Funding: the study was supported as part of the State Assignment of the Research Centre for Medical Genetics and the Ministry of Health of the Republic of North Ossetia–Alania.

Author contribution: Zinchenko RA, Tebieva IS, Gabisova YuV, Khokhova AV — patient examination, making the diagnosis, obtaining the informed consent, and biomaterial collection; Shukan EYu — acquisition of data on the number of patients; Zinchenko RA, Tebieva IS, Kutsev SI — study planning, statistical analysis, manuscript writing; Marakhonov AV — analysis of molecular genetic tests; Tebieva IS, Marakhonov AV, Zinchenko RA — editing; Zinchenko RA, Kutsev SI — general management, editing.

Compliance with ethical standards: the study was approved by the Ethics Committee of the Research Centre for Medical Genetics (protocol No. 5 dated 20 December 2010), it was compliant with the Good Clinical Practice and evidence-based medicine standards. All patients submitted the informed consent to participation in the study.