Footnotes

• Handling editor Tahir S Pillay.

• Contributors K-SP performed the laboratory tests and wrote the manuscript. ZHT and JHY performed the laboratory tests. ESCK advised on the study design and supervised the study and critically edited the manuscript. KT collected the clinical information and wrote the manuscript.

• Funding The authors have not declared a specific grant for this research from any funding agency in the public, commercial or not-for-profit sectors.

• Competing interests None declared.

• Patient consent for publication Not required.

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