Novel SOX10 Mutations in Waardenburg Syndrome: Functional Characterization and Genotype-Phenotype Analysis

A novel frameshift mutation of SOX10 identified in Waardenburg syndrome type 2

Waardenburg syndrome type 2 (WS2) is an autosomal dominant disorder characterized by congenital sensorineural hearing loss, blue iris, and abnormal pigmentation of the hair and skin. WS2 is genetically heterogeneous, often resulting from pathogenic mutations in SOX10 gene. We identified a novel heterozygous frameshift mutation in SOX10 (NM_006941.4: c.22delT, p.S8Rfs*5) in a two-generation Chinese family with WS2 through whole exome sequencing. This mutation was present in both the proband, who exhibited typical features of hearing loss and pigmentation abnormalities, and his father, who showed only mild facial features. Quantitative real-time PCR revealed that the frameshift mutation leads to a reduced expression levels of SOX10 in the peripheral blood of mutation carriers. Our findings expand the spectrum of pathogenic mutations in SOX10 associated with WS2, providing valuable information for prenatal diagnosis and preimplantation screening, and underscore the role of genetic diagnosis in identifying atypical patients.

Chromatin remodeller Chd7 is developmentally regulated in the neural crest by tissue-specific transcription factors

Neurocristopathies such as CHARGE syndrome result from aberrant neural crest development. A large proportion of CHARGE cases are attributed to pathogenic variants in the gene encoding CHD7, chromodomain helicase DNA binding protein 7, which remodels chromatin. While the role for CHD7 in neural crest development is well documented, how this factor is specifically up-regulated in neural crest cells is not understood. Here, we use epigenomic profiling of chick and human neural crest to identify a cohort of enhancers regulating Chd7 expression in neural crest cells and other tissues. We functionally validate upstream transcription factor binding at candidate enhancers, revealing novel epistatic relationships between neural crest master regulators and Chd7, showing tissue-specific regulation of a globally acting chromatin remodeller. Furthermore, we find conserved enhancer features in human embryonic epigenomic data and validate the activity of the human equivalent CHD7 enhancers in the chick embryo. Our findings embed Chd7 in the neural crest gene regulatory network and offer potentially clinically relevant elements for interpreting CHARGE syndrome cases without causative allocation.

Endogenous Sox8 is a critical factor for timely remyelination and oligodendroglial cell repletion in the cuprizone model

Genome-wide association studies identified a single nucleotide polymorphism (SNP) downstream of the transcription factor Sox8, associated with an increased risk of multiple sclerosis (MS). Sox8 is known to influence oligodendrocyte terminal differentiation and is involved in myelin maintenance by mature oligodendrocytes. The possible link of a Sox8 related SNP and MS risk, along with the role of Sox8 in oligodendrocyte physiology prompted us to investigate its relevance during de- and remyelination using the cuprizone model. Sox8-/- mice and wildtype littermates received a cuprizone diet for 5 weeks (wk). Sox8-/- mice showed reduced motor performance and weight compared to wildtype controls. Brains were histologically analysed at the maximum of demyelination (wk 5) and on two time points during remyelination (wk 5.5 and wk 6) for oligodendroglial, astroglial, microglial and myelin markers. We identified reduced proliferation of oligodendrocyte precursor cells at wk 5 as well as reduced numbers of mature oligodendrocytes in Sox8-/- mice at wk 6. Moreover, analysis of myelin markers revealed a delay in remyelination in the Sox8-/- group, demonstrating the potential importance of Sox8 in remyelination processes. Our findings present, for the first time, compelling evidence of a significant role of Sox8 in the context of a disease model.

Case report: Severe nonketotic hyperglycinemia in a neonate without apparent seizures but concomitant cleft palate and cerebral sinovenous thrombosis

Nonketotic hyperglycinemia (NKH) is in most cases a fatal inborn error of metabolism which usually presents during the neonatal period as encephalopathy and refractory seizures. The reported congenital anomalies associated with NKH included corpus callosal agenesis, club foot, cleft palate, and congenital heart disease. Here, we report a newborn who presented with encephalopathy without overt seizures, cerebral venous sinus thrombosis, and cleft palate. Electroencephalography showed a burst suppression pattern, which suggests the etiology could be due to a metabolic or genetic disorder. The amino acid analysis of plasma and cerebrospinal fluid showed elevated glycine. Whole exome sequencing identified a heterozygous c.492C > G; p.Tyr164Ter variant in exon 4 of the GLDC gene inherited from the patient's father. Further long-read whole genome sequencing revealed an exon 1-2 deletion in the GLDC gene inherited from the patient's mother. Additional analyses revealed no pathogenic variants of the cleft palate-related genes. The cleft palate may be an associated congenital anomaly in NKH. Regarding cerebral venous sinus thrombosis, we found a heterozygous variant (p.Arg189Trp) of the PROC gene, which is a common cause of thrombophilia among Thai newborns. A neonate with NKH could present with severe encephalopathy without seizures. A close follow up for clinical changes and further next generation sequencing are crucial for definite diagnosis in neonates with encephalopathy of unclear cause.

