💡 Key Clinical Pearl: Screen for Alpha-1 Antitrypsin (AAT) deficiency in any patient with COPD < age 40 or with atypical features (e.g., basal emphysema, strong family history). 🔎 AAT deficiency is autosomal recessive, prevalence ≈ 1 in 2500, and accounts for ~1% of emphysema cases. The classic severe form is the PiZZ genotype.

📖 About

AAT deficiency is a genetic disorder causing reduced inhibition of neutrophil elastase → lung & liver damage.
Main manifestations:
- 🫁 Emphysema (especially in the lung bases)
- 🍷 Cirrhosis & hepatocellular carcinoma
Normal genotype: PiMM; Severe: PiZZ.

🧬 Aetiology

AAT is a serine protease inhibitor produced in the liver, protecting lung tissue by inhibiting neutrophil elastase.
Gene location: chromosome 14q32.1.
PiZZ genotype frequency ≈ 1:2500 in Europeans.

🔎 Pathophysiology

Normal: AAT binds & inactivates neutrophil elastase → prevents alveolar wall destruction.
Deficiency: ⬇ AAT → unopposed elastase → elastin degradation → panacinar emphysema, especially in lung bases.
Genotypes:
- PiMM (normal): 100% activity
- PiSS: ~50% levels
- PiZZ: ~10% levels → severe phenotype

🧪 Genetics

AAT phenotypes defined by electrophoresis mobility (“Pi” = protease inhibitor locus).
Alleles: M (normal), S (intermediate), Z (severe reduction).
Common genotypes:
- Best: MM, MS, MZ
- Intermediate: SZ
- Worst: ZZ (classic disease)

🩺 Clinical Features

Lungs: Early-onset panacinar emphysema (bases > apices), bronchiectasis.
Liver: Cirrhosis, hepatocellular carcinoma in adults; neonatal cholestasis in infants.
Onset:
- Smokers: 30–40s
- Non-smokers: 50–60s
~10% develop significant liver disease.

🧾 Investigations

Serum AAT levels: Low (<50–80 mg/dL; <11 µmol/L).
Genotyping: Confirms alleles (e.g., PiZZ).
Liver biopsy: PAS-positive, diastase-resistant globules (AAT accumulation in hepatocytes).
Imaging: HRCT → panacinar emphysema in lower lobes.

💊 Management

Lifestyle: Absolute smoking cessation 🚭; minimise alcohol intake.
Conventional COPD care: Inhaled bronchodilators, pulmonary rehab, vaccination.
AAT augmentation therapy: IV pooled human AAT in moderate disease (not universally available in NHS).
Advanced therapies:
- Liver transplant → curative (new liver produces AAT)
- Lung transplant → for advanced emphysema
- Gene therapy → under research

⚠️ Teaching Pearls

Think of AAT deficiency in basal emphysema (vs. apical in smoking-related COPD).
Hepatic manifestations can precede lung disease, especially in children.
Never miss family screening → siblings may carry at-risk genotypes.

📚 References

3 Clinical Cases - Alpha-1 Antitrypsin (AAT) Deficiency 🧬🫁

Case 1 - Early-onset emphysema 🚬: A 34-year-old man, non-smoker, presents with progressive exertional dyspnoea and wheeze. Spirometry: FEV₁ 48% predicted, obstructive pattern. HRCT: panacinar emphysema, basilar predominance. Serum AAT: low, phenotype PiZZ. Teaching: Classic presentation is early-onset emphysema in a non-smoker. Basilar panacinar emphysema is the radiological hallmark. Smoking accelerates decline dramatically. Augmentation therapy with IV AAT is available in some centres.
Case 2 - Chronic liver disease 🍺: A 22-year-old man with no alcohol history presents with jaundice, hepatomegaly, and abnormal LFTs. Ultrasound: cirrhotic liver with portal hypertension. Biopsy: PAS-positive, diastase-resistant inclusions. Teaching: Misfolded AAT protein accumulates in hepatocytes, leading to cirrhosis and increased risk of hepatocellular carcinoma. Children may present with neonatal hepatitis; adults with cirrhosis in early/midlife. Liver transplantation cures both hepatic and pulmonary manifestations.
Case 3 - Family screening 🔍: A 38-year-old woman, sister of a man with AAT deficiency, is asymptomatic but requests testing. Spirometry normal. Serum AAT: intermediate level, phenotype PiMZ. Teaching: Heterozygotes may have near-normal lung function but are at increased risk if they smoke or develop another chronic lung insult. Family screening is important for early diagnosis, lifestyle counselling, and monitoring for complications.

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Alpha-1 Antitrypsin (AAT) deficiency