Cystic fibrosis (CF) is a complex multisystem genetic disease, with pulmonary and gastrointestinal consequences dominating the clinical picture. The life-expectancy of CF patients has increased through several therapeutic advances. Although respiratory failure remains the major cause of mortality in CF, musculoskeletal impairments contribute to major morbidity. In the general population, musculoskeletal conditions are among the most common reasons for seeking medical care, and the risk of osteoporotic fracture increases with age. As the CF population ages, the morbidity related to musculoskeletal effects may increase.

The etiology of CF related bone disease is multifactorial and includes effects of pancreatic insufficiency, poor nutritional status, vitamin D deficiency, glucocorticoid treatment, inflammation, hypogonadism, and sarcopenia, collectively resulting in attenuated bone mineral accrual and low bone density The effect of cystic fibrosis transmembrane conductance regulator (CFTR) modulating drugs on bone disease in CF has not been evaluated. Effects of CFTR modulators may help counter the bone and muscle consequences of CF either directly by effects on bone or muscle cells, or indirectly by improved lung disease, improved nutritional status, decreased systemic inflammation or glucocorticoid use, or subsequent increases in physical activity.

The rationale that underlies the proposed research is that better understanding of the bone and muscle effects of CFTR modulator therapies will help guide strategies to optimize bone accrual, prevent osteoporosis and fractures, and improve functional outcomes in the aging CF population. Set on the backbone of a longitudinal observational cohort study, the study will systematically and comprehensively evaluate changes in bone and muscle mass and strength from baseline to 12 month and 24 month time points among patients receiving CFTR modulator therapies and also among controls not receiving CFTR modulator therapies.