and cardiovascular systems.

Robbins & Kumar Basic Pathology, p. 110
Tietz Textbook of Laboratory Medicine, p. 2728

Genetics & Pathogenesis

Feature	Detail
Gene	FBN1 (fibrillin-1), chromosome 15q21.1
Inheritance	Autosomal dominant; ~70-85% familial, ~15-25% de novo
Prevalence	1 in 3,000-5,000 worldwide
Mechanism	Dominant negative effect - mutant fibrillin-1 disrupts normal microfibril assembly

Fibrillin-1 is a 320-kDa extracellular glycoprotein that self-assembles into 10-nm microfibrils, serving as the structural scaffold for elastic fibers in tissues like the aorta, ciliary zonules of the eye, and spinal ligaments. When fibrillin is defective, microfibrils fail, and - critically - sequestration of TGF-β is lost. Excess free TGF-β signals through the SMAD 2/3 and ERK pathways, causing:

Abnormal vascular smooth muscle development
Extracellular matrix degradation
Pathological bone overgrowth (explaining the tall stature)

Nearly 2,000 distinct FBN1 variants have been identified. Variants in exons 24-32 are associated with the severe neonatal form, earlier aortic dilation, ectopia lentis, and reduced life expectancy. - Tietz Textbook of Laboratory Medicine, pp. 2728-2729

A related syndrome, Marfan syndrome type 2 (MFS2), is caused by mutations in the TGF-β type II receptor gene (TGFBR2), confirming the central role of TGF-β signaling.

Clinical Features

Billy, who has Marfan syndrome, with characteristically disproportionately long arms (dolichostenomelia) and long fingers (arachnodactyly)

A young person with Marfan syndrome showing the characteristic long, disproportionate arms and slender build. - Thompson & Thompson Genetics, p. 526

1. Skeletal (most visible)

Tall stature, long limbs, arachnodactyly (spider fingers)
Arm span-to-height ratio > 1.05; reduced upper-to-lower body ratio
Pectus excavatum (funnel chest) or pectus carinatum (pigeon breast) - from rib overgrowth
Scoliosis in ~50% (progressive, can be severe)
High-arched, narrow palate with crowded teeth
Joint hypermobility and ligamentous laxity
Dolichocephaly, malar hypoplasia, micrognathia, retrognathia

2. Ocular

Ectopia lentis (bilateral lens subluxation) - present in ~60%; occurs superiorly/nasally; highly specific for MFS
Myopia (most common ocular feature)
Flat corneas
Increased risk: retinal detachment, glaucoma, cataracts (at younger ages)

3. Cardiovascular (most life-threatening)

Aortic root dilation - progressive; predisposes to aortic dissection and rupture
Cystic medionecrosis - fragmentation of elastic fibers in the tunica media
Aortic incompetence (dilation of aortic valve ring)
Mitral valve prolapse (floppy valve syndrome) - mitral regurgitation, congestive heart failure
Dilation of the proximal pulmonary artery

Aortic rupture is the most common cause of death, and can occur at any age.

4. Pulmonary

Spontaneous pneumothorax, apical blebs
Sleep apnea (secondary to skeletal deformities)
Scoliosis can impair pulmonary function

5. Neurological

Dural ectasia (dilation of the caudal thecal sac) in ~90% of patients - a major diagnostic criterion; worsens with age; can cause lumbar radiculopathy or CSF hypotension
Cardiogenic stroke risk (from prosthetic valves or atrial fibrillation)
Axonal neuropathy or mild myopathy
Intracranial vascular abnormalities (arterial dissections, giant aneurysms) - rare

6. Other

Striae atrophicae, recurrent hernias, lumbosacral dural ectasia
Flat feet

Bradley and Daroff's Neurology in Clinical Practice; Thompson & Thompson Genetics; Robbins & Kumar Basic Pathology

Diagnosis: Revised Ghent Nosology

Diagnosis requires one of the following combinations in a proband:

A pathogenic FBN1 variant + aortic root Z-score ≥2.0 OR ectopia lentis
Aortic root Z-score ≥2.0 AND ectopia lentis
Aortic root Z-score ≥2.0 + systemic score ≥7 (without ectopia lentis)
Ectopia lentis + an FBN1 variant known to be associated with aortic disease

Aortic root dilation and ectopia lentis carry the highest diagnostic weight given their relative specificity.

