alpha-1 antitrypsin deficiency
Summary
Alpha-1 antitrypsin (A1AT) deficiency is an autosomal codominant genetic disorder caused by mutations in the SERPINA1 gene, leading to reduced or dysfunctional A1AT protein. This results in unopposed neutrophil elastase activity causing panacinar emphysema (typically lower lobe predominant) and misfolded protein accumulation in hepatocytes causing liver disease (cirrhosis, hepatocellular carcinoma). Classic presentation is early-onset emphysema in a young, non-smoking patient with liver disease.
Detail
A1AT is a protease inhibitor (serpin) produced primarily in the liver that inhibits neutrophil elastase, protecting lung tissue from proteolytic damage. The most common severe mutation is the PiZZ genotype (vs normal PiMM), which causes A1AT to misfold and polymerize within the endoplasmic reticulum of hepatocytes, leading to reduced serum A1AT levels (accumulation causes hepatocyte injury via toxic gain-of-function, while deficiency in circulation causes loss-of-function in lungs).
Pathophysiology: In the lungs, decreased A1AT allows neutrophil elastase to degrade elastin unchecked, causing panacinar (panlobular) emphysema, characteristically affecting the lower lobes (contrasted with centriacinar emphysema in smoking, which favors upper lobes). Smoking dramatically accelerates disease progression and lowers age of onset by inactivating residual A1AT and increasing neutrophil elastase burden.
In the liver, misfolded A1AT protein aggregates form PAS-positive, diastase-resistant globules in hepatocytes, visible on liver biopsy. This can cause neonatal hepatitis/cholestasis, cirrhosis, and increased risk of hepatocellular carcinoma.
Clinical clues for boards: young patient (<45) with emphysema who does not smoke or has minimal smoking history, especially with concurrent liver disease or family history of unexplained cirrhosis. Diagnosis involves low serum A1AT levels, confirmed with phenotyping/genotyping (protease inhibitor typing) showing PiZZ or other deficient alleles.
Management includes smoking cessation, bronchodilators for pulmonary symptoms, IV augmentation therapy with pooled human A1AT for severe pulmonary disease, and liver transplantation for end-stage liver disease (curative for genetic defect since transplanted liver produces normal A1AT).
Key associations for boards: panacinar emphysema (lower lobe), neonatal jaundice/cirrhosis, PAS+ globules in hepatocytes on liver biopsy, codominant inheritance pattern, chromosome 14 (SERPINA1 gene).
Sources
- First Aid for the USMLE Step 1
- Robbins and Cotran Pathologic Basis of Disease
- UpToDate: Alpha-1 antitrypsin deficiency
- Pathoma - Fundamentals of Pathology (Husain)
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