Propionic acidemia is a rare autosomal recessive metabolic disorder, characterized as classic organic acidemia. The article represents biochemical and molecular characterization of 16 patients diagnosed with propionic acidemia in Russia. Symptoms appeared during the first months after birth in most cases. Poor feeding, seizures, hypotonia, lethargy were the most frequent symptoms. Biochemical tests (GC-MS and MS/MS) showed elevated 3-hydroxypropionic acid, methylcitrate, propionylglycine, C3 in patients blood. Six undescribed earlier variants were found as a result of PCCA & PCCB (4 variants - PCCA, 2 - PCCB) genes DNA-tests. Variant c.655-2A>G in PCCB is the most frequent in this group (17.2%). Localization of missense variants and their effect on protein was demonstrated using propionyl-CoA carboxylase 3D model. New variants were classified according to the American College of Medical Genetics and Genomics (ACMG) guidelines.

Earlier, in Yakutia, using whole exome sequencing (WES) the genetic cause of juvenile autosomal recessive deafness (DFNB103, OMIM 616042), caused by the nonsense variant c.644G>A p.(Trp215*) of the CLIC5 gene, was identified. This work presents the results of the analysis of the carrier frequency of the variant c.644G>A p.(Trp215*) in 512 adult individuals without hearing impairment from 8 populations of Eastern Siberia (Russians, Russian old-timers, Yakuts, Evenks, Evens, Dolgans, Yukaghirs and Chukchi). With the highest carrier frequency this mutation was found in the Yukaghir population (3.2%), with intermediate carrier frequencies in Evens (1.4%) and Evenks (1.4%), with the lowest carrier frequency in Yakuts (0.8%) and was absent in Russians (including Russian old-timers), Dolgans and Chukchi. The analysis of haplotypes obtained as a result of genotyping of ~ 730,000 SNP-markers was carried out in 18 patients of various ethnic origins (Evens, Evenks, and Yakuts) homozygous for the c.644G>A p.(Trp215*) mutation, and 83 individuals without this mutation. All 18 individuals with the homozygous variant c.644G>A p.(Trp215*) showed homozygosity blocks of different lengths on chromosome 6, which were absent in the control group. All blocks overlapped in one region, 785.5 kb in length (224 SNP), which is evidence in favor of a single origin of the c.644G>A p.(Trp215*) mutation. Estimation of the age of c.644G>A-haplotypes showed that the expansion of mutant chromosomes could begin in the Late Neolith period (Bronze or Early Iron Age), and most likely not in the Turkic peoples, but in the Tungus-speaking, Ural-speaking, or even in paleoasians peoples. The data obtained indicate the relevance of the targeted analysis of the c.644G>A p. (Trp215*) mutation of the CLIC5 gene in the target groups of patients, among the indigenous population of Siberia and East Asia, and possibly among the populations of the Arctic coast of Eurasia and North America.

In the diagnosis of hereditary non-syndromic hearing loss (HL), the methods of molecular genetic analysis of the GJB2 (Cx26) gene mutations provide high valuable information. For the first time, in the Republic of Buryatia (Eastern Siberia), the spectrum and frequency of GJB2 gene mutations were determined in a sample of 165 individuals with HL using sequencing of significant regions of the GJB2 gene. A total of 13 known allelic variants were found (c.-254C>T, c.-49G>A, c.-23+1G>A, c.35delG, c.79G>A, c.101T>C, c.109G>A, c.235delC, c.299_300delAT, c.327_328delinsA, c.341A>G, c.457G>A u c.516G>C). In the sample of Buryat patients, the mutation spectrum was represented by five GJB2 variants: c.-23+1G>A (4.1%), c.109G>A (0.6%), c.235delC (1.4%), c.327_328delGGinsA (0.6%), c.516G>C (0.6%). Five mutations were found among Russian patients: c.35delG (25.7%), c.-23+1G>A (3.3%), c.109G>A (1.9%), c.101T>C (0.6%), c.299_300delAT (0.6%). In general, the contribution of biallelic mutations of the GJB2 gene to the etiology of HL in the total sample of patients in Buryatia was 15.8% (26/165). When the total sample of patients was divided by ethnicity the contribution of biallelic mutations of the GJB2 gene to the etiology of HL in Buryat patients was 5.1% (4/79), and in Russian patients - 28.9% (22/76). Thus, the results of our study indicate that the mutations in the GJB2 gene are not the main cause of HL in Buryats. Probably, in some GJB2-negative patients (84.2% in our study), HL may be due to the mutations in other genes responsible for the development of hereditary hearing impairments.