[Analysis of molecular genetics and clinical characteristics of 3 children with Waardenburg syndrome]

Objective:To analyze the molecular genetics and clinical characteristics of 3 children with syndromic deafness were analyzed to clarify their causative genes and genetic characteristics. Methods:The medical records of 3 children and their parents were collected and analyzed, including physical examination, hearing evaluation, temporal bone CT, and cranial MRI. Whole-exome sequencing（WES） was used to screen for pathogenic gene variants, and Sanger sequencing was used to verify the candidate positive variants in the probands and their parents. Results:All 3 patients were female with normal intelligence. Patient 1 and 3 had a family history of deafness, which conformed to the pattern of autosomal dominant inheritance. All three patients had bilateral profound sensorineural hearing impairment with bright-blue sclera. Other phenotypes included hypertelorism（patient 1）, multiple dyschromatosis（patient 2）, and yellowish hair（patient 2）, blepharoptosis（patient 3）. Patient 3 had bilateral vestibular enlargement, internal auditory canal enlargement, and bilateral inner ear malformations. Mother of patient 1 had only left mild hearing impairment; mother of patient 3 had bilateral hearing impairment with unilateral bright-blue sclera and yellowish hair. WES detected heterozygous variants, PAX3 c.811C>T, MITF c.632T>C, and SOX10 c.1359_1360 insGCCCCACA, in patient 1, 2, and 3, respectively. The variants in patient 1 and 3 were inherited from their mothers who had hearing impairment, and MITFvariant in patient 2 may be a spontaneous variation. The final diagnoses were that patient 1 with Waardenburg syndrome type 1（WS1）, and the mother of patient 1, patient 2, patient 3, and the mother of patient 3 with WS2. Conclusion:WS is a syndromic deafness, and the main clinical features include autosomal dominant inheritance and scleral pigment abnormalities. However, the findings of this study show that there is still phenotypic heterogeneity in WS even caused by the same gene variant, so it depends on genetic tests to confirm the diagnosis; The gene variant of patient 1 and 2 was never been reported in other patients, which expands the pathogenic variant spectrum of WS.

Tenuous Transcriptional Threshold of Human Sex Determination. I. SRY and Swyer Syndrome at the Edge of Ambiguity

Male sex determination in mammals is initiated by SRY, a Y-encoded transcription factor. The protein contains a high-mobility-group (HMG) box mediating sequence-specific DNA bending. Mutations causing XY gonadal dysgenesis (Swyer syndrome) cluster in the box and ordinarily arise de novo. Rare inherited variants lead to male development in one genetic background (the father) but not another (his sterile XY daughter). De novo and inherited mutations occur at an invariant Tyr adjoining the motif's basic tail (box position 72; Y127 in SRY). In SRY-responsive cell lines CH34 and LNCaP, de novo mutations Y127H and Y127C reduced SRY activity (as assessed by transcriptional activation of principal target gene Sox9) by 5- and 8-fold, respectively. Whereas Y127H impaired testis-specific enhancer assembly, Y127C caused accelerated proteasomal proteolysis; activity was in part rescued by proteasome inhibition. Inherited variant Y127F was better tolerated: its expression was unperturbed, and activity was reduced by only twofold, a threshold similar to other inherited variants. Biochemical studies of wild-type (WT) and variant HMG boxes demonstrated similar specific DNA affinities (within a twofold range), with only subtle differences in sharp DNA bending as probed by permutation gel electrophoresis and fluorescence resonance-energy transfer (FRET); thermodynamic stabilities of the free boxes were essentially identical. Such modest perturbations are within the range of species variation. Whereas our cell-based findings rationalize the de novo genotype-phenotype relationships, a molecular understanding of inherited mutation Y127F remains elusive. Our companion study uncovers cryptic biophysical perturbations suggesting that the para-OH group of Y127 anchors a novel water-mediated DNA clamp.

