Nephropathic Cystinosis (NC) is an orphan inherited autosomal recessive disease characterised as a generalized lysosomal storage disease due to a deficiency of the cystine lysosomal transport protein, cystinosin. Patients with NC usually receive cysteamine. Bone impairment was recently recognized as a late complication of NC, occurring at adolescence or early adulthood. Even though the exact underlying pathophysiology is unclear, at least six hypotheses are discussed, and mainly cysteamine toxicity and/or direct bone effect of the Cystinosin (CTNS) mutation. Because of the potential dramatic impact on quality of life of this novel complication, research should aim to better understand bone disease in NC. The primary objective of this study is to evaluate the action of cysteamine on osteoclastic differentiation and resorption activity of NC patients, depending on the underlying genotype. The Secondary objective is to describe the clinical bone status of NC patients depending on their underlying genotype.