Hereditary cardiomyopathies are characterized by the generally poor prognosis and low 5-year survival of patients with severe symptoms. Besides surgical approaches, cardiomyopathy therapy mainly palliative and often heart transplantation is the only option to improve patient state and prognosis. Some of these pathologies are associated with the autosomal-dominant DES gene mutations. DES encodes intermediate filaments protein desmin, which defects causes desminopathies involving most active muscles such as skeletal muscles, myocardium and respiratory muscles. New therapeutic based on genome editing approaches could be used to correct causative genetic defect. There are data that heterozygous nonsense mutations in DES gene may be asymptomatic. Thus there is, apparently, a possibility to decrease severity of desminopathy using mutant allele knockout. Purpose. The aim of this work was to test the possibility of specific knockout of the DES gene alleles with heterozygous desminopathy-associated mutations by means of genome editing methods. Materials. We received genetic materials of three patients with desminopathy caused by DES gene mutations (c.330_338del, p.A337P (c.1009G>C) и p.R355P (c.1064G>C)). Guide RNA, compatible with nucleases SaCas9 and eSpCas9(1.1) were designed using online service Benchling and cloned into plasmids with corresponding Cas9 nucleases. Editing plasmids were cotransfected into HEK293T cells with “target” plasmids, containing DES gene sites with mutations. NHEJ-produced indels were assessed using TIDE-analysis with amplified and sequenced sites or using T7E1 analysis. Results. Combination sgRNA for c.330_338del with eSpCas9(1.1) demonstrated most mean efficiency of 2,22% (up to 8,06%). Others combinations of sgRNAs and Cas9 efficiency did not overcome 3%. Conclusions. Achieved knockout efficiency is evidently not enough for organism-level desminopathy correction. The need for specific knockout of mutated alleles does not allow usage of different guide RNAs for CRISPR/Cas9, so it is necessary to improve the developed systems to increase their efficiency or to use new, more efficient, targeted nucleases.

Developmental delay (DD) and intellectual disability (ID) are frequent reasons for referring patients for medical genetic counseling. A significant increase in the number of nosological forms of monogenic and chromosomal diseases among patients with DD or ID in medical genetic consultation of Bochkov Research Centre for Medical Genetics in recent years reflects an increase in its effectiveness in diagnosing this pathology. Purpose of the research: 1. To estimate the proportion of clinically and/or laboratory-confirmed chromosomal, monogenic, and genomic imprinting disorders diagnosed in patients with DD or ID consulted by geneticists from the consultation and scientific consulting departments of the Bochkov Research Centre for Medical Genetics in 2006, 2007, 2016, and the first half of 2017. 2. Determination of the effectiveness of different diagnostic methods of genetic forms DD and ID. 3. Calculation of segregation frequency to estimate the contribution of monogenic forms with autosomal recessive and X-linked recessive types of inheritance among undifferentiated cases of DD and ID. The sampling for the analysis included 2350 patients with DD or ID of varying severity, as well as patients with a diagnosis suggesting the development of DD or ID as they mature, consulted by geneticists from the consultation and scientific consulting departments of the Bochkov Research Centre for Medical Genetics in 2006, 2007, 2016, and the first half of 2017. During the research period (2006, 2007, 2016, and the first half of 2017), there was a decreasing trend in the proportion of chromosomal pathology among all patients of the sampling. Within the group of patients with DD or ID with chromosomal pathology, a significant increase in the proportion of structural chromosomal pathology and a decrease in the proportion of diseases caused by changes in the number of chromosomes is noted over time. The proportion of monogenic forms remains practically unchanged during the study period. Within this group, there is some increase in the share of AD pathology. The proportion of patients with DD or ID caused by genomic imprinting disorders varies significantly in the years studied, with a tendency to decrease over time. The proportion of only clinically identified syndromes without laboratory confirmation decreases significantly during the study period. The maximum diagnostic efficiency among laboratory genetic methods has been shown for microsatellite analysis, MLPA, chromosomal microarray analysis (CMA) and next generation sequencing (NGS).

The prevalence of rare chromosomal abnormalities (CAs) has not yet been reliably determined. This task can be accomplished by registering cases of rare CAs among fetuses, live births and stillborn in population-based registries of congenital malformations that exist in most countries of the world. According to the epidemiological register of the Moscow region for the period from 2011 to 2019, the prevalence rate of rare CA was 0,49 cases per 1000 births, their share in the structure of all CA is 11,3%. In percentage terms, the structure of rare CAs is presented as follows: triploidy - 41.2%, deletions - 23.9%, unbalanced translocations - 10.6%, rare trisomies - 6%, duplications - 5.6%, marker chromosomes - 3.7%, other rare CAs - 9%. Taking into account the international data, we can assume that the obtained prevalence rate of rare CAs is underestimated due to their underreporting and insufficient diagnosis in the studied region, which requires further research.