Cystic fibrosis (CF) is a common monogenic disease caused by pathogenic variants in the CFTR gene. The distribution and frequency of CFTR variants vary in different countries and ethnic groups. The spectrum of pathogenic variants of the CFTR gene was previously studied in more than 1,500 CF patients from different regions of the European and North Caucasian region of Russia and the spectrum of the most frequent pathogenic variants of the CFTR gene and ethnic features of their distribution were determined. To assess the population frequency of CFTR gene mutations some of the common variants were analyzed in the samples of healthy unrelated individuals from the populations of the European part of the Russian Federation: 1,324 Russians from four European regions (Pskov, Tver, Rostov, and Kirov regions), representatives of five indigenous ethnic groups of the Volga-Ural region [Mari (n = 505), Udmurts (n = 613), Chuvash (n = 780), Tatars (n = 704), Bashkirs (n = 517)], and six ethnic groups of the North Caucasus [Karachay (n = 324), Nogais (n = 118), Circassians (n = 102), Abazins (n = 128), Ossetians (n = 310), and Chechens (n = 100)]. The frequency of common CFTR mutations was established in studied ethnic groups. The frequency of F508del mutation in Russians was found to be 0.0056 on average, varying between four regions, from 0.0027 in the Pskov region to 0.0069 in the Rostov region. Three variants W1282X, 1677delTA, and F508del were identified in the samples from the North Caucasian populations: in Karachay, the frequency of W1282X mutation was 0.0092, 1677delTA mutation – 0.0032; W1282X mutation in the Nogais sample – 0.0127, the frequency of F508del mutations was 0.0098 and 1677delTA – 0.0098 in Circassians; in Abazins F508del (0.0039), W1282X (0.0039) and 1677delTA (0.0117) mutations were found. In the indigenous peoples of the Volga-Ural region, the maximum frequency of the F508del mutation was detected in the Tatar population (0.099), while this mutation was never detected in the Mari and Bashkir populations. The E92K variant was found in Chuvash and Tatar populations. Thus, interethnic differences in the spectra of CFTR gene variants were shown both in CF patients and in healthy population of the European and North Caucasian part of Russia.

The distribution and frequency of the CFTR gene mutations vary considerably between countries and ethnic groups. Russians are an East Slavic ethnic groups are native to Eastern Europe. Russians, the most numerous people of the Russian Federation (RF), make about 80% of the population. The aim is to reveal the molecular causes of CF in ethnic Russian patients as comprehensively as possible. The analysis of most common CFTR mutations utilized for CF diagnosis in multiethnic RF population accounts for about 83% of all CF-causing mutations in 1384 ethnic Russian patients. Variants c.1521_1523delCTT (F508del), c.54-5940_273+10250del21kb (CFTRdele2,3), c.2012delT (2143delT), c.2052_2053insA (2184insA), and c.3691delT (3821delT) are most typical for CF patients of Russian origin. DNA of 154 CF patients, Russian by origin, in whom at least one mutant allele was not previously identified (164 CF alleles), was analyzed by Sanger sequencing followed by the multiplex ligase-dependent probe amplification (MLPA) method. In addition to the 29 variants identified during the previous test for common mutations, 91 pathogenic CFTR variants were also revealed: 29 missense, 19 nonsense, 14 frame shift in/del, 17 splicing, 1 in frame ins, and 11 copy number variations (CNV). Each of the 61 variants was revealed once, and 17 twice. Each of the variants c.1209G>C (E403D), c.2128A>T (K710X), c.3883delA (4015delA), and c.3884_3885insT (4016insT) were detected for three, c.1766+1G>A (1898+1G>A) and c.2834C>T (S945L) for four, c.1766+1G>C (1898+1G>C) and c.(743+1_744-1)_(1584+1_1585-1)dup (CFTRdup6b-10) for five, c.2353C>T (R785X) and c.4004T>C (L1335P) for six, c.3929G>A (W1310X) for seven, c.580-1G>T (712-1G>T for eight, and c.1240_1244delCAAAA (1365del5) for 11 unrelated patients. A comprehensive analysis of CFTR mutant alleles with sequencing followed by MLPA, allowed not only the identification of 163 of 164 unknown alleles in our patient sample, but also expansion of the mutation spectrum with novel and additional frequent variants for ethnic Russians.

