Pathogenic variants in the SLC26A4 gene (OMIM #605646), leading to non-syndromic recessive hearing loss type 4 (DFNB4) and Pendred syndrome, significantly contribute to the etiology of hearing loss in many populations of the world. The spectrum and prevalence of different pathogenic SLC26A4 variants are characterized by wide ethno-geographical variability. A high frequency of some of them in certain regions of the world may indicate either their independent origin or be a consequence of the founder effect. The proportion of SLC26A4-associated hearing loss in Tuvinian patients (the Tyva Republic, Southern Siberia) is one of the highest in the world (28.2 %) and the vast majority of mutant SLC26A4 alleles are represented by three pathogenic variants c.919-2A>G, c.2027T>A and c.1545T>G (69.3, 17.5 and 8.0 %, respectively). Their overall carrier frequency in the Tuvinian population reaches 7.1 %. The accumulation of these variants in Tuvinian patients suggests a role of the founder effect in their prevalence in Tuva, which can be confirmed by the common genetic background (haplotypes) for each of them. For reconstruction of haplotypes in the carriers of variants c.1545T>G and c.2027T>A, the genotyping data of a panel of polymorphic genetic markers were used: five STRs (four of them flank the SLC26A4 gene at different distances and one is intragenic) and nine intragenic SNPs. Comparative analysis of the reconstructed haplotypes for c.1545T>G and c.2027T>A with previously obtained data on haplotypes for the c.919-2A>G variant showed that each of the analyzed variants has a specific (similar for all carriers of a particular variant) genetic background, apparently inherited from different “founder ancestors”. These data confirm the cumulative founder effect in the prevalence of pathogenic variants c.1545T>G, c.2027T>A, and c.919- 2A>G of the SLC26A4 gene in the indigenous population of the Tyva Republic. The obtained data are relevant both for predicting the prevalence of SLC26A4-caused hearing loss and for development of region-specific DNA diagnostics of inherited hearing loss in the Tyva Republic.

ABSTRACTIt was evidenced, that the increase in the prevalence of autosomal recessive deafness 1A (DFNB1A) in populations of European descent was promoted by assortative marriages among deaf people. Assortative marriages become possible with a widespread introduction of sign language resulting in increased the genetic fitness of deaf individuals, thus relaxing selection against deafness. Currently, cochlear implantation is becoming a common method of rehabilitation for deaf patients, restoring their hearing ability and promoting the acquirement of spoken language. Whether the mass cochlear implantation could affect the spread of hereditary deafness is unknown. We have developed an agent-based computer model for analysis of the spread of DFNB1A. Using the model, we tested impact of different intensity of selection pressure on an isolated human population for 400 years. The modeling of the “purifying” selection pressure on deafness resulted in decrease of the proportion of deaf individuals and the pathogenic allele frequency. The modeling of relaxed selection resulted in increase of the proportion of deaf individuals and the decrease of the pathogenic allele frequency. The results of neutral selection pressure modeling showed no significant changes in both the proportion of deaf individuals and the pathogenic allele frequency after 400 years. Thus, initially low genetic fitness of deaf people can be significantly increased in the presence of assortative mating by deafness, resulting in a higher prevalence of DFNB1A. Contrary, frequency of pathogenic allele and the incidence of hereditary hearing loss will not increase in a population where all deaf individuals undergo cochlear implantation.

В работе приводятся результаты комплексной оценки патогенетической значимости нового варианта с.516G>C (p.Trp172Cys) гена GJB2, выявленного с высокой частотой у больных с потерей слуха из Республик Тыва и Алтай (Южная Сибирь). Совокупность полученных данных свидетельствует в пользу ассоциации этого варианта с наследственной глухотой вследствие его повреждающего эффекта на структуру и функционирование белка коннексина 26 (Cx26). We present the results of a complex assessment of the pathogenetic significance of novel variant c.516G>C (p.Trp172Cys) of the GJB2 gene found with high frequency in deaf patients from the Tyva and Altai Republics. Several lines of evidences support pathogenicity of this variant due to its damaging effect on the structure and functioning of connexin 26 (Cx26).

В работе представлены результаты молекулярно-генетических исследований врожденной формы катаракты (CTRCT18, MIM 610019), распространенной в Якутии. We present the results of molecular genetic studies of the congenital cataract (CTRCT18, MIM 610019) common in the Sakha Republic of Russia.

На основе материалов тотальной переписи населения (2010 г.) проведен анализ распространенности языка жестов в России. Полученные результаты сопоставлены с имеющимися данными о частоте наследуемых форм потери слуха на территории России. The paper presents the results of an analysis of the prevalence of sign language (SL) in Russia collected during the 2010 total census, as well as their comparison with data on the frequency of hereditary forms of hearing loss.

