Marfan Syndrome

Slide 1 · Marfan syndrome

Molecular pathogenesis · Morphology · Clinicopathologic correlation

Fibrillin-1

Extracellular microfibrils

TGF-β

Signaling dysregulation

Aorta

Life-threatening injury

Dr Abu Suraih Sakhri

MBBS, MD (Pathology)

www.abusuraihsakhri.com

Slide 2 · Learning objectives

Explain FBN1-associated autosomal dominant disease

Distinguish structural and signaling mechanisms

Correlate the pathogenesis with organ-system findings

Recognize why aortic assessment is central

Organize every manifestation around the underlying extracellular-matrix defect.

Slide 3 · Marfan syndrome is a systemic connective-tissue disorder

Skeleton

Growth and ligament findings

Eyes

Lens-support abnormality

Cardiovascular

Aorta and cardiac valves

The skeleton, eyes, and cardiovascular system are prominently affected

A single molecular defect can produce disparate organ-level phenotypes

Aortic disease determines much of the life-threatening risk

Slide 4 · The multisystem pattern is more informative than body habitus alone

Systemic ECM defect

Variable organ involvement

Integrated assessment

Marked skeletal manifestations are not necessary in every affected patient

Cardiovascular or ocular manifestations may predominate

Clinical evaluation must not stop at tall stature

Schematic — causal sequence

Slide 5 · Aortic disease carries the greatest clinical hazard

Feature

Clinical interpretation

Valve manifestations

Often detectable; may produce regurgitation

Aortic involvement

Threatens the integrity of the arterial wall

Cardiac valve abnormalities may be frequent

The aortic complications are more clinically consequential

Slide 6 · Prevalence is approximately 1 in 5,000

This is the estimate reported by the source textbook

The condition is uncommon yet important as a cause of inherited aortopathy

The estimate describes population prevalence, not individual diagnostic probability

Epidemiologic prevalence cannot establish or exclude disease in an individual.

Slide 7 · Most cases are familial

Affected parent

Heterozygous transmission

Potentially affected offspring

Approximately 75% of cases are described as familial

Marfan syndrome follows autosomal dominant inheritance

Unaffected relatives do not exclude a de novo pathogenic variant

Schematic — causal sequence

Slide 8 · De novo FBN1 variants account for sporadic presentations

New pathogenic variant

Affected index patient

No preceding family phenotype required

The source attributes the remaining cases to new mutations

A negative reported family history is therefore not exclusionary

A patient with no affected parent can still have an inherited structural-protein disorder

