TNFSF11 and cystic fibrosis: At baseline, markers of bone mass turnover and formation, such as osteocalcin, are reduced in the CF population compared to the non-CF population13–15 while the receptor activator of nuclear factor kappa-Β ligand (RANK-L), a marker of bone resorption, is elevated in the CF population at baseline when compared to the non-CF population13,16,17.