Surfactant Dysfunction Disorders

Slide 1 · Surfactant dysfunction disorders

Inherited abnormalities of surfactant transport, secretion and protein function

Genetics • Alveolar pathology • Clinical spectrum

Dr Abu Suraih Sakhri

MBBS, MD (Pathology)

www.abusuraihsakhri.com

Slide 2 · Learning objectives

Link surfactant biology to alveolar stability and respiratory failure.

Compare the ABCA3, SFTPC and SFTPB disease groups.

Recognize the distinctive light-microscopic, immunohistochemical and ultrastructural findings.

Distinguish surfactant dysfunction from premature-infant RDS and alveolar proteinosis.

Slide 3 · One disease family, several clinical entry points

Respiratory failure

Soon after birth

Progressive disease

In infancy

Childhood

Interstitial lung disease

Adult-onset

Interstitial lung disease

Age at presentation is informative, but it does not uniquely identify the gene.

Slide 4 · Definition: Inherited disturbance of surfactant handling

Mutations affect proteins involved in surfactant trafficking or secretion.

The common target tissue is the alveolar epithelial system.

The result is a spectrum of alveolar and interstitial lung injury.

Genetic mechanism is distinct from surfactant accumulation caused by defective macrophage clearance.

Slide 5 · The alveolar epithelial unit

Alveolar airspace

Type I cell: Thin gas-exchange surface

Type II cell: Synthesizes surfactant; Supports repair

Slide 6 · Type II pneumocytes are central to these disorders

Normal physiologic roles

Synthesize alveolar surfactant

Participate in epithelial repair

Contain surfactant-related lamellar bodies

Disease-associated changes

Abnormal lamellar bodies

Type II pneumocyte hyperplasia

Variable alveolar/interstitial injury

Slide 7 · Surfactant contains lipids and specialized proteins

Component

Role stated in Robbins

Dipalmitoyl phosphatidylcholine

Major surfactant phospholipid

Phosphatidylglycerol

Additional phospholipid component

SP-A and SP-D

Hydrophilic proteins contributing to innate host defense

SP-B and SP-C

Hydrophobic proteins supporting reduction of surface tension

Slide 8 · Surfactant reduces surface tension at the air–liquid barrier

Surfactant lipids

+ SP-B / SP-C

Lower alveolar

Surface tension

Less pressure needed

To maintain patency

Stable air-containing

Alveoli

Mechanistic connection: Surface tension determines the work required to reopen alveoli.

Slide 9 · Loss of effective surfactant increases work of breathing

Adequate surface activity

Reduced surface activity

Lower opening pressure

Repeated collapse; Greater effort

Schematic — depicts physiologic direction, not alveolar measurement

Slide 10 · Surfactant homeostasis requires production and clearance

Type II pneumocyte

Synthesis

Transport, storage

And secretion

Surfactant at the

Alveolar interface

Clearance by

Alveolar macrophages

The inherited dysfunctions primarily involve epithelial surfactant handling; PAP primarily involves clearance.

Slide 11 · Two mechanistic routes to abnormal surfactant balance

Epithelial surfactant dysfunction

Mutant surfactant protein or trafficking component

Abnormal lamellar bodies may develop

Interstitial and alveolar damage may coexist

Alveolar proteinosis (PAP)

Impaired macrophage-dependent catabolism

Surfactant accumulates in airspaces

Lamellar bodies typically remain normal

Disease mechanisms overlap in airspace material but differ in the primary affected process.

Slide 12 · The genotype–phenotype relationship is heterogeneous

All three gene groups are associated with surfactant dysfunction.

The most severe disease may present as early respiratory failure.

A chronic interstitial lung disease phenotype can be recognized later in life.

Age, microscopic appearance and a family history provide clues rather than a unique genotype.

Slide 13 · Principal genes in the Robbins account

Gene / protein

Relative frequency

Inheritance

ABCA3

Most commonly mutated

Autosomal recessive

SFTPC / surfactant protein C

Second most common

Autosomal dominant

SFTPB / surfactant protein B

Third most common

Autosomal recessive

Frequency is a textbook ranking, not a population-specific estimate.

Slide 14 · Each gene disrupts the surfactant system differently

ABCA3

Lipid transport

SFTPC

Protein C pathway

SFTPB

Protein B pathway

Different molecular starting points converge on abnormal alveolar surfactant biology.

Slide 15 · ABCA3: Membrane-associated lipid transport

ABCA3 encodes an ATP-binding cassette transporter.

The protein is transmembrane and participates in lipid transport.

Its activity contributes to surfactant homeostasis.

Loss of normal function is associated with abnormal type II-cell lamellar bodies.

