Usher syndrome: molecular links of pathogenesis, proteins and pathways

In vivoand dosimetric investigation on electrical vestibular stimulation with frequency- and amplitude-modulated currents

Objective. Normal function of the vestibular system can be disturbed using a noninvasive technique called electrical vestibular stimulation (EVS), which alters a person's sense of balance and causes false sensations of movement. EVS has been widely used to study the function of the vestibular system, and it has recently gained interest as a therapeutic tool to improve postural stability and help those suffering from vestibular dysfunction. Yet, understanding of how EVS stimulates the vestibular system, the current intensity needed to produce an effect and the frequencies at which it occurs have remained unclear.Approach. The effect of EVS on postural sway was examined in five participants using sinusoidal alternating current with time-varying amplitude from 0 to 1.5 mA and frequency from 0.1 to 10 Hz for three electrode configurations. Dosimetry of the current flow inside the head was conducted using anatomically realistic computational models created individually for each subject based on magnetic resonance imaging data. An estimate for the minimal field strength capable of affecting the vestibular system was calculated with the finite element method.Main results. Bipolar EVS at frequencies up to 10 Hz caused harmonic full-body swaying, and the frequency of the sway was the same as that of the stimulation current. The size of the sway was amplified by increasing the current intensity. Dosimetry modeling indicated that, for 0.2 mA current, the average electric field strength in the vestibular system was approximately 10-30 mV m-1, depending on the electrode montage. The size of the measured postural sway was proportional to the montage-specific electric field strength in the vestibular system.Significance. The results provide insight to EVS's working mechanisms and improve its potential as a tool to study the sense of balance.

Epithelial UNC-23 limits mechanical stress to maintain glia-neuron architecture in C. elegans

For an organ to maintain correct architecture and function, its diverse cellular components must coordinate their size and shape. Although cell-intrinsic mechanisms driving homotypic cell-cell coordination are known, it is unclear how cell shape is regulated across heterotypic cells. We find that epithelial cells maintain the shape of neighboring sense-organ glia-neuron units in adult Caenorhabditis elegans (C. elegans). Hsp co-chaperone UNC-23/BAG2 prevents epithelial cell shape from deforming, and its loss causes head epithelia to stretch aberrantly during animal movement. In the sense-organ glia, amphid sheath (AMsh), this causes progressive fibroblast growth factor receptor (FGFR)-dependent disruption of the glial apical cytoskeleton. Resultant glial cell shape alteration causes concomitant shape change in glia-associated neuron endings. Epithelial UNC-23 maintenance of glia-neuron shape is specific both spatially, within a defined anatomical zone, and temporally, in a developmentally critical period. As all molecular components uncovered are broadly conserved across central and peripheral nervous systems, we posit that epithelia may similarly regulate glia-neuron architecture cross-species.

Clinical characterizations and molecular genetic study of two co-segregating variants in PDZD7 and PDE6C genes leading simultaneously to non-syndromic hearing loss and achromatopsia

BACKGROUND

Autosomal recessive non-syndromic hearing loss (NSHL) and cone dystrophies (CODs) are highly genetically and phenotypically heterogeneous disorders. In this study, we applied the whole exome sequencing (WES) to find the cause of HL and COD in an Iranian consanguineous family with three affected individuals.

METHODS

Three members from an Iranian consanguineous family who were suffering from NSHL and visual impairment were ascertained in this study. Comprehensive clinical evaluations and genetic analysis followed by bioinformatic and co-segregation studies were performed to diagnose the cause of these phenotypes. Data were collected from 2020 to 2022.

