Cystic Fibrosis Related Bone Disease: the Role of CFTR

COHORT 1 Inclusion Criteria: * Age 6 to 75 years old * Established diagnosis of CF with at least one abnormal G551D-CFTR allele * Eligibility for and intent to start treatment with ivacaftor or started treatment with ivacaftor within previous 6 months Exclusion Criteria: * Psychiatric or mental incapacity that would preclude subject from assenting to study participation * Current pregnancy * History of organ transplantation * History of Burkholderia dolosa infection COHORT 2: Subjects will be grouped by gender, age and race to match subjects in Cohort 1 within two years. Pubertal subjects will be matched by Tanner stage. Inclusion Criteria: * Age 6 to 75 years old * Established diagnosis of CF Exclusion Criteria: * Psychiatric or mental incapacity that would preclude subject from assenting to study participation * Current pregnancy * History of organ transplantation * History of Burkholderia dolosa infection COHORT 3: Subjects will be grouped by gender, age and race to match subjects in Cohort 2 within two years. Pubertal subjects will be matched by Tanner stage. Inclusion criteria: * Age 6 to 75 years old * Clinically stable, deemed able to complete the screening, baseline, and scheduled study visits. Exclusion criteria: * History of significant cardiac, renal, pulmonary, hepatic, or malignant disease, current alcohol or illicit drug abuse, or major psychiatric disorder * Current diagnoses known to affect bone metabolism, including cystic fibrosis, osteoporosis, amenorrhea \>3 months (in menstruating women who are not taking oral contraceptives or have an IUD), hyperthyroidism, diabetes, hyperparathyroidism, Paget's disease, kidney stones, chronic inflammatory diseases, malabsorptive disorders, malnutrition, prolonged immobility, and skeletal dysplasias * History of a non-digital fracture in the previous 6 months, history of one pathologic fracture, or greater than four total lifetime non-digital fractures * Cumulative lifetime use of oral glucocorticoids for greater than 2 months * Current or prior use of medications known to affect bone metabolism including hormone replacement therapy, anti-estrogens, bisphosphonates, calcitonin, fluoride, lithium, suppressive doses of levothyroxine, or anticonvulsants. * Pregnancy * BMI less than 18.5 or greater than 30 kg/m2 in subjects 18 years and older, or BMI less than 5th or greater than 95th percentile in subjects under the age of 18 years. * Any medical or psychiatric condition or situation that would compromise subject safety, informed consent/assent, treatment compliance, follow-up measurements, or data quality