I read with great interest the article by McShane and Glassroth in a recent issue of CHEST (December 2015). The authors cite the following as predisposing factors to the development of the nodular bronchiectasis phenotype of pulmonary disease due to Mycobacterium avium complex (NB-PMAC): genetic predisposition, body habitus, fibrillin abnormalities, mitral regurgitation, isolated CFTR gene mutation, and ciliary abnormalities. It is difficult to identify a pathway by which these factors might lead to its defining features, which include: disease confined to the lingula and/or middle lobe, female (largely postmenopausal) exclusivity, and absence of a predisposing pulmonary disorder. Genetic predisposition for an exclusively female disorder implies a sex linkage, which affects male subjects only. If a tall, lean habitus, mitral valve prolapse, and pectus excavatum are markers of an undefined, predisposing, connective tissue disorder, how might this account for susceptibility to these organisms and for the circumscribed localization? Why are male subjects with the referenced abnormalities in body habitus and mitral valve prolapse spared? Marfan’s syndrome, which is not associated with NB-PMAC, is the sole fibrillin malady with which I am acquainted. It has an autosomal dominant inheritance. The authors did not describe a pathway by which a CFTR gene mutation would predispose to NB-PMAC in the absence of clinical manifestations of cystic fibrosis. There is no gender preference for cystic fibrosis or ciliary abnormalities, both typically present in childhood, and neither exhibits circumscribed pulmonary involvement.