Slide 16 · ABCA3 links lipid trafficking to lamellar-body biology

ABCA3 protein

In type II cell

Regulated lipid

Transport

Normal surfactant

Homeostasis

Functional alveolar

Surfactant

Disruption of the transporter is associated with an abnormal lamellar-body ultrastructure.

Slide 17 · ABCA3-associated disease is autosomal recessive

Inheritance pattern

Autosomal recessive transmission

Both gene copies are relevant to the affected genotype

A pedigree can support, but not replace, molecular evaluation

Pathologic association

Altered surfactant homeostasis

Abnormal lamellar-body ultrastructure

Variable alveolar and interstitial changes

Slide 18 · ABCA3: The typical early-life phenotype

Infant in first

Months of life

Progressive

Respiratory failure

Severe disease

Course

Rapidly progressive respiratory failure with a frequently fatal outcome in this presentation.

Slide 19 · ABCA3: Disease may present beyond infancy

A minority of affected patients first come to attention in older childhood or adulthood.

The later phenotype is often a chronic interstitial lung disease.

An adult presentation does not exclude an inherited surfactant disorder.

The section provides no reliable prevalence or age-specific penetrance estimates.

Slide 20 · ABCA3 has a broad clinical spectrum

More typical clinical pattern

Presentation in the first few months

Rapidly progressive respiratory failure

Severe prognosis account

Less common clinical pattern

Recognition in older children or adults

Chronic interstitial lung disease

Severity cannot be inferred from age alone

Slide 21 · SFTPC encodes surfactant protein C

SP-C belongs to the hydrophobic surfactant protein group.

Together with surfactant lipids, it helps reduce alveolar surface tension.

SFTPC is the second most commonly mutated gene in the source section.

The disorder follows an autosomal dominant inheritance pattern.

Slide 22 · SFTPC: Dominant inheritance and variable course

Autosomal dominant

SFTPC mutation

Surfactant protein C

Pathway altered

Highly variable

Clinical course

The textbook does not provide one obligatory age of onset or disease trajectory for SFTPC-associated disease.

Slide 23 · Surfactant-protein misfolding can injure type II cells

Some inherited

Surfactant-protein defects

Abnormal protein

Folding

Unfolded-protein

Response

Type II-cell vulnerability

To injury

Related Robbins context: This mechanism is described for rare familial interstitial fibrosis.

Slide 24 · SFTPC: Interpretation requires phenotype awareness

The clinical course may be highly variable between affected individuals.

Neither severe neonatal disease nor adult interstitial disease is obligatory.

Protein C deficiency is one of the conditions with potentially informative IHC findings.

A histologic pattern alone does not establish a specific SFTPC mutation.

Slide 25 · SFTPB encodes the surface-active protein B

SP-B is a hydrophobic surfactant protein.

It cooperates with the lipid layer to reduce air–liquid surface tension.

SFTPB is the third most commonly mutated gene in this source section.

The associated disorder has autosomal recessive inheritance.

Slide 26 · SFTPB deficiency may present in a full-term infant

Full-term

Newborn

Progressive distress

Soon after birth

Severe respiratory

Failure

A severe neonatal surfactant phenotype is not confined to prematurity.

Slide 27 · SFTPB deficiency: Prognosis

The typical reported phenotype has relentless early respiratory distress.

Death between 3 and 6 months without lung transplantation.

The prognosis described applies to the typical severe deficiency phenotype.

No genotype-specific treatment-response rates are stated in this source section.

Slide 28 · Severe genetic dysfunction differs from simple immaturity

Prematurity-related RDS

Surfactant deficiency from pulmonary immaturity

Strong relationship with gestational age

Lung maturation and exogenous surfactant are central in source discussion

Inherited SFTPB deficiency

May affect a full-term newborn

Autosomal recessive protein deficiency

Severe course can persist despite the absence of prematurity

Slide 29 · Comparative clinical profiles of the three genes

Gene

Typical source-described presentation

Important exception / course

ABCA3

First months: rapidly progressive respiratory failure

Later childhood or adult ILD possible

SFTPC

Variable timing and severity

Highly variable clinical course

SFTPB

Full-term neonate: distress soon after birth

Severe course; transplant mentioned

Slide 30 · Clinical onset alone is not a molecular diagnosis

Useful clinical clues

Full-term severe neonatal respiratory distress

A family history compatible with dominant disease

Chronic ILD in an older child or adult

Limits of inference

Overlapping phenotypes across genetic groups

A variable course can occur within a gene group

Microscopy and protein findings require correlation

Slide 31 · Histology: A mixed alveolar and interstitial pattern

Intraalveolar

Granular material

Type II pneumocyte

Hyperplasia

Interstitial

Fibrosis

Alveolar

Simplification

These findings occur in variable amounts; They are not four universal obligatory criteria.

