Author contribution: Obrubov SA – academic advising, data acquisition, literature analysis; Markelova SV – data acquisition, statistical processing, literature analysis, manuscript writing.

Compliance with ethical standards: the study was approved by the Ethics Committee of Pirogov Russian National Research Medical University (protocol No. 159 dated November 21, 2016). The informed consent was obtained for all the participants. The study met the requirements of biomedical ethics and involved no risk to participants.