In an earlier study with a smaller sample size, OPG concentrations were increased in CF compared with both DP and HP, and the ratio of OPG/RANKL was decreased in CF compared with DP and HP in the acute phase.35 Additionally, there are no significant differences in in vivo gene expression of RANKL or OPG.8 These contradicting findings could result from differences in acuteness of CF presentation. The gene discussed is TNFRSF11B; the disease is cystic fibrosis.