Olga R. Ismagilova

Background/Objectives: Friedreich’s ataxia in considered the most common form of autosomal recessive ataxia; however, it’s prevalence in the Russian Federation remains poorly studied. Methods: The study included 974 patient samples referred for analysis of the expanded GAA repeat in intron 1 of the FXN gene, as well as 319 healthy individuals participating in a biomaterial donation program for IVF, using PCR-AFLP and fragment analysis with labeled primers. Sanger sequencing of the FXN gene was additionally performed for six patients who exhibited a heterozygous expanded allele. Results: The diagnosis of FRDA was confirmed in 142 patients: 139 of them had homozygous GAA repeat expansions, the most common mutation type in this disorder, while in 3 cases a heterozygous expansion was associated with a pathogenic point mutation in the FXN gene on the second allele. For 28 probands, biallelic GAA expansions in FXN were subsequently confirmed in their affected relatives. Among the 319 healthy donors, only 2 carriers of a pathogenic expansion were identified. Conclusions: This paper presents the results of a long-term study on the molecular genetic causes of FRDA in Russian Federation, yielding an estimated frequency of 1:102,000 individuals for the disease associated with GAA repeat expansion.

The disruption of the epigenetic mechanisms of gene expression regulation due to the emergence of pathogenic variants in genes-encoding elements of epigenetic machinery leads to the development of chromatinopathies. This group of hereditary diseases includes 179 syndromes, some of which present with overlapping phenotypes. Despite the variety of approaches to molecular diagnostics of chromatinopathies, it is not always possible to establish the molecular diagnosis by traditional methods; thus, the issue of optimizing diagnostic algorithms remains relevant. One of the most rapidly expanding areas of post-genomic molecular diagnostics is episignature detection, which relies on genome-wide DNA methylation analysis. This article aims to represent an original approach to indirect diagnostics of chromatinopathies on the example of Rubinstein–Taybi syndrome 1, which is based on the analysis of the methylation level of a limited set of loci designed to reproduce its classic episignature. In the current study, we apply two methods of targeted quantitative analysis of DNA methylation, which are relatively accessible and can be integrated into diagnostic practice. We demonstrate that Rubinstein–Taybi syndrome 1 episignature may be successfully reduced to a single locus of human genome, and that quantitative bisulfite DNA methylation analysis at this locus allows accurate identification of the Rubinstein–Taybi syndrome 1 patients.

Клиническая и молекулярно-генетическая характеристика серии случаев синдрома Флоатинг-Харбор

Introduction: Rubinstein–Taybi syndrome (RSTS) is one of the many forms of syndromic intellectual disability, occurring in the population with a frequency of 1: 100–125 thousand newborns. The specific phenotype of patients enables the so-called “portrait” diagnosis of classical cases of RSTS, followed by the analysis of the CREBBP and EP300 genes, whose association with RSTS has been confirmed. Nevertheless, for approximately half of the patients in various cohorts, the diagnosis cannot be confirmed.Methods: In this paper we present the results of a study of 158 Russian patients referred for molecular diagnosis of RSTS using multiplex ligation-dependent probe amplification (MLPA) and next-generation sequencing (NGS).Results: Pathogenic and likely pathogenic variants were identified in 67 patients (42.4%), of which 62 (39%) were in CREBBP and 4 cases (2%)—in EP300. In one case, a known pathogenic variant in SRCAP, associated with Floating–Harbor syndrome (FHS), which is phenotypically similar to RSTS, was also identified; therefore, the possibilities and prospects for differential diagnosis were considered.

