Pulmonology & Hepatology & Medical Genetics
Alpha-1 antitrypsin deficiency
Alpha-1 antitrypsin deficiency (AATD) is the most common serious inherited genetic disorder in adults of European origin. Its estimated prevalence is 1 in 2,000 to 5,000 births in Northern European and Canadian populations, representing approximately 100,000 people in Canada carrying the severe Pi*ZZ genotype. Alpha-1 antitrypsin (AAT) is a 52 kDa glycoprotein synthesized mainly by hepatocytes. It is the primary inhibitor of circulating serine proteases, particularly neutrophil elastase (NE), protecting lung parenchyma from enzymatic destruction during each inflammatory or infectious episode. The coding gene is SERPINA1 (chromosome 14q32.1), with over 120 allelic variants identified and classified by the Pi system.Protease inhibitor). The normal M allele produces a functional protein in normal quantities. The pathological Z allele (Glu342Lys mutation) in the homozygous state (Pi*ZZ) reduces serum AAT levels to 10–15 % of normal and causes intracellular polymerization of mutated AAT within hepatocytes into insoluble polymers—simultaneously creating a deficiency in lung protection (quantitative AAT deficiency in the alveoli) and a toxic hepatocellular accumulation of polymerized AAT (hepatotoxic gain of function). The disease therefore presents a dual picture: obstructive lung disease with panlobular emphysema predominantly in the basal regions, and chronic liver disease that can progress to cirrhosis and hepatocellular carcinoma. The disease remains largely underdiagnosed—85 to 95 % of Pi*ZZ patients are estimated to be undiagnosed in Canada, with an average diagnostic delay of 5 to 8 years.
Genotypes and serum AAT levels
| Pi genotype | Serum AAT level | Clinical significance |
|---|---|---|
| MM | 1.0–2.0 g/L (100 %) | Normal — no risk related to AATD; allele frequency M ≈ 95 % in the Canadian population |
| MS | 0.80–1.0 g/L (80 %) | Heterozygous carrier S - slightly reduced rate; no significant clinical risk alone; may potentiate other factors (tobacco, alcohol) |
| MZ | 0.50–0.70 g/L (50–60 %) | Heterozygous carrier Z — moderately increased pulmonary risk in smokers; modest hepatic risk (neonatal hepatitis, cirrhosis <5 % of cases); frequency in Canada: approximately 1 in 30–50 |
| SZ | 0.30–0.45 g/L (35–45 %) | Compound heterozygote - intermediate lung risk in smokers; lower hepatic risk than Pi*ZZ (S allele polymerizes poorly with Z) |
| ZZ | 0.10–0.20 g/L (10–15 %) | Severe genotype — panlobular emphysema (bases) in >80 % of smokers and 25–40 % of non-smokers; hepatopathy in 35–40 % of cases, cirrhosis 10–15 % in adulthood, HCC risk ×5–20; represents 95 % of diagnosed severe DAATs |
| Null/Null | ≈ 0 g/L (undetectable) | Rare mutations (nonsense, deletions) — very severe emphysema even in non-smokers; no liver risk (no accumulation as no protein produced) |
Pathophysiology — double mechanism of injury
- Pulmonary mechanism — protease/antiprotease imbalance: Deficient AAT → neutrophil elastase not inhibited during infections or exposure to inhaled particles → progressive destruction of alveolar elastin and collagen → panlobular emphysema predominantly basal (destruction of the entire acinus, without centrolobular predominance—unlike smoker's centrolobular emphysema with apical predominance) → hyperinflation, air trapping, irreversible obstruction; smoking multiplies the risk of emphysema by 5–10 in Pi*ZZ and accelerates FEV1 decline (150 mL/year for smoker Pi*ZZ vs 50 mL/year for non-smoker Pi*ZZ) — advances symptom onset by 20 years
- Hepatic mechanism — intrahepatocyte polymerization (loop-sheet polymerization): the Z mutation alters AAT conformation → spontaneous polymerization → insoluble polymers trapped in the rough endoplasmic reticulum → PAS-positive diastase-resistant inclusions (PAS-D - pink intracytoplasmic globules in periportal hepatocytes - pathognomonic) → endoplasmic reticulum stress → UPR (unfolded protein response) → hepatocyte apoptosis → fibrosis → cirrhosis; this mechanism is independent of serum deficiency and explains why augmentation therapy has no effect on liver damage
- Other systemic involvements: necrotizing panniculitis (ulcerated skin lesions on the lower limbs — rare but characteristic); membranoproliferative glomerulonephritis (deposits of polymerized AAT); intracranial and aortic aneurysms (destruction of parietal elastin by non-neutralized elastase)
Diagnosis
- Screening indications - situations requiring serum AAT level testing: COPD or emphysema in a young patient (<45 years old), especially with panlobular emphysema on CT scan; COPD without smoking or with light smoking history (<20 pack-years); unexplained chronic liver disease (child or adult), cryptogenic cirrhosis, neonatal cholestatic hepatitis; recurrent necrotizing panniculitis; family history of AATD, early-onset COPD, or cryptogenic cirrhosis; sibling or child of a known Pi*ZZ individual (mandatory family screening)
- Serum AAT level: immunoturbidimetric or immunonephëlometric method — normal 1.0–2.0 g/L; value <1.0 g/L → genotyping; pitfall: AAT is a positive acute phase protein — acute inflammation (infection, surgery) can mask a deficiency by falsely normalizing the level; always interpret with CRP — repeat the test at a distance from the inflammatory episode if CRP is high
