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Central precocious puberty (СPP) is caused by premature reactivation of the hypothalamic–pituitary–gonadal axis. Genetic, epigenetic, and environmental factors play a crucial role in determining the timing of puberty. In recent years, the KISS1, KISS1R, MKRN3, and DLK1 variants have been identified as hereditary causes of CPP. The MKRN3 and DLK1 genes are imprinted, and therefore epigenetic modifications that alter the expression of these genes are also considered as a cause of precocious puberty. With the progression of CPP, epigenetic factors such as DNA methylation, posttranslational modifications of histones and noncoding RNAs can mediate the relationship between the influence of genetic variants and the environment. CPP is also associated with other short- and long-term adverse health effects. This is the basis for research aimed at understanding the genetic and epigenetic causes of СPP. The purpose of this review is to summarize the published data on the molecular genetic and epigenetic mechanisms of the formation of СPP. [ABSTRACT FROM AUTHOR]

Genomic imprinting is an epigenetic phenomenon that differentiates maternal and paternal copies of genes in the genome and causes monoallelic expression depending on parental origin. Imprinting is an evolutionary puzzle, as it bears the costs of diploidization without its advantages, namely, protection from recessive mutations. The aim of this review is to answer the question of why genomic imprinting arose and became fixed in the evolution of angiosperms, insects, marsupials, and placental mammals. [ABSTRACT FROM AUTHOR]

Differential gene expression during development is maintained by complex regulatory epigenetic mechanisms that provide the formation of different specialized cell types. Subsequently, a multicellular organism is a mosaic of cells with differing epigenetic characteristics. It seems likely that exceeding the limits of normal epigenetic variability may cause the occurrence of pathological mosaic states in which one part of the cell population has a normal epigenotype, while the other part carries modified epigenetic information. In this review, using the genomic imprinting as a classical epigenetic phenomenon, for the first time, the prevalence of epigenetic mosaicism and the mechanisms of its origin, as well as its role in the etiology of hereditary disorders, determined by the dysfunction of imprinted genomic loci are summarized. [ABSTRACT FROM AUTHOR]

A great amount of copy number variations (CNVs) are identified in the human genome. Most of them are neutral; nevertheless, the role of CNVs in the pathogenesis of hereditary diseases is still significant. Especially, this is important for neuropsychiatric disorders, such as intellectual disability and autism. When analyzing the CNV-associated diseases, the controversial question is to distinguish the pathogenic CNVs among common polymorphic variants and to predict the disease risk in other children of the family. Unfortunately, the mechanisms of phenotypic expression and incomplete penetrance of CNVs remain largely unknown. Currently, incomplete penetrance and variable expressivity of CNVs are attributed mainly to allelic interaction of different genetic variations. However, epigenetic mechanisms of gene expression regulation in the context of structural variation of the genome are poorly explored. It is possible that epigenetic modifications of the genome regions with CNVs may underlie the understanding of ways of phenotypic manifestations of structural variations in the human genome. [ABSTRACT FROM AUTHOR]

An analysis of differential methylation of 47 imprinted genes in placenta tissues of spontaneous abortions at the first trimester of pregnancy from women with recurrent pregnancy loss or with one sporadic abortion was performed using the DNA-microarray approach. We showed that epimutations of the imprinted genes were registered significantly more often in abortions from women with recurrent miscarriage in contrast to the embryos from women with sporadic pregnancy loss with frequency of 6.2 and 3.7% per locus, respectively (p < 0.01). The predominant type of epimutation appeared to be a postzygotic hypomethylation of the imprinted genes on chromosomes of maternal origin, which was observed in the examined samples in 5.1 and 2.89% of cases, respectively. Replicative study of the methylation status of seven imprinted genes ( DLK1, PEG10, PLAGL1, KCNQ1OT1, PEG3, GRB10, and PEG1/MEST) in the enlarged embryo samples supported the results of microarray analysis in respect to both epimutation frequency and predominance of somatic hypomethylation of maternal alleles. It was also demonstrated that pregnancy loss was associated with multilocus methylation defects of imprinted genes, the frequency of which was also significantly increased in the placental tissues of spontaneous abortions in women with recurrent miscarriage. [ABSTRACT FROM AUTHOR]

