1. Department of Pediatrics, Peking University First Hospital, No. 1, Xi-an-men Road, Xicheng District, Beijing 100034. Tel: 008610-66551122 ext 3003; fax: 008610-66134261;
2. Department of Pediatrics, Peking University First Hospital, Beijing, China
3. Department of Pediatrics, Shimane University School of Medicine, Izumo, Japan