Schematic — causal sequence

Slide 9 · Autosomal dominant transmission affects both sexes

Family-history concept

Implication

Vertical transmission

Supports autosomal dominant inheritance

No affected parent

Compatible with a de novo variant

Affected heterozygote

50% transmission risk per pregnancy

One heterozygous pathogenic variant can produce the phenotype

Both males and females can be affected and transmit the variant

Slide 10 · Connective tissue functions as an extracellular load-bearing system

Extracellular structural proteins

Resilience during stretch/recoil

Tissue integrity

Matrix proteins provide tensile support and resilience

Tissues exposed to stretching and recoil depend on intact fiber networks

A matrix defect may have both mechanical and signaling consequences

Schematic — causal sequence

Slide 11 · Fibrillin-1 is an extracellular microfibrillar glycoprotein

Fibrillin-1 molecules

Microfibril assemblies

ECM organization

Fibrillin-1 is a major constituent of matrix microfibrils

Microfibrils form organized assemblies in connective tissues

Abnormal fibrillin alters microfibril formation or abundance

Schematic — causal sequence

Slide 12 · Microfibrils provide the scaffold for elastic fibers

Microfibril scaffold

Tropoelastin deposition

Elastic-fiber network

Microfibril bundles are laid down in the extracellular matrix

Tropoelastin is deposited on that framework

The resulting elastic-fiber architecture supports deformability and recoil

Schematic — stages or conceptual sequence

Slide 13 · Elastic-fiber integrity matters most where tissues repeatedly stretch

Aorta

Cyclic vessel-wall strain

Ligaments

Joint stabilization

Zonules

Lens suspension

The aorta is exposed to pulsatile mechanical stress

Ligaments stabilize joints under movement

Ciliary zonules suspend the crystalline lens

Slide 14 · Fibrillin-1 and fibrillin-2 are distinct homologues

Gene

Protein

Source-linked disorder

FBN1

Fibrillin-1

Marfan syndrome

FBN2

Fibrillin-2

Congenital contractural arachnodactyly

FBN1 encodes fibrillin-1 on chromosome 15q21.1

FBN2 encodes fibrillin-2 on chromosome 5q23.31

Slide 15 · FBN1 is the principal Marfan syndrome locus

FBN1 variant

Altered fibrillin-1

Matrix dysfunction

Multisystem phenotype

Mutations in FBN1 are associated with the classic disorder

The encoded protein is part of the extracellular microfibril network

Gene–protein–matrix–organ relationships provide a unifying explanation

Schematic — causal sequence

Slide 16 · FBN1 variants are highly heterogeneous

Close to 1,000 distinct identified mutations

A single disorder arises from many different molecular alterations

Sequence heterogeneity contributes to phenotypic heterogeneity

Do not equate a single named variant with the entire clinical syndrome.

Slide 17 · Missense variants may exert dominant-negative effects

Missense FBN1 variant

Abnormal fibrillin-1

Impaired microfibril assembly

Weaker matrix

Abnormal fibrillin-1 can disrupt fiber polymerization

Mutant protein interferes with formation of a functional assembly

One altered allele therefore compromises matrix structure

Schematic — causal sequence

Slide 18 · Haploinsufficiency is a second mechanism

Reduced fibrillin-1 output

Subthreshold functional protein

Microfibril insufficiency

Some variants reduce effective fibrillin-1 abundance

The remaining allele does not supply sufficient functional protein

The source assigns approximately 10–15% of cases to this category

Schematic — causal sequence

Slide 19 · Dominant-negative and haploinsufficient defects differ

Feature

Dominant negative

Haploinsufficiency

Primary defect

Abnormal protein disrupts assembly

Insufficient functional protein

Common result

Compromised microfibrils

Compromised microfibrils

Both converge on reduced effective extracellular support

One mechanism disrupts assembly; The other lowers protein abundance

Slide 20 · FBN2-related disease is a useful molecular contrast

FBN2 variants are associated with congenital contractural arachnodactyly

It is described as an autosomal dominant skeletal condition

Similar fibrillin family membership does not imply identical phenotypes

The gene identity matters; Do not label every fibrillin-associated phenotype Marfan syndrome.

