Noonan syndrome (NS) and related RASopathies form a clinically and genetically heterogeneous group of disorders caused by germline dysregulation of the RAS/MAPK pathway. Pathogenic variants in PTPN11 account for roughly half of classical NS, but the contribution of non-PTPN11 genes in patients referred with NS or Noonan-like phenotypes remains incompletely defined in several populations, including Russia. We characterized the spectrum of non-PTPN11 variants in a large Russian cohort referred for suspected NS or Noonan-like phenotypes and examined gene-specific clinical patterns. We analyzed 456 unrelated patients with clinically diagnosed NS or Noonan-related syndromes using a targeted panel of 23 RAS/MAPK pathway genes. PTPN11 variants (23% of cases) were reported previously; here we focused on the remaining patients. Pathogenic or likely pathogenic variants were identified in 19% of cases (85/456), with NF1, SOS1, SHOC2, and BRAF being the most frequently mutated genes, together accounting for 50% of the non-PTPN11 diagnoses. Novel variants were observed in 12.1% of cases (7/58 unique variants). Several genotype-phenotype associations emerged: SOS1 mutations were associated with a high prevalence of cardiac defects, especially pulmonary stenosis and atrial septal defects (64% of patients, p = 0.01), whereas NF1 and SPRED1 cases had significantly fewer cardiac anomalies (p < 0.001 and p < 0.05, respectively). Lentigines were predominantly seen in NF1 and SPRED1 patients (p < 0.01), and all three evaluable males with MAP2K1 variants had cryptorchidism (3/3). Conversely, BRAF-mutated patients showed lower incidence of chest deformity (p < 0.01) but higher rates of developmental delay. NF1, SOS1, SHOC2, and BRAF together accounted for half of the non-PTPN11 molecular diagnoses in this Russian cohort, and the observed gene-specific clinical patterns align with previous series, although limited subgroup sizes preclude firm individual associations.

BACKGROUND:Developmental and epileptic encephalopathies (DEEs) comprise a diverse range of disorders that can arise from both genetic and non-genetic causes. Genetic DEEs are linked to pathogenic variants in various genes with different molecular functions. The wide clinical and genetic variability found in DEEs poses a considerable challenge for accurate diagnosis even with the use of comprehensive diagnostic approaches such as whole genome sequencing (WGS). CASE PRESENTATION:In this study, we describe a girl with a clinical presentation of DEE. Using WGS, we identified several candidate variants in the HNRNPU, NIPBL, and KANSL1 genes with partial overlap with the patient's clinical presentation. Subsequent analysis revealed that only the variant in the HNRNPU gene arose de novo, while the others were inherited from unaffected parents. The variant in HNRNPU was determined to be causative. However, the previously reported pathogenic loss-of-function (LoF) variant in KANSL1, inherited from a healthy mother, complicated the interpretation of the results. A thorough investigation using RNA analysis showed that the variant in the KANSL1 gene is located in a duplicated locus, which does not produce a functional protein, explaining the lack of the variant's contribution to the development of the pathological phenotype. CONCLUSIONS:This case illustrates the importance of integrating WGS with additional analyses to accurately diagnose and understand the molecular basis of the lack of influence of the LoF variant in KANSL1 on the patient's phenotype.

Uniparental disomies (UPDs) are among the causes of imprinting disorders. Specific phenotypes of most causative UPDs have been described. Here, we describe the case of a 2-year-old female patient who presented a syndromic phenotype. Chromosomal microarray analysis revealed UPD of the whole chromosome 16. Microsatellite analysis demonstrated paternal origin of the UPD and its isodisomic pattern (UPiD (16) pat). Mosaic trisomy 16 was not detected using the FISH method. Whole-exome sequencing revealed no pathogenetic genetic variants sufficient to explain the syndromic phenotype nor unmasked pathogenic recessive genetic variants on chromosome 16. Whole-genome trio DNA sequencing revealed no additional candidate pathogenic genetic variants to those detected by whole-exome sequencing, including miRNAs and lncRNAs. Imprinting disorders at 6q24.2, 7p12.2, 7q32.2, 11p15.5, 14q32.2, 15q11.2, and 20q13.32, as well as multilocus imprinting disturbances (MLIDs), were excluded by Methylation-Specific Multiplex Ligation-Dependent Probe Amplification (MS-MLPA). At the same time, we detected abnormal hypermethylation of the ZNF597 transcription start site differentially methylated region (ZNF597:TSS-DMR), accompanied by hypomethylation of the neighbouring ZNF597:3' DMR. Both DMRs were normally imprinted, and the DNA alterations in our patient with UPD (16) pat are opposite to those previously described for maternal uniparental disomy (UPD (16) mat). To date, several cases of UPD (16) pat have been reported. Our case report describes the syndromic phenotype of a patient with paternal uniparental disomy of chromosome 16 in contrast to the previously described patients with a normal phenotype or with abnormal phenotypes caused by acquired homozygosity of pathogenic variants at autosomal recessive genes located on this chromosome. Reporting such observations will help systematize data on the phenotypes of imprinting disorders on chromosome 16.

