Present address for Hai-Lan YAO: Capital Inslitute of Paedialrics, 2 Yabao Rd, Beijing 100020, China; for Jin ZHANG: Ocean University of China, 5 Yushan Rd, Qingdao 266003, Shandong, China; for Xin-Li XIAO: School of Medicine, Xi'an Jiaotong University, Xi'an 710061, Shaanxi, China. Correspondence should be addressed to Xiao-Ping DONG, Tel: 86-10-83534616. Fax: 86-10-63532053. E-mail: dongxp238@sina.com Biographical note of the first author: Yan-Jun GUO, female, born in 1973, majoring in neurology.