Author contribution: Milushkina OYu, Timerzyanov MI — academic advising, manuscript writing; Dubrovina EA, Khaertdinova LA — data acquisition, statistical processing, literature analysis.

Compliance with ethical standards: the study was approved by the Ethics Committee of the Pirogov Russian National Research Medical University (protocol No. 159 dated November 21, 2016). The informed consent was obtained for all participants. Participation in the study did not endanger the safety of individuals and met the requirements of biomedical ethics.