The aim of the study is to look for risk factors of developing osteoporosis in patients with cystic fibrosis.

Blood cells called monocytes will be obtained from a blood sample. These monocytes will make possible to form another class of cells called osteoclasts in the laboratory. These latter cells are responsible for bone degradation and therefore promote the increase of bone fragility. The research will focus on the characterization of these cells to better understand their potential (low, medium or high) to increase bone fragility in patients with cystic fibrosis.

Finally the action of CFTR modulators on these bone cells will be tested.

The aim of the study is to characterize the profile of circulating monocytes as predictive biomarker of osteoclastogenesis in CF related bone disease.

Investigators will evaluate the presence and regulation of CD115 (MCSF receptor) and CD265 (RANK) membrane receptors of circulating monocytes of cystic fibrosis patients.

They will also analyze the impact of the F508del CFTR mutation on the differentiation of monocytes into osteoclasts. We will 1) Quantify the training and functional activity of osteoclasts and, 2) Test in vitro the effects of correctors and potentiators of CFTR on the resorption activity of differentiated osteoclasts.

The study will be explained to patients and they only will have one blood test.

Inclusion Criteria:

• patients with cystic fibrosis
• attending the Paris Cochin adult CF centre
• with at least F508del mutation (homozygote or heterozygote patients)

Exclusion Criteria:

• patients younger than 18
• absence of signed consent
• patients without a F508del mutation