RESULTS

All cases showed congenital bilateral NSHL, decreased visual acuity, poor color discrimination, photophobia and macular atrophy. Moreover, cornea, iris and anterior vitreous were within normal limit in both eyes, decreased foveal sensitivity, central scotoma and generalized depression of visual field were seen in three cases. WES results showed two variants, a novel null variant (p.Trp548Ter) in the PDE6C gene causing COD type 4 (Achromatopsia) and a previously reported variant (p.Ile84Thr) in the PDZD7 gene causing NSHL. Both variants were found in the cis configuration on chromosome 10 with a genetic distance of about 8.3 cM, leading to their co-inheritance. However, two diseases could appear independently in subsequent generations due to crossover during meiosis.

CONCLUSIONS

Here, we could successfully determine the etiology of a seemingly complex phenotype in two adjacent genes. We identified a novel variant in the PDE6C gene, related to achromatopsia. Interestingly, this variant could cooperatively cause visual disorders: cone dystrophy and cone-rod dystrophy.

Multicentric Longitudinal Prospective Study in a European Cohort of MYO7A Patients: Disease Course and Implications for Gene Therapy

Purpose

We investigated the natural history of retinal dystrophy owing to variants in the MYO7A gene.

Methods

Fifty-three patients (mean age, 33.6 ± 16.7 years) with Usher syndrome owing to biallelic, mostly pathogenic, variants in MYO7A underwent baseline and two annual follow-up visits. Best-corrected visual acuity (BCVA), semiautomatic kinetic visual field, full-field electroretinogram, color fundus imaging, microperimetry, spectral-domain optical coherence tomography, and fundus autofluorescence were assessed.

Results

At baseline, all patients presented with decreased BCVA (66.4 ± 17.9 Early Treatment Diabetic Retinopathy score and 59.5 ± 21.7 Early Treatment Diabetic Retinopathy score, in the better- and worse-seeing eyes, respectively), restricted semiautomatic kinetic visual field (III4e area, 3365.8 ± 4142.1°2; 4176.4 ± 4400.3°2) and decreased macular sensitivity (9.7 ± 9.9 dB; 9.0 ± 10.2 dB). Spectral-domain optical coherence tomography revealed reduced central macular thickness (259.6 ± 63.0 µm; 250.7 ± 63.3 µm) and narrowed ellipsoid zone band width (2807.5 ± 2374.6 µm; 2615.5 ± 2370.4 µm). Longitudinal analyses (50 patients) showed a significant decrease of BCVA in better-seeing eyes, whereas no changes were observed in worse-seeing eyes for any parameter. BCVA, semiautomatic kinetic visual field (III4e and V4e) and macular sensitivity were related significantly to age at baseline. Hyperautofluorescent foveal patch (16 eyes [31.4%]) and abnormal central hypoautofluorescence (9 eyes [17.6%]) were significantly associated with worse morphological and functional read-outs compared with the hyperautofluorescent ring pattern (22 eyes [43.1%]).

Conclusions

Our European multicentric study offers the first prospective longitudinal analysis in one of the largest cohorts of MYO7A patients described to date, confirming the slow disease progression. More important, this study emphasizes the key role of fundus autofluorescence patterns in retinal impairment staging and advocates its adoption as an objective biomarker in patient selection for future gene therapy clinical trials.

Carriers of autosomal recessive conditions: are they really 'unaffected?'

Mendel's Law of Dominance suggests that recessive disease expression requires the inheritance of two mutated alleles as the dominant, wildtype allele suppresses disease presentation leading to the expression of physiological normal phenotypes. However, there is existing evidence that challenges this school of thought. Here, we summarise existing literature evaluating metabolic and health impacts among carriers of autosomal recessive conditions, focusing on phenylketonuria (PKU), classical homocystinuria, galactosemia and Usher syndrome as examples. Our findings suggest that carriers, often described as 'unaffected', may actually display attenuated symptoms for the recessive disease they are carrying. For instance, PKU is an inborn error of metabolism characterised by the build-up of plasma phenylalanine attributed to the deficiency of the phenylalanine hydroxylase (PAH) enzyme. While less severe, PKU carriers also exhibit this impaired enzymatic activity, leading to elevated plasma phenylalanine levels, especially after phenylalanine consumption. Related to these metabolic alterations in the PAH pathway, there is early evidence to suggest that PKU carriers may have compromised cognitive and mental health outcomes. Overall, research on the health and metabolic impacts of PKU carriers is sparse, with most studies conducted several decades ago. However, early evidence suggests that intermediate phenotypes among carriers of autosomal recessive conditions are plausible. The illustrated possible intermediate phenotypes observed among carriers necessitates future research to determine possible clinical implications among this population.