The androgen receptor (AR) is critical for mediating the effects of androgens. The polymorphic CAGn locus in exon 1 of the AR gene is associated with several diseases, including spinal and bulbar muscular atrophy (SBMA), prostate cancer, and male infertility. This study evaluated the CAGn locus in 9000 infertile Russian men and 286 fertile men (control group). The CAGn locus was analyzed using the amplified fragment length polymorphism method. In the infertile cohort, the number of CAG repeats ranged from 6 to 46, with a unimodal distribution. The number of CAG repeats in infertile and fertile men was 22.15 ± 0.93 and 22.02 ± 1.36, respectively. In infertile men, variants with 16 to 29 repeats were present in 97% of the alleles. A complete mutation (≥42 CAG repeats) was found in three patients, while three others had 39-41 repeats. The incidence of SBMA was 1:3000 infertile men. Significant differences (p < 0.05) were observed between infertile and fertile men in alleles with 21, 24 and 25 repeats. This study revealed certain differences in the CAGn polymorphic locus of the AR gene in Russian infertile and fertile men and determined the frequency of SBMA in infertile patients.

Pathogenic variants in the USH2A gene are the primary cause of both non-syndromic autosomal recessive inherited retinitis pigmentosa (RP) and the syndromic form, characterized by retinal degeneration and sensorineural hearing loss. This study presents a comparative assessment of the genetic variant spectrum in the USH2A gene among Russian patients in two clinical groups. A retrospective analysis was conducted on massive parallel panel sequencing data from 2415 blood samples of unrelated patients suspected of having hereditary retinal diseases. The copy number of USH2A exons was determined using the quantitative MLPA method with the MRC-Holland SALSA MLPA kit. Biallelic pathogenic and likely pathogenic variants in the USH2A gene were identified in 69 patients (8.7%). In the group of patients with isolated hereditary RP (55 patients), the most frequent pathogenic variants were p.(Glu4445_Ser4449delinsAspLeu) (20.9%), p.(Trp3955*) (15.5%), and p.(Cys934Trp) (5.5%). In patients with the syndromic form (14 patients), the most frequent variants were p.(Trp3955*) (35.7%) and c.8682-9A>G (17.9%). It was found that patients with isolated vision impairment rarely had two “null” variants (17.8%), whereas this was common among patients with both hearing and vision impairment (71.4%) (p ≤ 0.05), explaining the severity of the disease and the earlier onset of clinical symptoms in the syndromic form of RP. Ten previously undescribed loss-of-function variants were identified. The estimated prevalence of USH2A-associated retinal dystrophy in Russia was 1.9 per 100,000 individuals. The obtained data on the differences in the spectra of genetic variants in the USH2A gene in the two studied groups highlight the importance of establishing genotype–phenotype correlations and predicting disease severity, aiming at potential early cochlear implantation and selection of target therapy.

(1) Background: The androgen receptor (AR) is critical for mediating the effects of androgens. The polymorphic CAGn locus in exon 1 of the AR gene is associated with several diseases, including spinal and bulbar muscular atrophy (SBMA), prostate cancer, and male infertility. This study evaluated the CAGn locus in 9,000 infertile Russian men and 286 fertile men (control group); (2) Methods: The CAGn locus was analyzed using the polymorphism of lengths of amplified fragments method; (3) Results: In the infertile cohort, CAG repeats ranged from 6 to 46, with a unimodal distribution. The number of CAG repeats in infertile and fertile men was 22.15 ± 0.93 and 22.02 ± 1.36, respectively. In infertile men, variants with 16 to 29 repeats were present in 97% of alleles. A complete mutation (≥42 CAG repeats) was found in three patients, while three others had 39-41 repeats. The incidence of SBMA was 1: 3,000 infertile men. Significant differences (p<0.05) were observed between infertile and fertile men in alleles with 21, 24 and 25 repeats; (4) Conclusions: This study revealed certain differences in the CAGn polymorphic locus of the AR gene in Russian infertile and fertile men, and determined the frequency of SBMA in infertile patients.

Rubinstein-Teibi syndrome (RTS) is a multisystem pathology characterized by mental retardation and delayed physical development combined with characteristic external manifestations that make up a recognizable picture of the disease. The literature review highlights the clinical manifestations of RTS, considers the issues of geno-phenotypic correlations and differential diagnostics, describes the possibilities and prospects of diagnostics and treatment, taking into account the results of modern research.