Footnotes

• Contributors ER designed and performed experiments, analysed data and wrote the manuscript. BL performed experiments and analysed data. SB, GN and CMR designed experiments and analysed data. PC provided serum samples for Variété controls. XM designed experiments, analysed data and revised the manuscript.

• Funding We thank the French Society of Rheumatology which provided financial support.

• Competing interests None declared.

• Ethics approval Local Ethic Committee of Hôpital Bichat and the ‘Comission Nationale informatique et Liberté’ in 2006.

• Provenance and peer review Not commissioned; externally peer reviewed.

• Data sharing statement All the authors in this current work declare that there are no unpublished data and that all data have been presented in the current manuscript.