A novel TCN2 mutation with unusual clinical manifestations of hemolytic crisis and unexplained metabolic acidosis: expanding the genotype and phenotype of transcobalamin II deficiency

Background

Transcobalamin deficiency is a rare inborn metabolic disorder, characterized by pancytopenia, megaloblastic anemia, failure to thrive, diarrhea, and psychomotor retardation.

Case presentation

We describe a patient who first presented at 3 months of age, with pancytopenia, hepatosplenomegaly, recurrent infection, metabolic acidosis, and acute hemolytic crisis. Extensive hematologic and immunologic investigations did not identify inherited bone marrow failure syndrome, acute leukemia or its related disorders. Whole exome sequencing identified a novel homozygous TCN2 mutation, c.428-2A > G and mRNA study confirmed an aberrant transcription of exon 4 skipping. The mutant protein is predicted to have an in-fame 51 amino acids deletion (NP_000346:p.Gly143_Val193del). The patient exhibited marked clinical improvement following hydroxocobalamin treatment.

Conclusions

Transcobalamin deficiency should be investigated in infants with unexplained pancytopenia and acute hemolytic crisis with or without typical evidence of vitamin B12 deficiency.

Three novel variants in SOX10 gene: Waardenburg and PCWH syndromes

Background

Waardenburg syndrome (WS) is a rare genetic disorder characterized by musculoskeletal abnormalities, deafness and hypopigmentation of hair and skin. This article’s aim is to investigate clinical and genetic characteristics of WS in three unrelated Caucasian individuals.

Case presentation

The first patient was a 25-year-old female with congenital bilateral hearing loss, bright-blue-eyes, hypopigmentation of hair and skin, megacolon, language retardation, tenosynovitis and neuromas. The second case was an infant symptomatic from birth, with dysphagia, Hirschsprung disease and neurological abnormalities. The third patient was a 14-year-old boy with congenital bilateral hearing loss and ileocolic Hirschsprung disease. In order to identify variants in potentially causal genes of the patients’ phenotype, genetical testing was conducted: targeted clinical exome, targeted exome and trio exome, respectively. We identified three novel variants spread throughout the coding sequence of SOX10. The c.395C>G variant identified de novo in patient 1 was a single nucleotide substitution in exon 2. The c.850G>T variant identified as heterozygous in patient 2 was a loss-of-function variant that generated a premature stop codon. The c.966dupT variant identified in patient 3 was a duplication that generated a premature stop codon. It had been identified in his father, arising a possible germinal mosaicism. According to in silico predictors the variant identified in patient 1 was considered as pathogenic, whereas the other two were classified as likely pathogenic.

Conclusions

An exact description of the mutations responsible for WS provides useful information to explain clinical features of WS and contributes to better genetic counselling of WS patients.

Bilateral cochlear implantation in a child with Waardenburg syndrome: A case report

BACKGROUND

Waardenburg syndrome (WS) is a rare genetic disorder that presents with clinical characteristics such as white forelock, congenital deafness, dystopia canthorum, and heterochromia iridis. It is mostly transmitted through an autosomal dominant mode, with a few genetic mutations. Children with WS often require surgical intervention at an early age and may have a difficult airway, which can be challenging for anesthesiologists.

CASE PRESENTATION

We report the anesthetic management during cochlear implantation in a 14-month-old girl with WS who weighed 9 kg. In addition to hearing loss and delayed speech, she presented with motor developmental delay, chewing and swallowing impairments, and dietary bucking. Resistance was encountered during tracheal intubation after anesthesia induction, and the tracheal tube was successfully intubated after rotation.

CONCLUSIONS

We report the anesthetic management during cochlear implantation in a child with WS, briefly describe the research advances related to WS, and discuss the optimization of the perioperative management of these children, including airway management, anesthesia-related complications, and the use of anesthetics.

SOX10: 20 years of phenotypic plurality and current understanding of its developmental function

