Footnotes

• Contributors HF contributed to the acquisition of data, study design, statistical analyses, interpretation of data, drafting/revising of the manuscript for intellectual content and gave final approval. KPN contributed to the acquisition of data, interpretation of data, drafting/revising of the manuscript for intellectual content and gave final approval. JT contributed to analysis of the blood samples, drafting/revising of the manuscript for intellectual content and gave final approval. LL contributed to the study design, analysis of blood samples, drafting/revising of the manuscript and gave final approval. RJC and TTY contributed to acquisition of data, drafting/revising of the manuscript for intellectual content and gave final approval. NK contributed to the study design, statistical analysis, interpretation of the data, drafting/revising of the manuscript and gave final approval.

• Funding This research was supported by the Ministry of Health Healthcare Research Scholarship, Master of Clinical Investigation, Singapore and National Neuroscience Institute, Singapore.

• Competing interests None declared.

• Patient consent Obtained.

• Ethics approval SingHealth Institutional Ethics Review Board.

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