1. Department of Pediatrics, Obihiro Kosei Hospital, Nishi 6-jo Minami 8-1, Obihiro, Hokkaido 080-0016, Japan
2. Okurayama-gakuin, 20-2 Miharashi-cho, Otaru, Hokkaido 047-0263, Japan
3. Department of Hematology, Obihiro Kosei Hospital, Nishi 6-jo Minami 8-1, Obihiro, Hokkaido 080-0016, Japan