Мутации в гене SLC26A4 являются частой причиной потери слуха во многих регионах мира. В работе приводятся результаты молекулярно-генетического анализа (с использованием секвенирования по Сэнгеру) последовательности гена SLC26A4, впервые проведенного в выборке пациентов с потерей слуха неустановленной этиологии (n=232) из Республик Тыва и Алтай. Установлены контрастные различия патогенетического вклада мутаций в гене SLC26A4 в этиологию нарушения слуха у коренных жителей этих географически близких регионов: 28,2% - для тувинцев и 4,3% - для алтайцев. Выявлены как уже известные, так и новые патогенные варианты, а также широкий спектр полиморфных вариантов гена SLC26A4. Mutations in the SLC26A4 gene are a common cause of hearing loss in many regions of the world. This paper presents the results of molecular genetic analysis (by Sanger sequencing) of the SLC26A4 sequence, first performed in the sample of patients with hearing loss of unknown etiology (n=232) from the Tyva Republic and the Altai Republic. Contrast differences of the pathogenic contribution of SLC26A4 mutations to the etiology of hearing impairment were revealed in the indigenous peoples of these geographically close regions: 28.2% for Tuvinians and 4.3% for Altaians. Both known and novel pathogenic variants as well as a wide range of polymorphic variants were found in the SLC26A4 gene sequence.

We present the results of analysis of skin epidermis thickness in individuals with recessive mutation c.-23+1G>A in the GJB2 gene in comparison with individuals without this mutation living in Eastern Siberia (Yakut population). We examined 152 individuals with different genotypes by GJB2 gene mutation c.-23+1G>A . Homozygotes and heterozygotes by c.-23+1G>A have thicker epidermal layer (0.245 mm and 0.269 mm, respectively) in comparison with individuals without this mutation (0.193 mm) ( p <0.05). The obtained data support the hypothesis about selective advantage of carriers of mutant GJB2 gene alleles and partly explain extremely high carrier frequency (10.3%) of c.-23+1G>A mutation in the GJB2 gene in Yakut population in Eastern Siberia.

Наиболее частой причиной несиндромальной потери слуха являются мутации гена GJB2. Ранее было показано, что в Якутии вклад мутаций гена GJB2 в потерю слуха среди пациентов с врожденной тугоухостью составил 49%. Целью данной работы являлся поиск молекулярно-генетических основ потери слуха среди GJB2-негативных пациентов, у которых причина заболевания осталась неустановленной. В исследование были включены 238 (228 неродственных) GJB2-негативных пациентов, среди которых мы обнаружили одну семью с 5 пораженными индивидами с ювенильной потерей слуха неизвестной этиологии (дебют заболевания варьировал от 0 до 8 лет). Путём полноэкзомного анализа (WES), проведенного у одного из пораженных членов семьи, была выявлена ранее не описанная гомозиготная замена c.1121G>A в 6-ом экзоне гена CLIC5 (6p21.1, OMIM 607293). Данная транзиция приводит к образованию преждевременного стоп-кодона в 374-ой аминокислотной позиции (p.Trp374*), терминирующего синтез полипептидной цепи белка CLIC5 (NP_001107558.1). В гене CLIC5 известна только одна гомозиготная замена c.96T>A (р.Cys32*), которая ранее была найдена в инбредной турецкой семье с постлингвальной прогрессирующей аутосомно-рецессивной глухотой (DFNB103). В настоящей работе гомозиготный вариант c.1121G>A (p.Trp374*) был выявлен у 26 из 238 GJB2-негативных пациентов (10,9%). У большинства из них (19 из 26) отмечается поздний дебют потери слуха в среднем в 9,7±0,6 лет. Аудиологическое обследование у 13 из 26 пациентов выявило преимущественно симметричную сенсоневральную прогрессирующую потерю слуха различной степени тяжести (от донозологической и I-ой степени тугоухости до глухоты). Распространенность DFNB103, обусловленной гомозиготным вариантом c.1121G>A (p.Trp374*) гена CLIC5, в Якутии составила в среднем 0,27±0,05 на 10000 человек с максимальным накоплением в Эвено-Бытантайском национальном районе (31,39±10,46 на 10000 человек), который относится к арктической группе улусов, где большинство населения составляют эвены (53%). Это первый в России случай идентификации орфанного заболевания, накопление которого обнаружено в Арктике. В целом, гомозиготный вариант c.1121G>A (p.Trp374*) гена CLIC5 можно расценивать как каузативный для DFNB103 с высоким вкладом в этиологию нарушений слуха у населения Якутии. The most common cause of non-syndromic hearing loss in various populations of the world is the mutations in the GJB2 gene. Previously it was shown that the pathogenic contribution of the GJB2-mutations among patients with congenital hearing loss in Yakutia was 49%. The aim of this work was to investigate the molecular genetic basis of hearing loss among GJB2-negative patients. The study included 238 (228 unrelated) GJB2-negative patients, among them we found one family with five affected individuals with juvenile hearing loss of unknown etiology (the disease onset varied from 0 to 8 years). Using a whole exome sequencing (WES), performed in one of affected family members, a novel homozygous c.1121G>A (6p21.1, OMIM 607293) substitution in exon 6 of the CLIC5 gene was detected. This substitution leads to the formation of a premature stop codon at the 374 amino acid position (p.Trp374*) which terminates the synthesis of the polypeptide chain of the CLIC5 protein (NP_001107558.1). To date, only one homozygous mutation c.96T>A (p.Cys32*) was known in human gene CLIC5 which was found in one inbred Turkish family with progressive autosomal recessive deafness, type 103 (DFNB103). In our study, a homozygous variant c.1121G>A (p.Trp374*) was detected in 26 out of 238 GJB2-negative patients in Yakutia (10.9%). Most of homozygous for c.1121G>A patients (19 out of 26) reported about late onset of their hearing loss occurred in postlingual period (averaged 9.7±0.6 years). Audiological examination of 13 out of 26 patients revealed predominantly symmetric sensorineural progressive hearing loss of varying severity (from mild to profound hearing loss). The average prevalence of DFNB103 caused by the homozygous variant c.1121G>A (p.Trp374*) in Yakutia was 0.27±0.053 per 10000 with a maximum accumulation in Eveno-Bytantaysky district (31.39±10.46 per 10000) which referred to the Arctic group of districts where the majority of the population is represented by Evens (53%). This is the first case of the identification of the orphan disease with its accumulation in Arctic part of Russia. In general, the homozygous variant c.1121G>A (p.Trp374*) of the CLIC5 gene can be regarded as causative to DFNB103 with a high contribution to the etiology of hearing impairments in the population of Yakutia.