Slide 21 · Marfan pathogenesis has two converging mechanisms

Altered fibrillin-1

Weakened matrix support

Increased TGF-β signaling

Organ pathology

Loss of mechanical support in microfibril-rich matrix

Schematic — dual disease mechanisms

Slide 22 · Normal microfibrils mechanically reinforce connective tissue

Organized microfibrils

Elastic-fiber support

Resilient tissue

Fibrillin-rich assemblies integrate with elastic-fiber architecture

Elastic tissues withstand distortion and recover shape

Organ integrity depends on the organized extracellular network

Schematic — causal sequence

Slide 23 · Defective microfibrils weaken matrix-dependent tissues

Defective FBN1 product

Abnormal elastic scaffold

Loss of tissue support

Characteristic organ findings

Abnormal assembly disrupts the elastic-fiber framework

The aorta, ligaments, and lens zonules are particularly susceptible

Structural dysfunction explains several signature manifestations

Schematic — causal sequence

Slide 24 · Microfibrils also regulate TGF-β availability

Intact fibrillin-rich matrix

Extracellular TGF-β sequestration

Controlled growth-factor activity

Normal fibrillin-rich matrix sequesters TGF-β

Extracellular sequestration limits signaling availability

Microfibril dysfunction therefore perturbs growth-factor regulation

Schematic — causal sequence

Slide 25 · Altered fibrillin can increase TGF-β signaling

Microfibril defect

Reduced TGF-β sequestration

Excessive pathway activation

Reduced or abnormal microfibrils impair sequestration

More TGF-β becomes bioavailable to responsive cells

Growth-factor dysregulation is a second disease mechanism

Schematic — causal sequence

Slide 26 · Excessive TGF-β can disturb vascular smooth muscle biology

Excess TGF-β signaling

Abnormal smooth-muscle response

Vascular matrix vulnerability

The source links excess signaling to adverse smooth-muscle development

Altered cell–matrix interactions may impair vascular-wall homeostasis

This complements rather than replaces the structural explanation

Schematic — causal sequence

Slide 27 · Matrix metalloproteinases promote extracellular degradation

TGF-β overactivity

Higher MMP activity

ECM loss/remodeling

Further weakness

Excessive TGF-β signaling is linked to increased MMP activity

MMPs degrade extracellular-matrix components

Greater matrix turnover adds to structural weakness

Schematic — causal sequence

Slide 28 · TGF-β dysregulation explains features beyond reduced elasticity

Feature

Best emphasized pathway

Lens-zonule weakness

Structural support defect

Bone overgrowth

Signaling disturbance implicated

Myxoid valve change

Signaling disturbance implicated

Matrix weakness alone does not readily explain all disease effects

Bone overgrowth and myxoid mitral changes

Slide 29 · The two pathways are complementary rather than competing

Defective fibrillin-1

Mechanical support loss

TGF-β dysregulation

Combined tissue vulnerability

Mechanical effects weaken fibers and tissues

Schematic — dual disease mechanisms

Slide 30 · Related TGF-pathway variants can resemble Marfan aortopathy

The source describes disease associated with TGF-β type II receptor variants

It also describes TGFB3-associated inherited aortic predisposition

These observations support pathway involvement, not molecular identity with FBN1 disease

Distinct loci may converge on related aortic phenotypes; Preserve the genetic distinction.

Slide 31 · A single defect produces variable manifestations

Mechanical demand

Varies by organ

Signaling context

Varies by tissue

Molecular variant

Varies by patient

Different tissues depend on fibrillin-mediated support

TGF-β biology differs across the skeleton, valves, and vasculature

Mutation diversity contributes to variation among affected people

Slide 32 · Phenotypic variability is clinically important

Presentation

Important limitation

Striking body habitus

Does not prove ocular disease

Dominant ocular phenotype

May have few skeletal signs

Dominant cardiac phenotype

May have few skeletal signs

Some patients have striking skeletal changes

Others present with predominantly ocular or cardiovascular disease

Slide 33 · Skeletal manifestations are often the most visible

Body proportions

Long limbs and digits

Joint and spine

Laxity and curvature

Thorax

Anterior chest-wall deformity

The source identifies skeletal abnormalities as striking features

Typical findings concern height, proportions, joints, spine, and chest

They should be interpreted as part of a multisystem pattern

Slide 34 · Excess longitudinal growth alters body proportions

Many affected patients are unusually tall

Extremities can be disproportionately long

A tall body habitus is suggestive only in the right clinical context

Distinguish a characteristic habitus from a stand-alone diagnostic criterion.

Slide 35 · Arachnodactyly describes long, tapering digits

Altered skeletal growth

Long tapering digits

Arachnodactyly

Fingers and toes may be elongated and slender

This is a morphological description, not a specific genotype

Evaluate the finding alongside ocular and cardiovascular features

Schematic — causal sequence

Slide 36 · Ligamentous laxity contributes to abnormal joint movement

Weakened ligament support

Greater joint excursion

Hypermobility findings

The source describes lax ligaments in hands and feet

Some patients can hyperextend the thumb toward the wrist

Excessive mobility reflects reduced connective-tissue restraint

Schematic — causal sequence

Slide 37 · Craniofacial findings can support phenotype recognition

The source describes dolichocephaly

Frontal bossing and prominent supraorbital ridges are also described

These features are supplementary, not equivalent to aortic assessment

Craniofacial appearance is nonspecific without the systemic context.

