a 1 Antitrypsin Deficiency

Slide 1 · α1-Antitrypsin deficiency

Molecular pathogenesis • hepatic morphology • pulmonary disease

Dr Abu Suraih Sakhri

MBBS, MD (Pathology)

www.abusuraihsakhri.com

Slide 2 · Learning outcomes

Explain how the same variant causes distinct liver and lung injury.

Interpret Pi nomenclature and genotype–phenotype relationships.

Recognize the characteristic PAS–diastase-resistant hepatocellular globules.

Connect panacinar emphysema to antiprotease loss and clinical progression.

Slide 3 · One gene, two organ mechanisms

SERPINA1 / α1AT variant

Defective secretion + ER retention

Liver: Toxic protein accumulation

Lung: Antiprotease deficiency

The hepatic and pulmonary lesions arise by different mechanisms.

Slide 4 · Core definition

Inherited disorder of α1-antitrypsin protein folding and secretion.

Circulating antiprotease levels are markedly reduced in severe deficiency.

Hepatic retention of mutant protein and pulmonary antiprotease failure coexist.

Slide 5 · Where α1-antitrypsin is made

Hepatocyte synthesis

ER folding and quality control

Golgi trafficking

Release into blood

Normal α1AT reaches tissues after hepatocyte production.

Slide 6 · Protein identity

α1-antitrypsin (α1AT or AAT) is a plasma glycoprotein.

The mature protein contains 394 amino acids.

It is a member of the serine protease inhibitor (serpin) family.

Slide 7 · Main physiologic targets

Neutrophil elastase

Cathepsin G

Proteinase 3

These proteases are released by neutrophils at inflammatory sites.

Slide 8 · The normal pulmonary balance

Neutrophil recruitment

Local release of proteases

α1AT restrains proteolysis

Alveolar matrix protected

Protection depends on an effective protease–antiprotease balance.

Slide 9 · Why genetic nomenclature uses “Pi”

“Pi” abbreviates protease inhibitor.

Protein variants were originally distinguished by electrophoretic migration.

Two letters designate the pair of inherited alleles.

Slide 10 · Major genotypes at a glance

PiMM: Usual protein

PiMZ: Intermediate level

PiZZ: Severe deficiency

Serum expression shows codominance; Severe clinical disease is usually associated with two deficient alleles.

Slide 11 · PiMM: Reference genotype

PiMM is the most common genotype in the Robbins description.

It is the usual (wild-type) reference for protein level.

PiMM in approximately 90% of individuals.

Slide 12 · PiMZ: Intermediate plasma concentration

The M and Z alleles are both expressed.

A PiMZ carrier produces an intermediate plasma concentration of α1AT.

Intermediate level does not imply that every carrier develops clinically apparent disease.

Slide 13 · PiZZ: High-risk genotype

PiZZ homozygotes have very low circulating α1AT.

Levels at approximately 10% of normal.

Severe antiprotease deficiency predisposes to emphysema; Intracellular Z protein predisposes to hepatic injury.

Slide 14 · Genotype, protein level, and mechanism

Genotype

Circulating α1AT

Hepatic Z protein

PiMM

Reference/normal

Absent

PiMZ

Intermediate

One Z allele may contribute retention

PiZZ

~10% of usual level

Marked ER retention

Slide 15 · Population context and limits

PiZZ in approximately 1 of 1,800 live births among people of Northern European descent.

That estimate must not be generalized to all populations.

Genotype prevalence is not equivalent to the prevalence of clinical cirrhosis or emphysema.

Slide 16 · Loss of function versus toxic gain of function

Lung injury

Too little active circulating α1AT

Excess neutrophil protease activity

Alveolar septal destruction

Liver injury

Mutant Z protein retained in hepatocytes

ER stress and unfolded protein response

Cell injury and potential apoptosis

Slide 17 · Normal intracellular trafficking

Nascent α1AT chain

Folding in endoplasmic reticulum

Transport to Golgi

Secreted mature α1AT

A secretion-competent fold permits exit from the ER.

Slide 18 · Z protein: Blocked export

SERPINA1 Z protein

Abnormal conformation

Polymerization / aggregation

ER retention

A defect in folding and ER-to-Golgi transport lowers secretion.

Slide 19 · Z allele: Correct molecular designation

The canonical Z substitution is Glu342Lys (E342K), using mature-protein numbering.

The variant favors misfolding and polymer formation.

