Alpha-1 antitrypsin deficiency
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A 40-year-old non-smoker presents with early-onset emphysema predominantly affecting the lower lobes. His brother has cirrhosis.
AR (codominant); SERPINA1
- Normal: MM (PiMM)
- Z allele (Glu342Lys): ZZ is severe deficiency
- S allele: SZ = moderate deficiency
- Pulmonary: Panacinar emphysema, COPD (lower lobe predominant)
- Hepatic: Neonatal hepatitis, cirrhosis, hepatocellular carcinoma
- Smoking dramatically accelerates lung disease
- Low serum AAT level (quantitative measurement) is the screening test
- Protease inhibitor (Pi) phenotyping by isoelectric focusing confirms the variant (e.g., PiZZ, PiSZ)
- SERPINA1 genotyping/sequencing when phenotype is ambiguous or to detect rare/null alleles
- Consider in early-onset (panacinar, lower-lobe) emphysema and unexplained liver disease
- AAT augmentation therapy, avoid smoking
Gene "SERPINA1": SERine Protease INhibitor. When you can't inhibit the serine proteases, they cause uncontrolled damage to the lungs (emphysema) and liver (cirrhosis)