- Pi genotyping: phenotyping by isoelectric focusing (IEF) or molecular genotyping by allele-specific PCR (Z and S alleles) or SERPINA1 sequencing (rare Null variants); recommended as first-line in modern laboratories — faster and more accurate than IEF
- Pulmonary assessment: spirometry (FEV1, FVC, ratio — obstructive syndrome); reversibility test; high-resolution chest CT scan (basal panlobular emphysema — hypodense areas, alveolar destruction); plethysmography (increased TLC, air trapping); DLCO (decreased if extensive emphysema)
- Liver function tests: AST, ALT, GGT, ALP, bilirubin, albumin, PT; liver elastography (FibroScan) or FIB-4/APRI for non-invasive fibrosis; EGD if cirrhosis (varices); semi-annual HCC screening by ultrasound + AFP if cirrhosis; liver biopsy if diagnostic doubt — pathognomonic periportal PAS-D positive globules
Treatment
| Intervention | Details and level of evidence |
|---|---|
| Quitting smoking — absolute priority | Most impactful single intervention—reduces FEV1 decline from 150 mL/year to 50 mL/year in Pi*ZZ; delays symptoms by 10–20 years; smoking absolutely contraindicated in Pi*ZZ or SZ; varenicline, bupropion, nicotine replacement therapy recommended; also avoid smoked cannabis and occupational exposures (dusts, fumes, isocyanates) |
| Augmentation Therapy (ATh) | IV infusion of purified AAT from pooled human plasma (Prolastin-C or Zemaira — 60 mg/kg/week or 120 mg/kg every 2 weeks) — only specific treatment approved by Health Canada; objective: maintain serum AAT level >0.5 g/L (Gadek's protective threshold); indicated in Pi*ZZ (or SZ) with documented lung involvement (FEV1 25–80 %of predicted), non-smoker or former smoker abstinent ≥6 months; level of evidence: RAPID study (Dirksen 2010, Thorax) — slowdown of lung densitometry decline by 34 %; RAPID extension study — benefit on long-term FEV1 decline; does not act on liver damage (intrahepatic accumulation mechanism); cost $50,000–$100,000 $/year — exceptional RAMQ program; adverse effects: headaches, fever, chills (5–10 % ) |
| COPD Treatment Management | LABA/LAMA (indacaterol, salmeterol, tiotropium, umeclidinium) per GOLD; ICS if ≥2 exacerbations/year with caution (pneumonia); respiratory rehabilitation; long-term O2 if PaO2 <55 mmHg; annual influenza + PCV13 + PPSV23 vaccinations |
| Lung transplantation | If FEV1 <25 % of predicted despite optimal treatment or high BODE; 5-year survival 50–60 % — comparable to other COPD etiologies; only option in terminal pulmonary forms |
| Hepatic support | Absolute alcohol abstinence; hepatitis A and B vaccination; treatment of cirrhosis complications (varices, ascites, encephalopathy); semiannual HCC surveillance (ultrasound + AFP); liver transplantation if decompensated cirrhosis or HCC — definitively corrects liver disease (donor liver produces normal AAT) but does not improve pre-existing lung involvement |
| Emerging therapies | Fazirsiran (ARNi ciblant SERPINA1 — SEQUOIA trial phase 3 2023 — réduction >80 % des polymères hépatiques + amélioration de la fibrose hépatique) ; thérapie génique AAV-SERPINA1 (phase 1/2 — restauration des taux sériques) ; chaperones pharmacologiques (correction du repliement Z) ; AAT recombinante inhalée (phase 2) |
ℹ️
Alpha-1 antitrypsin deficiency is underdiagnosed to an alarming extent — 85 to 95 % of Pi*ZZ patients would not be diagnosed, with an average delay of 5 to 8 years. Any physician evaluating a patient with COPD or early emphysema without sufficient smoking history, or with basal predominant panlobular emphysema on CT scan, should measure serum AAT. A single blood test is sufficient to initiate the workup — and an early diagnosis can radically change the prognosis through smoking cessation and access to augmentation therapy.
Severe acute exacerbation of COPD on NIV — respiratory emergency
Dial 911 Go immediately to the emergency room in case of rapidly progressive shortness of breath, cyanosis, confusion or agitation, retractions, or SpO2 <90 % in a patient with alpha-1 antitrypsin deficiency and advanced COPD. Infectious exacerbations are particularly dangerous in AATD - the influx of neutrophils into lungs insufficiently protected by AAT accelerates irreversible alveolar destruction with each episode. Annual influenza and pneumococcal vaccination is a priority.
Consult at Clinique Omicron
Clinique Omicron physicians prescribe serum alpha-1 antitrypsin levels in patients with early or unexplained COPD, panlobular emphysema, or a family history of AATD, interpret the results, and refer to medical genetics, pneumology, or hepatology for diagnostic confirmation and access to augmentation therapy. Consultations are available at our service points in Quebec as well as through telemedicine. To book an appointment, visit cliniqueomicron.ca.
The content of this page is for informational purposes only and does not replace the advice of a qualified healthcare professional. Alpha-1 antitrypsin deficiency is a serious chronic condition requiring multidisciplinary follow-up by a pulmonologist and a hepatologist.
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