Robbins’ converted text says “glutamine”; Authoritative molecular references specify glutamic acid.

Slide 20 · Protein retention is a hepatocyte insult

Misfolded α1AT-Z

Intracellular aggregation

ER stress

Hepatocyte injury

This injury requires the retained mutant product, not simply absence from blood.

Slide 21 · Unfolded protein response

Misfolded ER cargo

ER stress sensing

Unfolded protein response

Potential apoptosis

The response is initially adaptive but prolonged stress can damage cells.

Slide 22 · Why the liver mechanism is “toxic gain of function”

The mutant molecule acquires an injurious propensity to accumulate.

Intracellular aggregates activate stress responses in producing hepatocytes.

The liver phenotype is not explained by loss of extracellular elastase inhibition.

Slide 23 · Incomplete hepatic penetrance

PiZZ hepatocytes characteristically retain α1AT-Z.

Only a subset of PiZZ individuals develops overt hepatic disease.

Additional genetic and environmental modifiers, not yet specified in that section.

Slide 24 · Shared genotype, divergent organ outcomes

Severe lung phenotype

Low antiprotease activity

Protease-driven extracellular injury

Smoking markedly accelerates disease

Severe hepatic phenotype

Retention of misfolded protein

Intracellular stress and tissue remodeling

Variable penetrance despite globule accumulation

Slide 25 · Hepatic disease across the lifespan

Presentations range from infancy to adult life.

Severe infantile cases can progress rapidly toward cirrhosis.

Other individuals present as adults with chronic hepatitis, cirrhosis, or hepatocellular carcinoma.

Slide 26 · Characteristic hepatocellular inclusions

Original conceptual schematic — not a tissue image

Round-to-oval cytoplasmic globules

Most conspicuous on PAS after diastase

Reflect accumulated mutant α1AT

Slide 27 · Why PAS–diastase highlights globules

The retained glycoprotein is PAS-positive.

Diastase removes PAS-reactive glycogen; Characteristic α1AT inclusions persist.

The expected histologic signal is magenta cytoplasmic globules.

Slide 28 · Periportal predominance in early disease

Original conceptual schematic — not a tissue image

Periportal region

Toward central region

Globules initially appear in periportal hepatocytes.

More advanced disease may involve central hepatocytes.

Zonal location reflects pattern of retention—not a stand-alone measure of injury.

Slide 29 · Globule count is not a severity score

The proportion of globule-bearing hepatocytes correlates poorly with disease severity.

The diagnostic inclusion and the magnitude of ongoing injury are different variables.

A small biopsy cannot reliably stage disease by inclusions alone.

Slide 30 · Important neonatal morphology pitfall

Neonatal hepatitis can precede the development of visible cytoplasmic globules.

In PiZZ disease, characteristic globules generally emerge at approximately 12 weeks or later.

Absence of inclusions in early infancy cannot exclude α1AT deficiency.

Slide 31 · What the pathologist should actually identify

Original conceptual schematic — not a tissue image

Hepatocellular rather than extracellular globules

Cytoplasmic, round/ovoid inclusions

Persistent PAS positivity after diastase

Slide 32 · Biopsy findings: Characteristic versus insufficient

Supportive of α1AT deficiency

Numerous PAS-D-resistant hepatocyte globules

Appropriate periportal distribution

Compatible liver injury pattern

Insufficient as sole evidence

One isolated nonspecific globule

Cirrhosis without genotype/biochemical context

Negative globules in very young infant

Slide 33 · Neonatal clinical presentation

Severe early-onset disease may be recognized as neonatal hepatitis.

Some severe presentations progress relatively rapidly to cirrhosis.

The absence of mature PAS-D inclusions early in life is a critical biopsy limitation.

Slide 34 · How chronic hepatic injury evolves

Protein retention

Persistent hepatocellular injury

Repair and fibrous remodeling

Cirrhosis in affected patients

Cirrhosis develops in a susceptible subset rather than every PiZZ individual.

Slide 35 · Adult hepatic manifestations

Chronic hepatitis may be the presenting pattern.

Cirrhosis can follow longstanding hepatic injury.

Hepatocellular carcinoma is a recognized complication, with or without established cirrhosis.

Slide 36 · Hepatocellular carcinoma risk

Hepatocellular carcinoma in 2%–3% of adults with PiZZ.

The tumor usually, but not invariably, occurs in a cirrhotic liver.

This figure is source-specific; It is not an individualized or lifetime prediction.