Losing, preserving, and restoring vision from neurodegeneration in the eye

The retina is a part of the brain that sits at the back of the eye, looking out onto the world. The first neurons of the retina are the rod and cone photoreceptors, which convert changes in photon flux into electrical signals that are the basis of vision. Rods and cones are frequent targets of heritable neurodegenerative diseases that cause visual impairment, including blindness, in millions of people worldwide. This review summarizes the diverse genetic causes of inherited retinal degenerations (IRDs) and their convergence onto common pathogenic mechanisms of vision loss. Currently, there are few effective treatments for IRDs, but recent advances in disparate areas of biology and technology (e.g., genome editing, viral engineering, 3D organoids, optogenetics, semiconductor arrays) discussed here enable promising efforts to preserve and restore vision in IRD patients with implications for neurodegeneration in less approachable brain areas.

Combined Presence in Heterozygosis of Two Variant Usher Syndrome Genes in Two Siblings Affected by Isolated Profound Age-Related Hearing Loss

Sensorineural age-related hearing loss affects a large proportion of the elderly population, and has both environmental and genetic causes. Notwithstanding increasing interest in this debilitating condition, the genetic risk factors remain largely unknown. Here, we report the case of two sisters affected by isolated profound sensorineural hearing loss after the age of seventy. Genomic DNA sequencing revealed that the siblings shared two monoallelic variants in two genes linked to Usher Syndrome (USH genes), a recessive disorder of the ear and the retina: a rare pathogenic truncating variant in USH1G and a previously unreported missense variant in ADGRV1. Structure predictions suggest a negative effect on protein stability of the latter variant, allowing its classification as likely pathogenic according to American College of Medical Genetics criteria. Thus, the presence in heterozygosis of two recessive alleles, which each cause syndromic deafness, may underlie digenic inheritance of the age-related non-syndromic hearing loss of the siblings, a hypothesis that is strengthened by the knowledge that the two genes are integrated in the same functional network, which underlies stereocilium development and organization. These results enlarge the spectrum and complexity of the phenotypic consequences of USH gene mutations beyond the simple Mendelian inheritance of classical Usher syndrome.

Expression of the human usherin c.2299delG mutation leads to early-onset auditory loss and stereocilia disorganization

Usher syndrome (USH) is the leading cause of combined deafness and blindness, with USH2A being the most prevalent form. The mechanisms responsible for this debilitating sensory impairment remain unclear. This study focuses on characterizing the auditory phenotype in a mouse model expressing the c.2290delG mutation in usherin equivalent to human frameshift mutation c.2299delG. Previously we described how this model reproduces patient's retinal phenotypes. Here, we present the cochlear phenotype, showing that the mutant usherin, is expressed during early postnatal stages. The c.2290delG mutation results in a truncated protein that is mislocalized within the cell body of the hair cells. The knock-in model also exhibits congenital hearing loss that remains consistent throughout the animal's lifespan. Structurally, the stereocilia bundles, particularly in regions associated with functional hearing loss, are disorganized. Our findings shed light on the role of usherin in maintaining structural support, specifically in longer inner hair cell stereocilia, during development, which is crucial for proper bundle organization and hair cell function. Overall, we present a genetic mouse model with cochlear defects associated with the c.2290delG mutation, providing insights into the etiology of hearing loss and offering potential avenues for the development of effective therapeutic treatments for USH2A patients.

