Funding for this research was provided by:
National Natural Science Foundation of China (No. 81271890)
Capital Health Research and Development of Special (No.2016-2-2026)
Beijing Municipal Science & Technology Commission (No.Z161100000116088)
Received: 21 November 2018
Accepted: 26 June 2019
First Online: 12 July 2019
Ethics approval and consent to participate
: This study was approved by the Medical Ethics Committee of Beijing Friendship Hospital, Capital Medical University (No. 2015-P2–022-01). Written informed consent was obtained from parents of each underaged participant.
: Not applicable.
: The authors declare that they have no competing interests.