The manuscript by King et al. 1 in this issue of the European Respiratory Journal raises the possibility that mutations in the cystic fibrosis (CF) transmembrane conductance regulator (CFTR) may be responsible, at least in part, for low bone density in CF cohorts. More than 100 publications from around the globe, the majority in the last decade, have described low bone density in CF adult and, to a lesser extent, paediatric populations. The pathogenesis, epidemiology, clinical manifestations, and preventative and therapeutic options have all been discussed previously 2. While the primary clinical correlates of low bone density in CF have previously been measures of lung function, body mass index and corticosteroid use 2, the good work of King et al. 1 has, for the first time, reported a direct link with ΔF508 (the major disease-causing mutation of the CFTR consisting of deletion of phenylalanine 508). While others have looked for this association in the past without success 3–5, the work of King et al. 1 does raise some very interesting possibilities.
The fundamental question is: do mutations in CFTR cause low bone density and, if so, what are the mechanisms ( via direct channel functions, interaction with other ion channels or other means). This editorial will concentrate almost exclusively on this topic, since other aspects of CF bone disease have been explored in detail elsewhere. The most likely, albeit not the only, link between bone health and CFTR may be found in the gut, kidney, parathyroid glands or bone. A discussion about the well-known effects of pancreatic insufficiency on fat-soluble vitamin absorption and their role in bone mineralisation is excluded here. The most important issue is whether chloride channels, which are numerous in type and expressed almost ubiquitously in all tissues types, are linked to a …