1. Department of Developmental Medical Sciences, Institute of International Health, Graduate School of Medicine; The University of Tokyo; Bunkyo-ku Tokyo 113-0033 Japan
2. Kon-Kuk University; Chung Ju Hospital; Chungchongbuk-Do 380-701 Korea
3. Seoul National University Children's Hospital; Korea
4. Kawasaki City Institute of Public Health; Kawasaki Kanagawa 210-0834 Japan