SERPINA1 and alpha 1-antitrypsin deficiency: The EXACTLE (EXAcerbations and CT scan as Lung Endpoints) trial [13] was undertaken to explore the role of CT densitometry as a potential primary outcome measure in the setting of a double-blind, placebo-controlled study of the effect of alpha 1-antitrypsin (AAT) augmentation therapy on the progression of emphysema in individuals with AATD (PiZ) over 24 to 30 months.