One promising fundamental area of research of genetics of complex diseases, related to the study of the genome variability of somatic cells in target organs was underlined in the review. The results of own research on the copy number variations and DNA methylation level in peripheral blood leukocytes and arterial cells in human atherosclerosis were shown. From a practical point of view, the identified molecular targets can be used as biomarkers for the prevention, diagnosis, and treatment of complex diseases.

Cytogenetic diagnosis performed only by GTG-staining does not provide sufficient reliability and accuracy in the identification of structurally rearranged chromosomes. To describe the karyotype in such cases, it is required to involve methods of molecular-cytogenetic analysis. The purpose of this study was to develop methods for testing, specification and correcting the results of primary cytogenetic diagnostics using complex methods of modern chromosomal analysis by two cases of patients with abnormal karyotypes. Separation and cultivation human peripheral blood lymphocytes, metaphase chromosome preparation, GTG-, CBG-, Ag-NOR-differential staining of chromosomes, chromosomal in situ suppression hybridization were done according to standard protocol. The creation of microdissection DNA probes and their quality control were performed as described previously. Chromosomes were counterstained with DAPI to visualize DNA after in situ hybridization. Inverted DAPI banding of chromosomes was used for chromosome identification, according to ISCN (2009). Using the GTG-, CBG-, Ag-NOR-staining of chromosomes, chromosomal in situ suppression hybridization with specially prepared microdissection DNA probes, the patient’s karyotype, previously described as 46,XX,der(4)t(4;?)(p12;?) or del(4)(p12p15.2), was determined as 46,XX,del(4)(p12p15.2), and the patient’s karyotype previously described as 47,XY,+22 was determined as 47,XY,+invdup(15)(q13). Applying methods of cytogenetic analysis, including methods of differential staining of chromosomes and fluorescent in situ hybridization with specially prepared DNA probes, allows to specify and, if necessary, to correct the description of the karyotype, resulting in accurate and reliable description of patient karyotypes. Clarification of the cytogenetic diagnosis is important for the medical-genetic predictions.

Introduction: Extensive chromosomal aberrations are often associated with psychomotor development delay, intellectual disability, and congenital malformations. Despite the high frequency of mutations and due to the involvement, as a rule, of several genes, as well as the wide variety of chromosomal abnormalities themselves, there are currently no ways to effectively treat such patients. Aim: To study spontaneous chromosomal instability in patients with ring chromosomes in differentiated and induced pluripotent stem cells (iPSC). Materials and methods: In patients with intellectual disability and developmental abnormalities, ring chromosomes 13 and 22 were identified during standard karyotyping. A number of additional chromosomal mutations in their karyotype were identified using Agilent 860K microarrays. FISH analysis confirmed ring chromosomes and found mosaicism for them in lymphocytes, fibroblasts, and iPSCs of the patients. iPSCs were obtained from skin fibroblasts by exogenous expression of transcription factors (KLF4, OCT4, SOX2, and human c-MYC). Results: Terminal 13q34 and 22q13.32-q13.33 deletions were identified in patients, resulting in the formation of ring chromosomes 13 and 22, respectively. FISH analysis confirmed the presence of ring chromosomes and found that 47% and 8% of lymphocytes of the patients had monosomies 13 and 22, respectively. At the first passage 50% and 24% of the fibroblasts were monosomic for chromosomes 13 and 22, respectively. On the 9^th passage 56% of fibroblasts demonstrated monosomy 13. Among the lymphocytes and fibroblasts at the 9th passage, 1.8% and 1% of the cells, respectively, had a normal karyotype. By the 33^rd passage, the number of fibroblasts with monosomy 22 reached 44% and statistically significantly exceeded the initial level ( P < 0.05). The proportion of iPSC monosomic for chromosome 22 varied between 6.3-17% for different clones. Conclusion: The presence of monosomic cells in patients with a ring chromosome indicates chromosomal instability already in vivo. In vitro a statistically significant increase in the number of cells with monosomy 22 is observed. Cells with normal karyotype can be evidence of chromosomal defect correction processes, which are the basis of the chromosomal therapy of genetic diseases that is beginning to be developed.

