Authors' contributions
WFY
Both authors read and approved the final manuscript. WFY and HDZ contributed to the study concept and design, revising the manuscript for important intellectual content, and approval of the final version to be published. KJX, JYC and LLT contributed to acquisition of data, analysis and interpretation of data, drafting the manuscript, and approval of the final version to be published. FLG and JF contributed to analysis and interpretation of data. ZXH and YFP contributed to acquisition of data and interpretation of data.