Slide 38 · Spinal deformities reflect altered musculoskeletal support

Spinal change

Morphological description

Kyphosis

Excess sagittal curvature

Scoliosis

Lateral curvature

Rotational/slipping change

Altered vertebral alignment

Kyphosis and scoliosis can occur

Rotational or slipping changes of vertebrae are also described

Slide 39 · Chest-wall deformities are clinically recognizable

Deformity

Characteristic configuration

Pectus excavatum

Sunken anterior chest wall

Pectus carinatum

Protruding anterior chest wall

Pectus excavatum is a depressed-sternum deformity

Pectus carinatum produces anterior sternum prominence

Slide 40 · Skeletal findings do not predict the severity of aortic disease

Visible skeletal phenotype

Does not quantify aortic involvement

Separate cardiovascular assessment

Visible musculoskeletal changes may be extensive or subtle

The source emphasizes marked interpatient clinical variability

Cardiovascular assessment is necessary regardless of body habitus

Schematic — causal sequence

Slide 41 · Zonular weakness causes ectopia lentis

Zonular fibrillin defect

Loss of lens support

Ectopia lentis

The lens is suspended by circumferential ciliary zonules

Microfibrils are important for zonular tensile support

Weakening predisposes to lens subluxation or dislocation

Schematic — causal sequence

Slide 42 · Ectopia lentis is a particularly characteristic ocular finding

Dislocation or subluxation can be bilateral

Outward and upward displacement as typical

Bilateral ectopia lentis should prompt consideration of Marfan syndrome

The diagnostic implication lies in the distinctive ocular–systemic association.

Slide 43 · Lens displacement is a structural phenotype

Intact zonular support

Zonular weakness

Lens instability

Disrupted microfibrils weaken zonular attachments

The resulting mechanical instability displaces the crystalline lens

The ocular manifestation directly illustrates the support-defect pathway

Schematic — stages or conceptual sequence

Slide 44 · Aortic involvement is the major life-threatening manifestation

Weakened aortic matrix

Wall susceptibility

Dissection

Potential rupture

The aortic wall relies on elastic-fiber integrity

Extracellular-matrix dysregulation compromises vascular-wall resilience

Aortic dissection and rupture are the major feared outcomes described

Schematic — causal sequence

Slide 45 · Aortic dissection represents wall-layer separation

Aortic-wall weakness

Dissection

Possible rupture

The disease process involves compromised integrity of the aortic wall

Dissection creates a dangerous separation within the wall

Rupture of a dissection can cause catastrophic hemorrhage

Schematic — causal sequence

Slide 46 · Clinical priority follows the consequences, not frequency alone

Issue

Mitral involvement

Aortic involvement

Dominant consequence

Regurgitant valve dysfunction

Dissection and possible rupture

Priority

Function and symptoms

Life-threatening structural risk

Mitral lesions may be more frequent than some other abnormalities

Aortic lesions carry greater threat to life

Slide 47 · Loss of support makes mitral leaflets floppy

Mitral ECM support loss

Billowing / prolapse

Potential regurgitation

Matrix weakness produces soft, billowy leaflets

Mitral valve prolapse is a common cardiac finding

Changes may be accompanied by elongated chordae tendineae

Schematic — causal sequence

Slide 48 · Mitral valve prolapse may lead to regurgitation

Prolapse / chordal elongation

Imperfect closure

Mitral regurgitation

Abnormal leaflet movement interferes with normal closure

Chordal lengthening can aggravate impaired coaptation

Regurgitant flow is the major functional consequence described

Schematic — causal sequence

Slide 49 · Other cardiac valves may also be affected

Mitral valve

Frequent prolapse/regurgitation

Tricuspid valve

Similar changes possible

Aortic valve

Similar changes less common

The source reports similar changes in the tricuspid valve

Aortic valve involvement is described as rarer

Multivalvular findings reflect the systemic nature of matrix disease

Slide 50 · Echocardiography identifies cardiovascular manifestations

Suspected connective-tissue disease

Echocardiographic assessment

Document cardiac abnormalities

Its value in detecting cardiac abnormalities

Valvular structure and function can be assessed

Aortic and valve findings require direct evaluation rather than inference from appearance