Background: oculocutaneous albinism (OCA) is a hereditary impairment of skin, hair, and eye pigmentation. The most common form of albinism is autosomal recessive albinism, caused by mutations in the TYR gene, accounting for approximately 40–50% of all cases of the disease in European populations. Common hypomorphic variants in the TYR gene could lead to a mild form of albinism in a compound heterozygous state with a pathogenic variant. Methods: we examined by allele specific MLPA a cohort consisting of 118 unrelated patients with albinism and 10 parents of these patients. The control cohort consisted of 200 unexamined Russian residents. Results: the patients with albinism were divided into three groups: without pathogenic variants in the TYR gene—70 patients, with one pathogenic variant in the TYR gene—20 patients, and with two pathogenic variants in the TYR gene—28 patients. Among the 20 patients with a single heterozygous variant in the TYR gene, 15 patients had the c.575C>A p.(Ser192Tyr) variant, and 15 had the c.1205G>A p.(Arg402Gln) variant. Both the c.575C>A p.(Ser192Tyr) and c.1205G>A p.(Arg402Gln) variants were identified in 12 patients. In addition to the aforementioned variants, an intronic variant c.1185-6208A>G (rs147546939) was identified in seven patients. Conclusions: the frequencies and the number of alleles c.575A, c.1205A, and c.1185-6208G in different groups of patients and the control group were compared. In this study, we demonstrate that the complex alleles [c.575C>A p.(Ser192Tyr); c.1205G>A p.(Arg402Gln)] and [c.575C>A p.(Ser192Tyr); c.1185-6208A>G; c.1205G>A p.(Arg402Gln)] are associated with oculocutaneous albinism, which is consistent with findings from other researchers.

Background Epilepsy is a prevalent neurological disorder, affecting approximately 1% of the global population. The extensive clinical and genetic variability in epilepsy makes accurate diagnosis a significant challenge. Case presentation In this study, we describe a girl with a clinical presentation of developmental and epileptic encephalopathy (DEE). Using whole genome sequencing (WGS), we identified several candidate variants in the HNRNPU, NIPBL, and KANSL1 genes with partial overlap with the patient clinical presentation. Subsequent analysis revealed that only the variant in the HNRNPU gene arose de novo while the others were inherited from an unaffected parents. However, the previously reported pathogenic loss of function variant in the KANSL1 gene, inherited from a healthy mother, complicated comprehensive family counseling. A thorough investigation using RNA analysis showed that the variant in the KANSL1 gene is located in a duplicated locus, which is not functional, explaining the assumed incomplete penetrance. Conclusions This case illustrates the importance of integrating WGS with additional analyses to accurately diagnose and understand the molecular basis of incomplete penetrance in the KANSL1 gene.

Noonan syndrome is a group of diseases with a similar clinical picture, consisting of 16 diseases caused by mutations in 15 genes. According to the literature, approximately half of all cases are attributed to Noonan syndrome type 1, NSML, caused by mutations in the PTPN11 gene. We analyzed 456 unrelated probands using a gene panel NGS, and in 206 cases, the cause of the disease was identified. Approximately half of the cases (107) were caused by variants in the PTPN11 gene, including three previously undescribed variants, one of which was classified as VOUS, and the other two as LP causative complex alleles. Frequent variants of the PTPN11 gene characteristics for Russian patients were identified, accounting for more than 38% (c.922A>G p.Asn308Asp, c.417G>C p.Glu139Asp, c.1403C>T p.Thr468Met) of all cases with mutations in the PTPN11 gene. A comparative characterization of frequent variants of the PTPN11 gene in different populations is shown. The most common features of Noonan syndrome in the studied sample were facial dysmorphisms and cardiovascular system abnormalities. A lower representation of patients with growth delay was observed compared to previously described samples.

