1. Department of Pediatrics , Dokkyo Medical University School of Medicine , Shimotsuga , Tochigi , Japan
2. Department of Pediatrics , Nasu Red Cross Hospital , Ohtawara , Tochigi , Japan
3. Center for Research Collaboration and Support, Comprehensive Research Facilities for Advanced Medical Science, Dokkyo Medical University , Mibu , Tochigi , Japan
4. Department of Public Health , Dokkyo Medical University , Mibu , Tochigi , Japan