Osteoporosis is a complex disease that is affected by a variety of factors, including genetic and epigenetic influences. While DNA markers for osteoporosis have been identified, they do not fully explain the hereditary basis of the disease. Epigenetic factors, such as small microRNAs (miRNAs), may provide a missing link in understanding the molecular mechanisms underlying osteoporosis. miRNAs are a class of non-coding RNAs that play a role in the epigenetic regulation of gene expression. They are known to be involved in various biological processes, including bone formation and remodelling. Differential expression of miRNAs has been linked to the pathological decrease in bone mineral density associated with osteoporosis. It has been shown that an abnormal miRNA expression pattern leads to a decrease in osteoblast activity and an increase in osteoclast activity. Further research into the role of miRNAs in osteoporosis may help to better understand this disease and identify potential therapeutic targets for treatment. Based on these assumptions, the study of miRNA expression patterns in osteoblasts, osteoclasts, and their precursors under normal and osteoporotic conditions is a rapidly growing field of scientific research. Although the results of this research are still incomplete and sometimes contradictory, they require additional scientific analysis to better understand the complex mechanisms involved. The purpose of this paper is to review the current research on miRNAs specifically expressed in osteoblasts and osteoclasts under both normal and pathological conditions. We will also discuss the potential applications of these miRNAs as biomarkers for osteoporosis diagnosis and as targets for osteoporosis treatment.

Multiple endocrine neoplasia syndrome type 1 (MEN-1) is an inherited disorder associated with mutations in the MEN1 gene and characterized by the «classic triad»: involvement of the parathyroid gland, pancreatic islet cells and anterior pituitary. The penetrance of primary hyperparathyroidism (PHPT) in MEN-1 reaches 90-100% with age. Primary hyperparathyroidism in MEN-1 is associated with polyglandular lesions, and tumors do not always develop synchronously, leading to a high incidence of disease recurrence after surgery. In MEN-1-associated PHPT, hyperplasia is most common and multiple adenomas are less common. The growth of hyperplastic cells may be diffuse, nodular or diffuse-nodular, which complicates the differential diagnosis between adenoma and diffuse-nodular hyperplasia with the presence of a single dominant nodule. Carcinomas and atypical tumors in MEN-1 are casuistically rare. We present the unique case of a young patient with a germline mutation in the MEN1 gene (c.684dup) and clinically «aggressive» course of PHPT due to atypical parathyroid tumors.