The role of CNV in pathogenesis of intellectual disability and autism is significant. Nevertheless, in the analysis of CNV-associated diseases, the interpretation of pathogenically significant CNV remains a debatable issue, while the mechanisms of the phenotypic manifestation of inherited CNVs and their incomplete penetrance remain largely unclear. At present, the incomplete penetrance of CNV is explained mainly from the point of view of allelic interactions of various genetic variants. At the same time, the epigenetic mechanisms of gene expression regulation in the context of structural genome variations remain practically unexplored. The purpose of this study was to search for differentially methylated CpG sites located in regions with inherited CNV in families with mental retardation and autism. As a result, differential methylation of intragenic CpG sites of the IMMP2L gene in the family of a patient with intellectual disability and 7q31.1 microdeletion was identified. The data obtained indicate the possibility of the involvement of DNA methylation in the regulatory mechanisms of incomplete penetration of CNV-associated diseases.

The structure of the gene pool of the indigenous population of Dagestan belonging to Andi language group of Nakh-Dagestani language family using STR markers was investigated. We used DNA population samples representing Andi, Akhvah, Bagulal, Botlikh, Godoberi, Karata, Tindi and Chamalals. All of the pairs of the compared samples demonstrated no statistically significant differences between the different population. The main features of the gene pool of the peoples of Dagestan are relatively high genetic diversity and a low level of genetic differentiation between ethnic groups.

Genetic structure of Khakass genera (seoks) using Y-chromosome markers was investigated. The results of the analyses of haplogroup frequencies and YSTR- haplotypes indicate that Khakass seoks are related associations, in most cases having the same ancestor in the patrilineage. The gene pool of Khakass, more precisely a part marked by Y-chromosome haplogroups, was shown to be primarily structured on a generic principle. A strong genetic affinity of the seok members was shown for the vast majority of the samples.

To date, more than 230 microdeletion and 80 microduplication syndromes were revealed in patients with intellectual deficiency and developmental delay. The fact that deletions predominate may be an indirect confirmation of the established opinion that microduplications are less pathogenic in case of a milder clinical manifestation. The aim of the study was to determine the frequency and spectrum of pathogenetically significant chromosomal microduplications among patients with disabilities of mental development, to estimate the ratio of clinically significant microdilutions and microdeletions in this group of patients. The sample consists of 216 patients aged 2 to 18 years: children with mental development disorders, and having dysmorphia and/or congenital anomalies. The search for chromosomal microduplications was carried out using matrix comparative genomic hybridization on microarrays (8х60K, Agilent Technologies). To confirm the segmental trisomy identified in the probands and determine their parental origin, a quantitative real-time PCR method was used. Among the detected pathogenetically significant variations in the number of copies of DNA regions registered in 81 patients with mental development disorders (37%), unbalanced translocations or combinations of different types of CNVs were identified in 9 patients, 2 patients were carriers of ring chromosomes 13 and 22, 70 patients were found with 36 deletions and 34 duplications, the ratio of which was 51% and 49% respectively. In the process of analyze of the origin of partial trisomy it was established that 8 cases (47%) of microduplication appeared de novo and 9 cases (53%) were inherited from phenotypically healthy parents. The frequency of clinical significant chromosomal microduplications in the group of patients with mental development disorders was 15,7%, microdeletions - 16,7%. Perhaps this confirms the underestimation of microduplications as a cause of the development of pathological conditions and points to the importance of their more detailed study.

Translocations involving an X chromosome and an autosome are rare and are associated with a variable phenotype. Most unbalanced X-autosomal translocations result in multiple abnormalities; a smaller proportion cause gonadal dysgenesis without other anomalies or mental retardation. We present clinical, cytogenetic and molecular cytogenetic findings of two patients with de novo unbalanced X-autosomal translocations with different phenotypic features which may be explained by the pattern of inactivation of the derivate chromosome X.