Slide 32 · Intraalveolar material is pink and granular

Granular airspace deposits

The intraalveolar material is eosinophilic on routine histology.

Amounts vary between cases.

Airspace material alone does not distinguish genetic disease from PAP.

Schematic — not an H&E image

Slide 33 · Type II pneumocyte hyperplasia reflects epithelial response

Type II epithelial compartment

Type II pneumocyte hyperplasia is a listed morphologic feature.

Type II cells normally synthesize surfactant and repair injured alveolar lining.

Thus the affected cell population is also an epithelial repair population.

Schematic — not a histologic specimen

Slide 34 · Interstitial fibrosis adds a restrictive lung component

Normal thin septa

Thickened fibrotic septa

Native schematic: Septal thickness is illustrative, not measured.

Slide 35 · Alveolar simplification indicates architectural change

Alveolar simplification is part of the morphologic spectrum.

It should be interpreted with the accompanying epithelial and interstitial findings.

The short textbook section does not assign simplification to one gene alone.

Architectural abnormality is not equivalent to a genotype-specific histologic diagnosis.

Slide 36 · Histologic findings are variable, not pathognomonic

Finding

Meaning for interpretation

Pink granular intraalveolar material

Supports an airspace component; not specific

Type II pneumocyte hyperplasia

Shows involvement of the surfactant-producing epithelium

Interstitial fibrosis

Explains a chronic interstitial phenotype

Alveolar simplification

Signals altered alveolar architecture

Slide 37 · Protein immunohistochemistry: Intended target matters

Surfactant protein B deficiency

IHC may demonstrate lack of SP-B.

A negative stain must be interpreted for the relevant deficiency.

Surfactant protein C deficiency

IHC may demonstrate lack of SP-C.

An abnormal stain is not a complete stand-alone molecular characterization.

Slide 38 · IHC findings and genetic findings answer different questions

IHC

Protein expression

Morphology

Tissue response

Ultrastructure

Organelle phenotype

Genetics

Gene-level etiology

Integrated interpretation prevents treating a single microscopic feature as a universal genotype assay.

Slide 39 · Lamellar bodies are an ultrastructural diagnostic compartment

Lamellar bodies occur within type II pneumocytes.

All three genetic groups may exhibit ultrastructural abnormalities.

The source specifically singles out a characteristic ABCA3-associated pattern.

Schematic — not electron microscopy

Slide 40 · ABCA3: Small lamellar bodies with dense cores

Conceptual normal lamellation

ABCA3-associated small, dense-core pattern

Schematic only — the original textbook electron micrograph is not reproduced.

Slide 41 · Electron microscopy provides a high-value clue

Small lamellar bodies containing electron-dense cores are characteristic of ABCA3-associated disease.

This organelle pattern directly links an epithelial transporter to ultrastructure.

The textbook regards this pattern as diagnostic for ABCA3 mutation.

No electron micrograph has been reproduced in this lecture.

Slide 42 · The ultrastructural phenotype differs from PAP

Genetic surfactant dysfunction

Lamellar-body abnormalities within type II cells

ABCA3 has a characteristic dense-core pattern

May also show alveolar and interstitial injury

Pulmonary alveolar proteinosis

Lamellar bodies in type II cells are normal

Macrophage-mediated clearance is defective

Surfactant-rich material fills airspaces

Slide 43 · Pulmonary alveolar proteinosis: Clearance failure

Deficient GM-CSF

Signaling

Impaired alveolar

Macrophage function

Reduced surfactant

Catabolism

Surfactant accumulation

In airspaces

This is a macrophage-centered mechanism, not the same primary lesion as ABCA3/SFTPB/SFTPC dysfunction.

Slide 44 · PAP: Alveolar deposits with relatively preserved walls

PAP-like airspace filling

PAP has abundant surfactant-containing intraalveolar precipitates.

Minimal inflammation and normal alveolar walls in its illustrated case.

Type II-cell lamellar bodies are ultrastructurally normal.

Schematic — not a PAP histology micrograph

Slide 45 · PAP and inherited surfactant dysfunction: Practical contrast

Feature

PAP

Genetic dysfunction

Primary process

Impaired clearance

Altered trafficking / secretion

Key compartment

Alveolar macrophage

Type II pneumocyte

Lamellar bodies

Typically normal

May be abnormal

Microscopic emphasis

Airspace deposits

Deposits + epithelial/interstitial changes

Slide 46 · An inherited condition is not the same as every congenital PAP

Hereditary PAP

Defect in GM-CSF or GM-CSF receptor genes

Very rare neonatal presentation

Problem is impaired macrophage signaling

Genetic surfactant dysfunction

ABCA3, SFTPC or SFTPB pathway

Transport or protein biology is affected

Abnormal type II-cell lamellar bodies possible

Slide 47 · Premature-infant RDS: The mechanism is developmental

Pulmonary

Immaturity

Reduced surfactant

Availability

Recurrent alveolar

Collapse

Respiratory

Distress

This pathway is distinct from an inherited surfactant protein or transporter defect.