Autosomal recessive deafness type 1A (DFNB1A) caused by mutations in the GJB2 gene (Cx26) is the main cause of nonsyndromic hearing impairment in many populations worldwide. It is considered that widespread prevalence of DFNB1A can be due to the long tradition of intermarriages between deaf people (assortative marriages) combined with their increased social adaptation and genetic fitness after widespread introduction of sign language. For the first time, the data on mating structure and reproduction of deaf people living in Yakutia (Eastern Siberia, Russia) are presented in comparison with contribution of the GJB2 gene mutations to the etiology of hearing impairment. The relative fertility of deaf people compared to their hearing siblings is 0.78 (mean number of children 1.76 ± 0.10 and 2.24 ± 0.09 to deaf and their hearing siblings, respectively, p = 0.0018). The rate of assortative marriages among deaf people is 77.1% (81 of 105 marriages). Biallelic mutations in the GJB2 gene were found in 42.2% (43 of 102) of examined deaf people, which corresponded to diagnosis DFNB1A for these patients. A comparison of deaf marital partners by GJB2 status revealed a proportion of noncomplementary marriages (24%) in which hearing loss in both partners was caused by the presence of biallelic GJB2 gene mutations resulting in the birth of only deaf children in such couples. Thus, the set of obtained data including a relatively high genetic fitness (expressed as relative fertility) of deaf people in Yakutia in combination with a high rate of assortative marriages among them and high incidence of DFNB1A indicates a possible weakening of selection against such trait as “deafness” and a possible increase in the frequency of GJB2 mutant alleles in subsequent generations.

In this paper we present for the first time the results of the audiological and clinical-genealogical research of the population of settlements Batagai-Alyta and Kustur of the Eveno-Bytantaisky National District (ulus) of the Sakha Republic (Yakutia) for studying the postlingual form of deafness of unknown etiology firstly identified by us earlier in 3 Evens. As a result of an audiological examination of 72 people, 10 patients from 6 nuclear families who met the criteria of postlingual form of hearing loss were found. The segregation analysis carried out in these families confirmed the autosomal recessive type of inheritance of this form of postlingual hearing loss. The distant relationship of the examined patients with postlingual hearing loss living in two villages of the Eveno-Bytantaisky National District of the Sakha Republic can indicate to the role of the founder effect in the local prevalence of this pathology.

The high carrier frequency of c.-23+1G>A mutation in the GJB2 gene in Yakut population is might be explained not only by the factors of population dynamics (founder effect, genetic drift, small effective population size), but also can be due to the selective advantage of heterozygous mutations in the GJB2 gene. Because the GJB2 gene is expressed not only in the cochlea but also in other tissues, and in vitro studies conducted on cell cultures show that GJB2-mutant cells were more resistant to the infection of dysentery - Shigella flexneri. The aim of this study is the analysis of the resistance in heterozygous carriers of the c.-23+1G>A mutation in GJB2 gene to diarrhea. Material and methods. We examined 272 Yakut individuals, which was divided into two groups: the first group consisted from 238 individuals without c.-23+1G>A mutation, the second group consisted from 34 individuals with c.-23+1G>A mutation in heterozygous state. All respondents independently filled information about the number of cases of diarrhea in the last year, and indicated the most characteristic form of their stool. Results and Discussion. In heterozygous carriers of the c.-23+1G>A mutation the cases of diarrhea in the last year were not registered in 22% of individuals, in individuals without mutation cases of diarrhea were not registered in 5% of individuals. According to the results of this study heterozygous carriers of the c.-23+1G>A mutation statistically significantly are less susceptible to diarrhea cases than individuals without this mutation. Thus, the obtained results can support the hypothesis about selective advantage of the GJB2 gene mutant alleles carriers and partly explain the extremely high carrier frequency (10.3%) of the c.-23+1G>A mutation in the GJB2 gene in Yakut population.