Document is current

Article History

Received: 22 January 2020

Accepted: 2 June 2020

First Online: 10 June 2020

Ethics approval and consent to participate

: This study has been granted an exemption from requiring ethics approval according to “The ethics committee of Peking Union Medical College Hospital”.

: Not applicable.

: L M, Y G, H M, B Z and Q M declare that they have no competing interests.