Slide 48 · RDS and genetic disease share a downstream consequence

Shared consequences

Reduced effective surface tension control

Poor alveolar stability

Respiratory distress and impaired gas exchange

Different starting lesions

Immaturity of surfactant synthesis in typical neonatal RDS

Mutations in surfactant pathway proteins in inherited disease

Different prognostic patterns and context

Slide 49 · Diagnostic synthesis starts with the clinical pattern

Age and severity

Of onset

Prematurity and

Perinatal context

Airspace/interstitial

Pathology

Protein, EM and

Genetic correlation

Teaching synthesis — not a validated clinical testing algorithm.

Slide 50 · Gene-oriented interpretation of clinical clues

Observation

Genetic association suggested by Robbins

Severe disease in first few months

Common ABCA3 presentation

Full-term infant with rapid postnatal decline

Typical severe SFTPB-deficient pattern

Dominant-family pattern with variable course

SFTPC-compatible clinical context

Chronic ILD in older child or adult

Can occur with ABCA3; not gene-specific

Slide 51 · Pathology-oriented interpretation of morphologic clues

Observation

Interpretation / limitation

Pink granular alveolar material

Nonspecific; consider PAP among the differential

Type II hyperplasia and fibrosis

Compatible with surfactant-associated epithelial injury

Lack of SP-B or SP-C on IHC

Supports the corresponding protein deficiency in context

Small lamellar bodies with dense cores

Characteristic ABCA3-associated EM finding

Slide 52 · Case 1: Severe disease in a full-term newborn

A full-term infant develops progressive respiratory distress shortly after birth.

Which inherited surfactant disorder has this typical presentation?

What inheritance pattern would be expected?

What could surfactant-protein immunostaining show?

Slide 53 · Case 1: Interpret the pattern

Full-term

Newborn

Progressive distress

Soon after birth

SFTPB deficiency

Is a strong clue

Autosomal recessive inheritance; Absent SP-B may be detected by IHC in the deficiency phenotype.

Slide 54 · Case 2: An infant with abnormal lamellar bodies

An infant develops respiratory failure. Electron microscopy reveals small lamellar bodies containing dense cores.

Which gene is specifically associated with this ultrastructural appearance?

Which normal protein function does that gene support?

Slide 55 · Case 2: Use ultrastructure mechanistically

Small lamellar

Bodies

Electron-dense

Cores

ABCA3-associated

Dysfunction

Altered lipid

Transport

The source designates the dense-core lamellar-body pattern as diagnostic for ABCA3 mutation.

Slide 56 · Case 3: Variable familial interstitial disease

Several relatives develop interstitial lung disease of differing severity; The pedigree is compatible with dominant inheritance.

Which surfactant protein gene belongs in the differential?

Why must the disease severity remain an open question?

Slide 57 · Case 3: Inheritance is useful but not definitive

Autosomal dominant

Family pattern

Variable clinical

Severity

SFTPC-associated

Disease is compatible

A compatible pedigree does not replace molecular confirmation or exclude other inherited ILD causes.

Slide 58 · Integrated gene–phenotype–morphology map

Disease gene

Presentation emphasized

Pathology clue

ABCA3

Infant respiratory failure; occasional later ILD

Small dense-core lamellar bodies

SFTPC

Autosomal dominant; highly variable

Loss of SP-C may be seen on IHC

SFTPB

Full-term neonate; rapidly progressive

Loss of SP-B may be seen on IHC

Slide 59 · Five conclusions to retain

Genetic surfactant disorders are type II-cell-centered diseases with diverse presentations.

ABCA3 is the leading gene; The distinctive EM clue is a dense-core lamellar body.

SFTPC disease is autosomal dominant and clinically heterogeneous.

Severe SFTPB deficiency classically affects full-term neonates.

Differentiate impaired production/handling from PAP-related failure of clearance.

Slide 60 · Reference and scope of this lecture

Primary source: Robbins, Cotran & Kumar, Pathologic Basis of Disease, 11th ed. (2026), “Surfactant Dysfunction Disorders.”

Related pathology context: alveolar anatomy, pulmonary alveolar proteinosis and genetic interstitial fibrosis.

Physiologic context: surfactant maturation and neonatal respiratory distress syndrome.

Schematic figures are original, editable teaching graphics; they are not observed specimens.