Slide 37 · Hepatic phenotypic spectrum

No overt disease

Infantile hepatitis

Chronic injury / cirrhosis

Hepatocellular carcinoma

Clinical trajectories differ despite the same PiZZ genotype.

Slide 38 · Why low α1AT injures the lung

Reduced functional α1AT

Poor elastase inhibition

Alveolar elastin digestion

Panacinar emphysema

Pulmonary disease is predominantly a loss-of-function phenotype.

Slide 39 · Neutrophils as a protease source

Inflammation recruits neutrophils into lung tissue.

Activated cells release elastase and related proteases.

Insufficient inhibitor activity permits ongoing extracellular proteolysis.

Slide 40 · Protease–antiprotease balance

Protected alveolus

Physiologic inflammatory protease release

α1AT limits elastolytic injury

Alveolar septa and recoil preserved

Deficient alveolus

Same proteases act with less restraint

Elastin and alveolar walls are damaged

Recoil and gas-exchange surface are lost

Slide 41 · Normal acinus and panacinar enlargement

Normal acinus

Panacinar enlargement

Native schematic — not a histologic specimen.

Slide 42 · The panacinar emphysema pattern

The acinus is diffusely enlarged, from respiratory bronchiole through distal alveoli.

α1AT deficiency is a classic cause of this morphologic pattern.

Alveolar wall destruction decreases elastic recoil and available capillary bed.

Slide 43 · Panacinar versus centriacinar emphysema

Panacinar

Uniform involvement of acinus

Often lower zones and lung bases

Strong association with α1AT deficiency

Centriacinar

Central/proximal acinar involvement first

Classically upper-lobe predominant

Strong association with smoking

Slide 44 · Lung distribution is a pattern, not a genetic test

α1AT-related panacinar disease is often most severe basally.

Basal predominance differs from the usual apical tendency of smoking-related centriacinar disease.

Morphology raises suspicion but is not sufficient to establish genotype.

Slide 45 · Smoking magnifies proteolytic damage

Smoke / inhaled toxicants

Inflammation and neutrophil influx

More local protease release

Accelerated parenchymal destruction

Earlier and more severe emphysema in PiZZ individuals who smoke.

Slide 46 · Why loss of recoil obstructs airflow

Alveolar septal loss

Less radial traction on small airways

Expiratory bronchiolar collapse

Airflow limitation

Obstruction can be functional, without a lumen-filling lesion.

Slide 47 · Consequences of alveolar destruction

Enlarged distal airspaces provide less efficient gas-exchange surface.

Loss of elastic tissue impairs expiratory driving pressure.

Capillary bed reduction and small-airway collapse contribute to clinical dysfunction.

Slide 48 · Lung microscopic morphology: Principles

Original conceptual schematic — not a tissue image

Enlarged airspaces with reduced septal support

Abnormally enlarged alveolar airspaces

Thinning and loss of alveolar septa

Reduced attachments to small airways

Slide 49 · Clinical–pathologic interpretation of emphysema

Panacinar morphology in a young or minimally exposed patient warrants suspicion for severe α1AT deficiency.

Smoking history remains an important modifier of risk and presentation.

Lung morphology and serum genotype address complementary questions.

Slide 50 · Diagnostic pathway: Establish the defect

Compatible lung or liver phenotype

Quantitative serum α1AT

PI protein typing / SERPINA1 testing

Interpret with clinical context

Supplemental clinical diagnostic framework from GeneReviews.

Slide 51 · What serum α1AT measurement tells us

A low concentration supports a quantitative antiprotease defect.

It does not by itself resolve every genotype or functional variant.

Molecular and/or protein phenotyping helps define the cause.

Slide 52 · Why genotype or phenotype confirmation matters

Protein electrophoretic phenotypes and SERPINA1 alleles are related but distinct test outputs.

PiZZ, PiMZ and other allelic combinations may have different risk profiles.

Targeted testing may not detect every rare or null allele.

Slide 53 · Biopsy and genotype answer different questions

Biopsy

Shows hepatocellular storage and tissue damage

Reveals PAS-D globules where present

May show hepatitis/fibrotic remodeling

Protein / genetic testing

Demonstrates deficient protein concentration

Defines electrophoretic phenotype

Identifies pathogenic SERPINA1 variants

Slide 54 · Implications for relatives

The inherited alleles may be present in family members without clinically evident disease.

Risk assessment is improved by genotype-aware family evaluation.