Usher Syndrome on the Island of Ireland: A Genotype-Phenotype Review

Purpose

Usher syndrome (USH) is a genetically heterogeneous group of autosomal recessive (AR) syndromic inherited retinal degenerations (IRDs) representing 50% of deaf-blindness. All subtypes include retinitis pigmentosa, sensorineural hearing loss, and vestibular abnormalities. Thorough phenotyping may facilitate genetic diagnosis and intervention. Here we report the clinical/genetic features of an Irish USH cohort.

Methods

USH patients were selected from the Irish IRD registry (Target 5000). Patients were examined clinically (deep-phenotyping) and genetically using a 254 IRD-associated gene target capture sequencing panel, USH2A exon, and whole genome sequencing.

Results

The study identified 145 patients (24.1% USH1 [n = 35], 73.8% USH2 [n = 107], 1.4% USH3 [n = 2], and 0.7% USH4 [n = 1]). A genetic diagnosis was reached in 82.1%, the majority (80.7%) being MYO7A or USH2A genotypes. Mean visual acuity and visual field (VF) were 0.47 ± 0.58 LogMAR and 31.3° ± 32.8°, respectively, at a mean age of 43 years. Legal blindness criteria were met in 40.7%. Cataract was present in 77.4%. ADGRV1 genotypes had the most VF loss, whereas USH2A patients had greater myopia and CDH23 had the most astigmatism. Variants absent from gnomAD non-Finnish Europeans and ClinVar represented more than 20% of the variants identified and were detected in ADGRV1, ARSG, CDH23, MYO7A, and USH2A.

Conclusions

USH is a genetically diverse group of AR IRDs that have a profound impact on affected individuals and their families. The prevalence and phenotype/genotype characteristics of USH in Ireland have, as yet, gone unreported. Understanding the genotype of Irish USH patients may guide clinical and genetic characterization facilitating access to existing/novel therapeutics.

Targeted adaptive long-read sequencing for discovery of complex phased variants in inherited retinal disease patients

Inherited retinal degenerations (IRDs) are a heterogeneous group of predominantly monogenic disorders with over 300 causative genes identified. Short-read exome sequencing is commonly used to genotypically diagnose patients with clinical features of IRDs, however, in up to 30% of patients with autosomal recessive IRDs, one or no disease-causing variants are identified. Furthermore, chromosomal maps cannot be reconstructed for allelic variant discovery with short-reads. Long-read genome sequencing can provide complete coverage of disease loci and a targeted approach can focus sequencing bandwidth to a genomic region of interest to provide increased depth and haplotype reconstruction to uncover cases of missing heritability. We demonstrate that targeted adaptive long-read sequencing on the Oxford Nanopore Technologies (ONT) platform of the USH2A gene from three probands in a family with the most common cause of the syndromic IRD, Usher Syndrome, resulted in greater than 12-fold target gene sequencing enrichment on average. This focused depth of sequencing allowed for haplotype reconstruction and phased variant identification. We further show that variants obtained from the haplotype-aware genotyping pipeline can be heuristically ranked to focus on potential pathogenic candidates without a priori knowledge of the disease-causing variants. Moreover, consideration of the variants unique to targeted long-read sequencing that are not covered by short-read technology demonstrated higher precision and F1 scores for variant discovery by long-read sequencing. This work establishes that targeted adaptive long-read sequencing can generate targeted, chromosome-phased data sets for identification of coding and non-coding disease-causing alleles in IRDs and can be applicable to other Mendelian diseases.

