AAT is a serine protease inhibitor that protects the lungs from proteolytic damage by neutrophil elastase.8 AAT deficiency is known to cause a variety of respiratory symptoms that generally present in the third or fourth decade of life. The AAT protein is encoded by the SERPINA1 gene and inheritance is autosomal codominant. More than 100 AAT variants, many having no clinical importance, have been identified based on their mobility using isoelectric focusing electrophoresis. The most common phenotype, designated MM, is associated with normal serum concentrations of AAT. The S (E264V) and Z (E342K) alleles represent approximately 95% of all AAT deficiency alleles and result in a reduced AAT serum concentration. Certain AAT variants, including those produced by the Z allele, can polymerize in hepatocytes leading to hepatocellular death, which can cause pediatric and adult-onset liver disease. It is unclear why an AAT deficiency in a newborn would cause FSP. Interestingly, previous cases have associated AAT deficiency and spontaneous pneumothorax in adults.9-11 However, it still remains uncertain whether the root cause of the pneumothorax in these cases was the AAT deficiency. Since a CT scan was not performed on the babies, there is no evidence of emphysema-like changes in the lungs. This raises the question: Could a non-antiprotease function of AAT lead to the observed FSP? AAT has been shown to play an antiapoptotic and antiinflammatory role in multiple organ systems.12-16 Thus, an increase in inflammation or apoptosis of the lung may encourage the development of FSP in the neonate.