Molecular testing (DNA sequencing + deletion/duplication analysis) is not mandatory but is valuable in pediatric patients with incomplete phenotype, for family screening after an index variant is found, and for atypically mild presentations. Note: 7-30% of clinically diagnosed MFS patients have no detectable FBN1 variant by current methods.

Thompson & Thompson Genetics, p. 526; Tietz Textbook of Laboratory Medicine, p. 2729

Management

Management requires a multidisciplinary team: cardiologist, ophthalmologist, orthopedic surgeon, and medical geneticist.

Cardiovascular

Drug	Mechanism	Use
Beta-blockers	Lower heart rate and blood pressure; reduce aortic wall stress	First-line; slow aortic root dilation
Losartan (ARB)	Inhibits AT1 receptor; indirectly reduces TGF-β signaling	Adjunct to beta-blockers; may be more effective with haploinsufficiency variants
Statins / Tetracyclines	Inhibit MMP-2/MMP-9; reduce ECM degradation	Investigational
ERK inhibitors	Block ERK signaling downstream of TGF-β	Clinical trials ongoing

Prophylactic aortic root replacement is recommended when the aortic root reaches ≥5.5 cm in diameter
Annual transthoracic echocardiography for monitoring
Lifestyle modification: restrict to low-impact sports; avoid isometric exercise and contact sports

Ophthalmologic

Annual ophthalmologic evaluation
Surgical correction of ectopia lentis if vision is significantly impaired
Screen for glaucoma, cataracts, retinal detachment

Skeletal

Physical therapy and bracing for scoliosis
Surgical correction for severe scoliosis or pectus deformities when pulmonary function is compromised

Tietz Textbook of Laboratory Medicine, pp. 2729-2730; Robbins & Kumar Basic Pathology, p. 110

Prognosis

Without treatment, the average age of death was 32 years in the early 1970s. With modern cardiovascular surgical and medical management, life expectancy had already risen to ~72 years by 1993. Today, with proper management, life expectancy approximates that of the general population.

The most dangerous period is undiagnosed Marfan syndrome, where the first presentation may be sudden death from aortic dissection.

Thompson & Thompson Genetics, p. 526

Differential Diagnosis / Related Syndromes

Syndrome	Key Distinguishing Feature
Homocystinuria	Autosomal recessive; downward lens dislocation (vs. upward in MFS); intellectual disability; hypercoagulability/stroke risk; responds to B6/folate/B12
Loeys-Dietz Syndrome	TGFBR1/2 mutations; bifid uvula, hypertelorism, tortuous arteries; more aggressive aortic disease
MASS syndrome	Mitral valve, Aorta, Skin, Skeletal involvement without full MFS criteria
Ehlers-Danlos Syndrome	Collagen defects; skin hyperextensibility more prominent
Congenital contractural arachnodactyly	FBN2 mutation; joint contractures rather than hypermobility

Recent Evidence (2024-2026)

Recent systematic reviews are refining understanding:

Aortic biomechanical properties (stiffness, strain) may serve as early markers of aortic dilation before measurable dilation occurs [PMID: 39073692]
Thoracic aortic aneurysm growth rates meta-analysis (2025) provides updated data on predictors of aortic expansion [PMID: 40145320]
A 2025 systematic review highlights skeletal muscle alterations as a significant but underappreciated feature of MFS [PMID: 40833584]

These findings do not contradict the core diagnostic and management framework above, but suggest expanding surveillance to include vascular biomechanics and muscle assessment.

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