BackgroundPrimary microcephaly represents an example of clinically and genetically heterogeneous condition. Here we describe a case of primary microcephaly from the Karachay-Cherkess Republic, which was initially diagnosed with Seckel syndrome.Case presentationClinical exome sequencing of the proband revealed a novel homozygous single nucleotide deletion in ASPM gene, c.1386delC, resulting in preterm termination codon. Population screening reveals allele frequency to be less than 0.005. Mutations in this gene were not previously associated with Seckel syndrome.ConclusionsOur case represents an additional support for the clinical continuum between Seckel Syndrome and primary microcephaly.

Molecular testing for mutations in the connexin 26 gene (GJB2) is a routine diagnostic analysis for subjects with hereditary hearing loss worldwide. However, till now there is no assessment of the diagnostic sig nificance of this analysis for Russian patients, and there are difficulties in interpretation of the results of DNA diagnostics. In the present study, a sample of 705 patients with nonsyndromic autosomal recessive hearing loss from different regions of Russian Federation was investigated. A portion of DFNB1 hearing loss caused by mutations in the GJB2 gene among the sample was 46%. The frequency of DFNB1 hearing loss was 1:1000, that is, the frequency of isolated autosomal recessive hearing loss 1:500 in the population. It was found that each sixteenth individual in Russia is a heterozygous carrier of the mutation in the GJB2 gene. Totally, 20 pathological GJB2 alleles were detected; among them, a c.35delG mutation with the allelic frequency 81% prevails. Six most frequent mutations (c.35delG, c.313_326del14, c.23+1G>A (IVS1+1G>A), c.235delC, c.167delT, and p.Glu120del), which account for 95% of pathological GJB2 alleles, were detected. Mutations previously not described in the GJB2 gene (c.129delG, p.Gly200Arg, and c[Arg127His, Gly160Ser]) were found. An optimal algorithm of molecular testing of Russian patients which detects up to 100% of mutations in the GJB2 gene was suggested.

Prevalence and allelic heterogeneity of hereditary diseases (HDs) could vary significantly in different human populations. Current knowledge of HDs distribution in populations is generally limited to either European data or analyses of isolated populations which were performed several decades ago. Thus, an acknowledgement of the HDs prevalence in different modern open populations is important. The study presents the results of a genetic epidemiological study of hereditary diseases (HDs) in the population of the Karachay-Cherkess Republic (KChR). Clinical screening of a population of 410,367 people for the identification of HDs was conducted. The population surveyed is represented by five major ethnic groups—Karachays, Russians, Circassians, Abazins, Nogais. The study of the populations was carried out in accordance with the proprietary protocol of genetic epidemiological examination designed to identify >3500 HDs easily diagnosed during clinical examination by qualified specialists specializing in the HDs. The protocol consists of the population genetic and medical genetic sections and is intended for comprehensive population analysis based on the data on different genetic systems, including the genes of HDs, DNA polymorphisms, demographic data collected during hospital-based survey. 8950 families (with 10,125 patients) with presumably the HDs were initially identified as a result of the survey and data collection through various sources of registration (from 1156 medical workers from 163 medical institutions). A diagnosis of hereditary pathology was established in 1849 patients (from 1295 families). Two hundred and thirty nosological forms were revealed (in 1857 patients from 1295 families). The total prevalence of HDs was 1:221. Differences between populations and ethnic groups were identified: 1:350 in Russians, 1:195 in Karachays, 1:199 in Circassians, 1:218 in Abazins, 1:135 in Nogais. Frequent diseases were determined, the presence of marked genetic heterogeneity was identified during the confirmatory DNA diagnosis. To explain the reasons for the differentiation of populations by load of HD, a correlation analysis was carried out between the FST (random inbreeding) in populations and HDs load values. This analysis showed genetic drift is probably one of the leading factors determining the differentiation of KChR populations by HDs load. For the first time, the size of the load and spectrum of HDs in the populations of the KChR are determined. We have demonstrated genetic drift to be one of the main factors of the population dynamics in studied population. A significant genetic heterogeneity of HDs, both allelic and locus, was revealed in KChR.