Designing Clinical Trials in "Regular" COPD Versus Alpha-1 Antitrypsin Deficiency-Associated COPD: "More Alike Than Unalike?".

Alpha-1 antitrypsin deficiency (AATD) predisposes to emphysema, liver disease, and panniculitis. This emphysema risk naturally invites a comparison between "regular" chronic obstructive pulmonary disease (COPD) (i.e., unrelated to AATD) and AATD-associated emphysema. Several features characterize both conditions. Both can be life-limiting and highly debilitating. Both are highly under-recognized. An important corollary of this comparison between "regular" COPD and AATD-associated COPD is whether both should be treated similarly and whether clinical trials to assess new therapies can be conducted similarly in both. Here, the distinctions between "regular" COPD and AATD-associated COPD are quite pronounced. Therapeutically, sparse available data suggest that lung volume reduction surgery confers less improvement in forced expiratory volume in 1 second (FEV1) in AATD and that such benefits are shorter-lived. Perhaps the most striking contrast between the 2 conditions is that clinical trial designs and conduct are necessarily very different. The relative scarcity of diagnosed individuals with AATD hampers recruitment to trials. Furthermore, primary outcome measures in trials of "regular" COPD must differ markedly from those of AATD-associated emphysema. Specifically, power calculations show that FEV1 and exacerbation frequency, which are amply represented as endpoints in large COPD trials, are infeasible in studies of AATD-associated emphysema. Rather, in the 3 available randomized controlled trials of intravenous augmentation therapy, the rate of emphysema progression based on serial computed tomography densitometry measurements has been the only feasible primary outcome measure. These considerations underscore the distinctive challenges and needs of conducting treatment trials in AATD-associated emphysema and emphasize that, with regard to clinical study design, the 2 conditions are "more unalike than alike."