SOX10 belongs to a family of 20 SRY (sex-determining region Y)-related high mobility group box-containing (SOX) proteins, most of which contribute to cell type specification and differentiation of various lineages. The first clue that SOX10 is essential for development, especially in the neural crest, came with the discovery that heterozygous mutations occurring within and around SOX10 cause Waardenburg syndrome type 4. Since then, heterozygous mutations have been reported in Waardenburg syndrome type 2 (Waardenburg syndrome type without Hirschsprung disease), PCWH or PCW (peripheral demyelinating neuropathy, central dysmyelination, Waardenburg syndrome, with or without Hirschsprung disease), intestinal manifestations beyond Hirschsprung (ie, chronic intestinal pseudo-obstruction), Kallmann syndrome and cancer. All of these diseases are consistent with the regulatory role of SOX10 in various neural crest derivatives (melanocytes, the enteric nervous system, Schwann cells and olfactory ensheathing cells) and extraneural crest tissues (inner ear, oligodendrocytes). The recent evolution of medical practice in constitutional genetics has led to the identification of SOX10 variants in atypical contexts, such as isolated hearing loss or neurodevelopmental disorders, making them more difficult to classify in the absence of both a typical phenotype and specific expertise. Here, we report novel mutations and review those that have already been published and their functional consequences, along with current understanding of SOX10 function in the affected cell types identified through in vivo and in vitro models. We also discuss research options to increase our understanding of the origin of the observed phenotypic variability and improve the diagnosis and medical care of affected patients.

Molecular and genetic characterization of a large Brazilian cohort presenting hearing loss

Hearing loss is one of the most common sensory defects, affecting 5.5% of the worldwide population and significantly impacting health and social life. It is mainly attributed to genetic causes, but their relative contribution reflects the geographical region's socio-economic development. Extreme genetic heterogeneity with hundreds of deafness genes involved poses challenges for molecular diagnosis. Here we report the investigation of 542 hearing-impaired subjects from all Brazilian regions to search for genetic causes. Biallelic GJB2/GJB6 causative variants were identified in 12.9% (the lowest frequency was found in the Northern region, 7.7%), 0.4% carried GJB2 dominant variants, and 0.6% had the m.1555A > G variant (one aminoglycoside-related). In addition, other genetic screenings, employed in selected probands according to clinical presentation and presumptive inheritance patterns, identified causative variants in 2.4%. Ear malformations and auditory neuropathy were diagnosed in 10.8% and 3.5% of probands, respectively. In 3.8% of prelingual/perilingual cases, Waardenburg syndrome was clinically diagnosed, and in 71.4%, these diagnoses were confirmed with pathogenic variants revealed; seven out of them were novel, including one CNV. All these genetic screening strategies revealed causative variants in 16.2% of the cases. Based on causative variants in the molecular diagnosis and genealogy analyses, a probable genetic etiology was found in ~ 50% of the cases. The present study highlights the relevance of GJB2/GJB6 as a cause of hearing loss in all Brazilian regions and the importance of screening unselected samples for estimating frequencies. Moreover, when a comprehensive screening is not available, molecular diagnosis can be enhanced by selecting probands for specific screenings.

A Novel Homozygous PKP2 Variant in Severe Neonatal Non-compaction and Concomitant Ventricular Septal Defect: A Case Report

Left ventricular non-compaction (LVNC) is a rare and genetically heterogeneous cardiomyopathy. The disorder vastly affects infants and young children. Severe neonatal LVNC is relatively rare. The prevalence of genetic defects underlying pediatric and adult-onset LVNC is about 17-40%. Mutations of MYH7 and MYBPC3 sarcomeric genes are found in the vast majority of the positive pediatric cases. PKP2 encodes plakophilin-2, a non-sarcomeric desmosomal protein, which has multiple roles in cardiac myocytes including cell-cell adhesion, tightening gap junction, and transcriptional factor. Most of the reported PKP2 mutations are heterozygous missense and truncating variants, and they are associated with an adult-onset autosomal dominant disorder, namely arrhythmogenic right ventricular dysplasia/cardiomyopathy (ARVD/C). Homozygous PKP2 mutations have been rarely described. Herein, we present a rare case of an infant with neonatal onset of congestive heart failure owing to severe LVNC and multiple muscular VSD. Medical treatments failed to control the heart failure and the patient died at 11 months of age. Whole-exome sequencing identified a novel homozygous PKP2 variant, c.1511-1G>C, in the patient. An mRNA analysis revealed aberrant transcript lacking exon 7, which was predicted to cause a frameshift and truncated peptide (p.Gly460GlufsTer2). The heterozygous parents had normal cardiac structures and functions as demonstrated by electrocardiogram and echocardiography. Pathogenic variants of sarcomeric genes analyzed were not found in the patient. We conducted a literature review and identified eight families with biallelic PKP2 mutations. We observed that three families (our included) with null variants were linked to lethal phenotypes, while homozygous missense mutations resulted in less severe manifestations: adolescent-onset ARVD/C and childhood-onset DCM. Our data support a previous notion that severe neonatal LVNC might represent a unique entity and had distinct genetic spectrum. In conclusion, the present study has extended the phenotypes and genotypes of PKP2-related disorders and lethal LVNC.