Author contributions
All authors had access to the data and a role in writing this manuscript. The authors fulfill the ICMJE Criteria for Authorship. Yoshihiro Nakamura wrote the initial draft. Kazuhiro Asada, Masashi Toyama, and Yoshiro Fujita reviewed the manuscript and provided critical intellectual input. All authors read and approved the submitted draft of the manuscript.
Acknowledgements: We thank Dr Waka Kokuryo for making constructive comments and for providing encouragement.