. Authors-'contributions, . Nb, . Co, . Pn, . Bcv et al., NB and BCV wrote the paper; PN and JMT had primary responsibility for final content. All authors read and approved the final manuscript. 10-17 kg 1, pp.40-70

W. Gahl, J. Thoene, and J. Schneider, Cystinosis, New England Journal of Medicine, vol.347, issue.2, pp.111-121, 2002.
DOI : 10.1056/NEJMra020552

W. Gahl, J. Balog, and R. Kleta, Nephropathic Cystinosis in Adults: Natural History and Effects of Oral Cysteamine Therapy, Annals of Internal Medicine, vol.147, issue.4, pp.242-250, 2007.
DOI : 10.7326/0003-4819-147-4-200708210-00006

M. Stachowicz, B. Lehmann, A. Tibi, P. Prognon, V. Daurat et al., Determination of total cysteamine in human serum by a high-performance liquid chromatography with fluorescence detection, Journal of Pharmaceutical and Biomedical Analysis, vol.17, issue.4-5, pp.767-773, 1998.
DOI : 10.1016/S0731-7085(97)00248-3

E. Belldina, M. Huang, J. Schneider, R. Brundage, and T. Tracy, Steady-state pharmacokinetics and pharmacodynamics of cysteamine bitartrate in paediatric nephropathic cystinosis patients, British Journal of Clinical Pharmacology, vol.270, issue.5, pp.520-525, 2003.
DOI : 10.1046/j.1365-2125.2003.01927.x

L. Smolin, K. Clark, J. Thoene, W. Gahl, and J. Schneider, A Comparison of the Effectiveness of Cysteamine and Phosphocysteamine in Elevating Plasma Cysteamine Concentration and Decreasing Leukocyte Free Cystine in Nephropathic Cystinosis, Pediatric Research, vol.23, issue.6, pp.616-620, 1988.
DOI : 10.1203/00006450-198806000-00018

B. Chadefaux-vekemans, White cell cystine group: guideline n°2. Polymorphonuclear leucocyte preparation, BIMDG bulletin, 2001.

A. Chabli, J. Aupetit, M. Raehm, and D. Ricquier, Measurement of cystine in granulocytes using liquid chromatography-tandem mass spectrometry, Clinical Biochemistry, vol.40, issue.9-10, pp.692-698, 2007.
DOI : 10.1016/j.clinbiochem.2007.02.005

E. Kuhn and M. Lavielle, Maximum likelihood estimation in nonlinear mixed effects models, Computational Statistics & Data Analysis, vol.49, issue.4, pp.1020-1038, 2005.
DOI : 10.1016/j.csda.2004.07.002

R. Savic and M. Karlsson, Importance of Shrinkage in Empirical Bayes Estimates for Diagnostics: Problems and Solutions, The AAPS Journal, vol.11, issue.3, pp.558-569, 2009.
DOI : 10.1208/s12248-009-9133-0

B. Anderson and N. Holford, Mechanism-Based Concepts of Size and Maturity in Pharmacokinetics, Annual Review of Pharmacology and Toxicology, vol.48, issue.1, pp.303-332, 2008.
DOI : 10.1146/annurev.pharmtox.48.113006.094708

R. Ihaka and R. Gentleman, R: A Language for Data Analysis and Graphics, Journal of Computational and Graphical Statistics, vol.5, pp.299-314, 1996.
DOI : 10.1080/10618600.1996.10474713

R. Pisoni, G. Park, V. Velilla, and J. Thoene, Detection and Characterization of a Transport System Mediating Cysteamine Entry into Human Fibroblast Lysosomes: SPECIFICITY FOR AMINOETHYLTHIOL AND AMINOETHYLSULFIDE DERIVATIVES, Journal of Biological Chemistry, vol.270, issue.3, pp.1179-1184, 1995.
DOI : 10.1074/jbc.270.3.1179