LINE-1 retrotransposon is the most common mobile genetic element in the genomes of various mammals, including humans. Its genes are represented by the greatest number of copies. For a long time, it has been considered that the presence of LINE-1 in genome reflects the limited ability of cells to eliminate it, and the retrotransposon activity is negative owing to the insertional mutagenesis. In recent years, the increased expression of LINE-1 retrotransposon and the activity of their encoded proteins observed in mammalian cells at different stages of development and, first of all, in early embryogenesis have been discussed in the literature. Is early embryogenesis the stage of development when the organism is more susceptible to the activity of retrotransposons, or does LINE-1 play some positive role in early embryonic development? This review is aimed at classifying the available data on the epigenetic regulation and the role of LINE-1 retrotransposon in embryogenesis of mammals. The link between the mechanisms of regulation of LINE-1 expression and the waves of epigenetic reprogramming is tracked in germ cells, during fertilization, and in blastocyst, as well as during the differentiation of embryonic and extraembryonic tissues. [ABSTRACT FROM AUTHOR]

Early stages of human embryonic development are characterized by the spatiotemporal coincidence of events of total epigenetic genome reprogramming and elevated level of mosaic forms of numerical chromosome abnormalities. It is possible that the abnormal reprogramming of various regions of the genome can lead to violations of local epigenetic chromatin organization and gene expression, which affect the correct chromosome segregation during mitosis. In this study, a comparative analysis of the methylation index of LINE-1 retrotransposon, which largely reflects the methylation profile of the genome, is performed in placental tissues of spontaneous abortions with complete and mosaic forms of aneuploidy and with a normal karyotype, as well as in the control group of induced abortions of the first trimester of pregnancy. It was shown that extraembryonic mesoderm and chorionic cytotrophoblast of spontaneous abortions with chromosomal mosaicism are characterized by the highest index of LINE-1 methylation among all studied groups. At the same time, the excessive hypomethylation of transposable genetic element was registered in spontaneous abortions with normal karyotype. We hypothesize that violations of parental genome demethylation during epigenetic reprogramming at preimplantation stages of development may be associated with an increased frequency of mitotic errors in chromosome segregation, which leads to the formation of a mosaic karyotype. [ABSTRACT FROM AUTHOR]

The contribution of chromosomal abnormalities to recurrent pregnancy loss (RLP) is reviewed in the paper. Data from conventional cytogenetic analysis of the karyotype of parents and spontaneous abortions, as well as the results of molecular cytogenetic investigations and preimplantation genetic diagnostics, are discussed. Information about the significance of epigenetic impairments (abnormalities of imprinting and X-chromosome inactivation) for recurrent pregnancy loss is also considered. Cytogenetic analysis of products of conception enables ascertainment of the causes of embryonic death in a large proportion of families, more accurate estimation of the therapeutic efficiency of treatment and drugs (when women with abnormal embryos were excluded), and a statistically valid prognosis about the next pregnancy outcome. [ABSTRACT FROM AUTHOR]

The current knowledge on multiple epimutations in imprinted genes and their impact on the disturbance of human prenatal development and the emergence of hereditary diseases are reviewed and analyzed. Genetic mechanisms regulating the epigenetic state of imprinted loci in the human genome are discussed. [ABSTRACT FROM AUTHOR]

The methylation profiles of the placental tissues of human embryos with normal karyotype and trisomy 16 were compared using an Infinium HumanMethylation27 BeadChip array (Illumina, United States). Numerous differences between the extraembryonic tissues with diploid and aneuploid karyotypes were observed. The extraembryonic mesoderm of embryos with trisomy 16 appeared to be less methylated than the diploid tissue, whereas the cytotrophoblast of aneuploid embryos was hypermethylated. The presence of the supernumerary chromosome was shown to influence the epigenetic profile of the genome by changing the level of methylation of CpG sites of all chromosomes. However, the largest number of differentially methylated loci was found on chromosome 16. Furthermore, more often, the epimutations were tissuespecific. In both tissues, the hypomethylated genes belong to the groups of genes responsible for different metabolic processes, whereas the hypermethylated genes control the processes of development, cell adhesion, immune response, and response to stimulus. [ABSTRACT FROM AUTHOR]