A normal clinical examination is not proof of a usual genotype.

Slide 55 · Therapeutic target follows the pathogenesis

Pulmonary component

Protect against further exposure-driven injury

Address obstructive lung consequences

α1AT augmentation is a pulmonary option in selected patients

Hepatic component

Monitor for clinically important liver injury

Advanced liver failure may require transplantation

Augmentation does not remove hepatic mutant deposits

Slide 56 · Liver transplantation: Precise interpretation

Replacing the diseased liver addresses the hepatic source of retained Z protein.

With an AAT-replete donor liver, serum α1AT is restored.

Pre-existing emphysematous architecture is not reversed by transplantation.

Slide 57 · Reconciling the transplantation statements

Robbins says liver transplantation is curative for hepatic disease but does not alter pulmonary disease.

Current transplant literature distinguishes restored inhibitor production from persistent established lung destruction.

Avoid promising that restoration of serum α1AT repairs existing emphysema.

Slide 58 · Case 1 · neonatal liver disease

An infant with hepatitis undergoes liver biopsy before 12 weeks of age.

No characteristic PAS-D-resistant globules are identified.

Question: Does negative globule staining exclude PiZZ-associated disease?

Discussion prompt · interpret the mechanism and limitations

Slide 59 · Case 1 · interpretation

No: Clinically important disease can precede visible inclusion formation.

The biopsy result must be interpreted in the age-specific morphologic context.

Protein concentration and phenotype/genotype evaluation can test the hypothesis.

Slide 60 · Case 2 · emphysema pattern

An adult develops airflow obstruction with diffuse panacinar emphysema, predominantly at the lung bases.

There is a history of cigarette exposure.

Question: Which inherited defect should enter the differential?

Discussion prompt · interpret the mechanism and limitations

Slide 61 · Case 2 · interpretation

Consider severe α1AT deficiency as an explanation of the panacinar pattern.

Smoking is a potent amplifier rather than a reason to disregard genetic risk.

A protein level and PI/SERPINA1 assessment can establish the molecular basis.

Slide 62 · Case 3 · PAS–diastase finding

A biopsy contains periportal hepatocytes with round magenta cytoplasmic globules persisting after diastase digestion.

Question: Which intracellular process explains the finding?

Discussion prompt · interpret the mechanism and limitations

Slide 63 · Case 3 · interpretation

Misfolded mutant α1AT is retained and aggregates in hepatocyte ER.

The inclusions indicate abnormal protein handling rather than glycogen accumulation.

Storage is diagnostically useful but does not independently quantify disease severity.

Slide 64 · Distinguishing inherited liver diseases

Disease

Principal defect

Hallmark mechanism

α1AT deficiency

SERPINA1-related misfolding

ER-retained protein

Wilson disease

ATP7B transport dysfunction

Hepatic copper accumulation

Hemochromatosis

Iron-regulatory defect (often HFE)

Excess iron uptake / deposition

Slide 65 · Unified disease model

Z protein synthesis

ER retention → hepatic damage

Low blood α1AT → lung injury

Variable long-term clinical expression

Liver and lung effects must be evaluated separately.

Slide 66 · Key morphologic discriminators

Hepatic: PAS-positive, diastase-resistant cytoplasmic globules in hepatocytes.

Pulmonary: Panacinar emphysema, often with basal predominance.

Neither inclusion count nor lung topography alone predicts individual genotype or outcome.

Slide 67 · Four high-yield conclusions

One SERPINA1 variant can cause loss of antiprotease function and toxic intracellular protein retention.

PiZZ usually produces marked deficiency, but overt hepatic disease has incomplete penetrance.

PAS–diastase-positive hepatocellular inclusions are characteristic, yet may be absent early in infants.

Pulmonary destruction and established hepatic injury require distinct clinical assessment.

Slide 68 · References and source distinctions

Primary: Robbins, Cotran & Kumar. Pathologic Basis of Disease. 11th ed. (2026), Chapter 18, pp. 774–775; pulmonary context Chapter 15, pp. 618–620.

Supplemental molecular correction: MedlinePlus Genetics, SERPINA1; GeneReviews® Alpha-1 Antitrypsin Deficiency (updated 2023).

Supplemental clinical/transplant interpretation: Zamora et al., Ther Adv Chronic Dis (2021), PMCID: PMC8367211.

All organ and cell illustrations in this deck are original editable schematics—not histologic or radiologic specimens.