Schematic — causal sequence

Slide 51 · Expression varies within and between families

Type of variability

Meaning

Intrafamilial

Different features among relatives

Interfamilial

Different patterns among families

Mutation heterogeneity

Plausible contributor to variation

The source describes variable manifestations within families

Differences between families may be more marked

Slide 52 · Absence of one organ-system sign cannot exclude disease

One positive clinical clue

Assess other affected systems

Avoid isolated-sign diagnosis

Ocular abnormalities may occur without a striking skeletal phenotype

Likewise, skeletal findings may be prominent without eye changes

The clinical assessment should deliberately survey multiple systems

Schematic — causal sequence

Slide 53 · Revised Ghent diagnosis integrates several evidence types

Family context

Inheritance history

Clinical findings

Aorta, lens and systemic signs

Molecular evidence

Relevant FBN1 variant

The source names family history, cardinal clinical features, and FBN1 status

Cardiovascular and ocular findings are particularly salient

The textbook excerpt is not a complete operational list of diagnostic rules

Slide 54 · A diagnostic assessment requires separate organ-system observations

Skeletal examination

Morphologic findings

Ophthalmic examination

Lens position

Cardiovascular assessment

Aortic and valve findings

Record skeletal features without equating them with diagnosis

Seek ocular features such as ectopia lentis

Determine cardiovascular abnormalities with appropriate clinical evaluation

Slide 55 · A gene result is interpreted alongside the phenotype

Observed FBN1 finding

Molecular interpretation

Multisystem phenotype correlation

FBN1 variants are diverse in molecular effect

The disease may involve dominant-negative action or haploinsufficiency

A molecular observation and a compatible clinical phenotype together are more informative

Schematic — causal sequence

Slide 56 · Marfan and Ehlers–Danlos syndromes target different matrix systems

Feature

Marfan syndrome

Ehlers–Danlos syndromes

Principal matrix defect

Fibrillin-1 / microfibrils

Collagen / collagen-related processes

Typical emphasis

Lens, skeleton and aorta

Skin, joints and tissue fragility

Marfan syndrome involves fibrillin-rich microfibrils

Ehlers–Danlos syndromes often involve collagen or collagen processing

Slide 57 · FBN2-associated contractural arachnodactyly is not Marfan syndrome

Disorder

Associated gene

Teaching distinction

Marfan syndrome

FBN1

Multisystem fibrillin-1 disorder

Congenital contractural arachnodactyly

FBN2

Related but distinct skeletal disorder

Both disorders affect proteins in the fibrillin family

The source assigns congenital contractural arachnodactyly to FBN2

Slide 58 · Case: Bilateral ectopia lentis with subtle skeletal changes

Finding: Bilateral ectopia lentis

A patient has bilateral lens displacement and few obvious skeletal signs

Which organ system must still be carefully assessed?

Answer: The cardiovascular system, particularly the aorta

Slide 59 · Case: Marked arachnodactyly without known family history

Finding: Skeletal pattern; No family history

A patient has long limbs, arachnodactyly, and chest-wall deformity

Does an unaffected family history rule out Marfan syndrome?

Answer: No; Sporadic de novo variants are described

Slide 60 · Case: Mitral prolapse should not end the evaluation

Finding: Mitral valve prolapse

A patient has mitral valve prolapse in a connective-tissue phenotype

What additional cardiovascular issue matters most?

Answer: Assess aortic involvement because of dissection risk

Slide 61 · Case: A genotype must be explained mechanistically

Molecular clue: Abnormal fibrillin-1 disrupts assembly

A variant produces abnormal fibrillin-1 that disrupts assembly

Which dominant molecular mechanism does this exemplify?

Answer: Dominant-negative interference with microfibril formation

Slide 62 · Mechanistic synthesis: Genotype to organ injury

FBN1-associated defect

Support failure

TGF-β excess

Multisystem clinical disease

FBN1 mutation produces abnormal quantity or quality of fibrillin-1

Schematic — dual disease mechanisms

Slide 63 · Clinical synthesis: Recognize and prioritize

Recognition

Eyes and skeletal pattern

Mechanism

Microfibrils and signaling

Priority

Aortic assessment

Ectopia lentis is a highly characteristic clue

Skeletal findings help recognize the phenotype but vary greatly

Aortic involvement is the central life-threatening concern

Slide 64 · References and source boundaries

Robbins, Cotran & Kumar: Pathologic Basis of Disease, 11th ed. (2026), Chapter 5, pp. 129–130

Adjacent parent context: “Autosomal Dominant Disorders,” Chapter 5

Adjacent Ehlers–Danlos section: comparison of extracellular-matrix disorders