Alagille syndrome (ALGS) is a multisystem condition characterized by cholestasis and bile duct paucity on liver biopsy and variable involvement of the heart, skeleton, eyes, kidneys, and face and caused by pathogenic variants in the JAG1 or NOTCH2 gene. The variable expressivity of the clinical phenotype and the lack of genotype-phenotype correlations lead to significant diagnostic difficulties. Here we present an analysis of 18 patients with cholestasis who were diagnosed with ALGS. We used an NGS panel targeting coding exons of 52 genes, including the JAG1 and NOTCH2 genes. Sanger sequencing was used to verify the mutation in the affected individuals and family members. The specific facial phenotype was seen in 16/18 (88.9%). Heart defects were seen in 8/18 (44.4%) patients (pulmonary stenosis in 7/8). Butterfly vertebrae were seen in 5/14 (35.7%) patients. Renal involvement was detected in 2/18 (11.1%) cases-one patient had renal cysts, and one had obstructive hydronephrosis. An ophthalmology examination was performed on 12 children, and only one had posterior embryotoxon (8.3%). A percutaneous liver biopsy was performed in nine cases. Bile duct paucity was detected in six/nine cases (66.7%). Two patients required liver transplantation because of cirrhosis. We identified nine novel variants in the JAG1 gene-eight frameshift variants (c.1619_1622dupGCTA (p.Tyr541X), c.1160delG (p.Gly387fs), c.964dupT (p.C322fs), c.120delG (p.L40fs), c.1984dupG (p.Ala662Glyfs), c.3168_3169delAG (p.R1056Sfs*51), c.2688delG (p.896CysfsTer49), c.164dupG (p.Cys55fs)) and one missense variant, c.2806T > G (p.Cys936Gly). None of the patients presented with NOTCH2 variants. In accordance with the classical criteria, only six patients could meet the diagnostic criteria in our cohort without genetic analysis. Genetic testing is important in the diagnosis of ALGS and can help differentiate it from other types of cholestasis.

A new de novo frameshift variant has been identified in the CASZ1 gene leading to severe dilated cardiomyopathy. Methods: The proband was analyzed with WES NGS, post-mortem, using dried blood spots on filters. The variant was verified with Sanger sequencing for the proband and her parents. Results: We reported a proband with a new de novo frameshift mutation, c.3781del (p.(Trp1261GlyfsTer29)), in the CASZ1 gene. The clinical presentation was similar to the severe phenotype described in previous studies. Conclusions: In this study, we described a new case with a frameshift mutation in CASZ1 causing a severe phenotype of dilated cardiomyopathy.

Hearing loss is one of the most genetically heterogeneous disorders known. Over 120 genes are reportedly associated with non-syndromic hearing loss (NSHL). To date, in Russia, there have been relatively few studies that apply massive parallel sequencing (MPS) methods to elucidate the genetic factors underlying non-GJB2-related hearing loss cases. The current study is intended to provide an understanding of the mutation spectrum in non-GJB2-related hearing loss in a cohort of Russian sensorineural NSHL patients and establish the best diagnostic algorithm. Genetic testing using an MPS panel, which included 33 NSHL and syndromic hearing loss (SHL) genes that might be misdiagnosed as NSHL genes, was completed on 226 sequentially accrued and unrelated patients. As a result, the molecular basis of deafness was found in 21% of the non-GJB2 NSHL cases. The total contribution pathogenic, and likely pathogenic, variants in the genes studied among all hereditary NSHL Russian patients was 12%. STRC pathogenic and likely pathogenic, variants accounted for 30% of diagnoses in GJB2-negative patients, providing the most common diagnosis. The majority of causative mutations in STRC involved large copy number variants (CNVs) (80%). Among the point mutations, the most common were c.11864G>A (p.Trp3955*) in the USH2A gene, c.2171_2174delTTTG (p.Val724Glyfs*6) in the STRC gene, and c.107A>C (p.His36Pro) and c.1001G>T (p.Gly334Val) in the SLC26A4 gene. Pathogenic variants in genes involved in SHL accounted for almost half of the cases with an established molecular genetic diagnosis, which were 10% of the total cohort of patients with non-GJB2-related hearing loss.