1 Department of Rheumatology, Beijing Children's Hospital, Capital Medical University, National Centre for Children's Health, No. 56 Nan Li Shi Lu, Beijing, 100045, China.
2 Department of Rheumatology, Beijing Children's Hospital, Capital Medical University, National Centre for Children's Health, No. 56 Nan Li Shi Lu, Beijing, 100045, China. caifeng_li@yeah.net.