Alpha-1 Antitrypsin Deficiency & Advanced Emphysema Interventions
One misfolded protein, two injured organs, and when to operate on emphysema
Genetics and pathophysiology
The protein. Alpha-1 antitrypsin (AAT) is a serine protease inhibitor secreted mainly by hepatocytes; its main job is to neutralize neutrophil elastase in the lung. It is encoded by SERPINA1 on chromosome 14, and its alleles (the Pi system) are expressed codominantly. The Z allele (Glu342Lys) is the classic severe variant and is most common in people of Northern European ancestry.
| Genotype | Serum AAT | Clinical consequence |
|---|---|---|
| MM | Normal | Baseline risk |
| MZ | Mildly reduced | Small excess COPD risk, mainly in smokers |
| SZ | Moderately reduced | Emphysema risk, mainly in smokers |
| ZZ | About 10–15% of normal | Early emphysema and liver disease |
| Null/null | Undetectable | Severe emphysema; liver spared |
Lung injury: loss of function. With little AAT reaching the alveoli, neutrophil elastase degrades elastin in the alveolar walls, producing panacinar (panlobular) emphysema that is worst in the lower lobes, often by the 30s or 40s. Cigarette smoke oxidizes and inactivates the AAT that remains and recruits more neutrophils, so smokers with PiZZ develop disease a decade or more earlier. By contrast, ordinary smoking-related emphysema is centriacinar and upper-lobe predominant.
Liver injury: gain of function. Misfolded Z protein polymerizes and is retained in the hepatocyte endoplasmic reticulum instead of being secreted. Biopsy shows PAS-positive, diastase-resistant globules in periportal hepatocytes. The result is neonatal cholestasis, chronic hepatitis, cirrhosis, and hepatocellular carcinoma. Null alleles make no protein at all, so they cause severe lung disease without liver disease.
Recognition and testing
When to suspect AATD.
- Emphysema before age 45, or with little or no smoking history.
- Lower-lobe (basilar) panlobular emphysema.
- Unexplained liver disease or cirrhosis, including neonatal cholestasis.
- Necrotizing panniculitis: painful, ulcerating subcutaneous nodules.
- PR3-ANCA vasculitis or unexplained bronchiectasis.
- A family history of emphysema or liver disease.
Whom to test. Because the condition is badly underdiagnosed, guidelines recommend a one-time test for every adult with COPD and for adults with asthma whose obstruction is not fully reversible.
- Serum AAT levelA low level suggests deficiency. AAT is an acute-phase reactant, so inflammation, infection, pregnancy, or estrogen can lift an MZ or SZ level into the normal range; check CRP alongside.
- Phenotype or genotypeIsoelectric focusing or genotyping identifies the allele pair, such as PiZZ.
- Assess both organsSpirometry with DLCO, chest CT, liver tests, and liver imaging.
Management
Smoking cessation first. Quitting is the most effective intervention in every genotype; smoking accelerates emphysema and sharply shortens survival in PiZZ. Otherwise treat as COPD: long-acting bronchodilators, vaccinations, pulmonary rehabilitation, oxygen when indicated, and avoidance of occupational dusts and fumes.
Augmentation therapy. Weekly IV pooled human plasma AAT (60 mg/kg) raises serum levels above the protective threshold and slows the decline in CT lung density. It is reserved for severe deficiency (PiZZ, null alleles, or a level below 11 μM) with emphysema or airflow obstruction in patients who do not smoke. It also helps necrotizing panniculitis but does nothing for the liver, whose injury comes from retained protein rather than deficiency.
Check for IgA deficiency before augmentation: patients with anti-IgA antibodies risk anaphylaxis from trace IgA in plasma-derived products.
Family and liver. Each sibling of a PiZZ patient has at least a 25% chance of also being ZZ, so offer testing and genetic counseling to first-degree relatives. Protect the liver by avoiding alcohol, vaccinating against hepatitis A and B, checking liver tests periodically, and screening for HCC with ultrasound once cirrhosis develops. Liver transplantation for decompensated disease also cures the deficiency, because the new liver secretes normal AAT.
Interventions for advanced emphysema
| Intervention | Best candidate | Key points |
|---|---|---|
| Lung volume reduction surgery | Upper-lobe-predominant emphysema with low exercise capacity after rehab; nonsmoker | Survival and function benefit in NETT; prohibitive mortality if FEV1 ≤20% plus either DLCO ≤20% or homogeneous emphysema |
| Endobronchial valves | Severe hyperinflation, heterogeneous or homogeneous emphysema, complete fissures (no collateral ventilation) | One-way valves collapse the target lobe; pneumothorax in about a quarter, usually within days |
| Bullectomy | Giant bulla (≥1/3 of a hemithorax) compressing relatively healthy lung | Compressed lung re-expands, improving FEV1 and dyspnea; best when the remaining lung is relatively preserved |
| Lung transplant | Progression despite maximal therapy | Refer at BODE 5–6, FEV1 <25%, PaCO2 >50 or PaO2 <60 mm Hg; list at BODE ≥7, FEV1 <15–20%, repeated severe exacerbations, or pulmonary hypertension |
Why volume reduction works. Removing or collapsing the most hyperinflated, poorly perfused lung restores elastic recoil, lets the diaphragm regain a better length-tension relationship, and improves V/Q matching. Because AATD emphysema is basilar and often homogeneous, results of volume reduction in AATD are generally less durable than in upper-lobe smoking-related disease.
A giant bulla can mimic pneumothorax on a plain film; obtain CT before placing a chest tube, which would puncture the bulla.
BODE index. BMI, Obstruction (FEV1 % predicted), Dyspnea (mMRC scale), and Exercise capacity (6-minute walk distance) combine into a 0–10 score that predicts mortality better than FEV1 alone. COPD, including AATD, is one of the most common indications for lung transplantation.