Footnotes

• Contributors All authors made substantial contributions to the manuscript and approved the final draft. AK, SK and GO collected and analysed the data. AK wrote the first draft and GO conducted the major modifications of the manuscript. IY conducted and supervised the statistical analyses. YH cooperated with the data collection and analyses. AU and AC measured the antiganglioside antibodies. MS designed the whole study and finalised the manuscript.

• Funding Provided grants to support investigators.

• Competing interests None.

• Ethics approval The Ethics Committee of the Teikyo University School of Medicine.

• Provenance and peer review Not commissioned; externally peer reviewed.