Malfunction of the gene coding for the CF transmembrane conductance
regulator (CFTR) protein causes defective cAMP-dependent chloride secretion from the epithelium
of different exocrine tissues, leading to thick viscous and difficult-to-clear
secretions in lungs, sinuses, pancreas, intestine, liver, and reproductive tract. In
addition, the CFTR-mediated regulation of sodium channel activity may fail, leading to
increased sodium absorption from the airways, which contributes to the fluidity and mobilization of
the airway secretions. Also, hyperplastic airway epithelium with areas of erosion and
squamous metaplasia of the submucosal glands leads to plug of mucoid material and subsequently
to the release of inflammatory cells. Eventually, grossly dilated airways with purulent secretions
are observed and severely congested parenchyma develops. Radiologic findings reflect the pathologic changes in the airways. Although the lungs of infants born with CF
are structurally normal at birth, respiratory symptoms are usually the first sign of CF.