Selected microRNAs as Potential Diagnostic Biomarkers in Polycystic Ovary Syndrome in Adolescent Girls  
[PERSON]  
1 Department of Pediatrics, Medical University of Varma, 9002 Varma, Bulgaria; [EMAIL_ADDRESS] (S.G.); [EMAIL_ADDRESS] (V.I) Department of Biochemistry, Molecular Medicine and Nutrigenomics, Medical University of Varma, 9000 Varma, Bulgaria; [EMAIL_ADDRESS] (Correspondence: [EMAIL_ADDRESS]: Tel.: +359-886606985 1255988606985 12559860698  
self-perpetuating vicious circle [5; 6]. The clinical presentation of PCOS evolves with age from ovulatory dysfunction (menstrual irregularities, anovulation) and hyperandrogenism (hirsutism, severe acne), frequently associated with obesity and metabolic disturbances (insulin resistance, hyperinsulinemia, dyslipidemia), to a mainly metabolic disorder with obesity, insulin resistance, impaired glucose metabolism, dyslipidemia and increased cardiovascular risk [7]. Impaired fertility, obstetric complications and psychological issues are common, and an increased cancer risk has been reported [7; 8].  
The current criteria for diagnosis of PCOS in adolescents include the presence of clinical and/or biochemical hyperandrogenism (HA) and oligomenorrhea/secondary amenorhea (OA), after exclusion of other hyperandrogenic endocrine disorders (congenital adrenal hyperplasia, androgen producing tumors, etc.) [1]. These diagnostic criteria are controversial because they overlap with common physiological changes typical of puberty [9]. This creates the prerequisites for both late and inaccurate diagnosis, and overdiagnosis with adverse late consequences in terms of quality of life [10]. Therefore, in recent years, much work has been carried out for the detection of new biomarkers with high specificity and sensitivity, which would help clarifying the pathogenetic mechanism of PCOS, earlier establishing the diagnosis and monitoring the therapy.  
MicroRNAs (miRNAs) are endogenous small non-coding single-stranded RNA molecules with 20-25 nucleotides, found in various environments--plasma and serum, ovarian granulosa cells and follicular fluid, seminal fluid, urine, etc. They inhibit the expression of the target messenger RNA and block the post-transcriptional protein translation [11]. MiRNAs regulate a number of processes, growth, cell differentiation and dedifferentiation, apoptosis, hormone biosynthesis, hematopoiesis, etc., and because of their stability are used as biomarkers for different diseases [11]. In the ovaries, miRNAs are involved in the regulation of proliferation and apoptosis of granulosa cells, growth and atresia of follicles, ovulation, luteinization and steroidogenesis. They are also important for the metabolic aspects in the pathogenesis of PCOS [12]. Different studies report many differently expressed miRNAs in PCOS. Some of them correlate with PCOS-related comorbidities--insulin resistance (miR-320, miR-93) and obesity (miR-197-3p, miR-223-3p, miR-877-5p, miR-122-5p). Others are significantly down-regulated (miR-451a, miR-6767-5p, miR-103a-3p, etc.) or up-regulated (miR-21-5p, miR-23a-3p, miR-26a-5p, etc.) in women with PCOS compared to controls, making them suitable for diagnostic biomarkers for PCOS [12; 13; 14; 15].  
The aim of the current study was to explore the plasma levels of selected miRNAs in adolescent girls with PCOS, healthy controls and controls with HA, but not fulfilling the diagnostic criteria for PCOS in adolescence (HAC) with evaluation of their suitability as diagnostic biomarkers for PCOS or predictors of PCOS-related comorbidities. As a secondary outcome of the study, we looked for correlations with the typical clinical, hormonal and metabolic characteristics of PCOS.