The applications of CRISPR/Cas-mediated genome editing in genetic hearing loss

Hearing loss (HL) can be caused by a number of different genetic factors. Non-syndromic HL refers that HL occurs as an isolated symptom in an individual, whereas syndromic HL refers that HL is associated with other symptoms or abnormalities. To date, more than 140 genes have been identified as being associated with non-syndromic HL, and approximately 400 genetic syndromes can include HL as one of the clinical symptoms. However, no gene therapeutic approaches are currently available to restore or improve hearing. Therefore, there is an urgent necessity to elucidate the possible pathogenesis of specific mutations in HL-associated genes and to investigate the promising therapeutic strategies for genetic HL. The development of the CRISPR/Cas system has revolutionized the field of genome engineering, which has become an efficacious and cost-effective tool to foster genetic HL research. Moreover, several in vivo studies have demonstrated the therapeutic efficacy of the CRISPR/Cas-mediated treatments for specific genetic HL. In this review, we briefly introduce the progress in CRISPR/Cas technique as well as the understanding of genetic HL, and then we detail the recent achievements of CRISPR/Cas technique in disease modeling and therapeutic strategies for genetic HL. Furthermore, we discuss the challenges for the application of CRISPR/Cas technique in future clinical treatments.

The association of genetic polymorphisms in protocadherin 15 with sudden sensorineural hearing loss in a Chinese population

BACKGROUND

Sudden sensorineural hearing loss (SSNHL) is a multifactorial disease, and its etiology is still unknown. SSNHL may be caused by environmental factors and genetic changes. PCDH15 is associated with susceptibility to hearing loss. The relationship between PCDH15 and SSNHL remains unknown.

METHODS

In this study, the potential association between PCDH15 polymorphism and SSNHL in Chinese population was evaluated. Two single nucleotide polymorphisms PCDH15-rs7095441 and rs11004085 in 195 SSNHL patients and 182 healthy controls were determined by TaqMan technology.

RESULTS

In Chinese population, the TT genotype and T allele of rs7095441 are associated with increased susceptibility to SSNHL. The relationships between rs7095441 and the degree of hearing loss were analyzed, and TT genotype increased the risk of hearing loss. Among SSNHL patients, patients with TT genotype of rs7095441 have an increased risk of vertigo.

CONCLUSION

This study found that the TT genotype of SNP rs7095441 can increase the risk of SSNHL in Chinese population.

Expression and subcellular localization of USH1C/harmonin in human retina provides insights into pathomechanisms and therapy

Usher syndrome (USH) is the most common form of hereditary deaf-blindness in humans. USH is a complex genetic disorder, assigned to three clinical subtypes differing in onset, course and severity, with USH1 being the most severe. Rodent USH1 models do not reflect the ocular phenotype observed in human patients to date; hence, little is known about the pathophysiology of USH1 in the human eye. One of the USH1 genes, USH1C, exhibits extensive alternative splicing and encodes numerous harmonin protein isoforms that function as scaffolds for organizing the USH interactome. RNA-seq analysis of human retinae uncovered harmonin_a1 as the most abundant transcript of USH1C. Bulk RNA-seq analysis and immunoblotting showed abundant expression of harmonin in Müller glia cells (MGCs) and retinal neurons. Furthermore, harmonin was localized in the terminal endfeet and apical microvilli of MGCs, presynaptic region (pedicle) of cones and outer segments (OS) of rods as well as at adhesive junctions between MGCs and photoreceptor cells (PRCs) in the outer limiting membrane (OLM). Our data provide evidence for the interaction of harmonin with OLM molecules in PRCs and MGCs and rhodopsin in PRCs. Subcellular expression and colocalization of harmonin correlate with the clinical phenotype observed in USH1C patients. We also demonstrate that primary cilia defects in USH1C patient-derived fibroblasts could be reverted by the delivery of harmonin_a1 transcript isoform. Our studies thus provide novel insights into PRC cell biology, USH1C pathophysiology and development of gene therapy treatment(s).

Potential therapeutic strategies for photoreceptor degeneration: the path to restore vision

Photoreceptors (PRs), as the most abundant and light-sensing cells of the neuroretina, are responsible for converting light into electrical signals that can be interpreted by the brain. PR degeneration, including morphological and functional impairment of these cells, causes significant diminution of the retina's ability to detect light, with consequent loss of vision. Recent findings in ocular regenerative medicine have opened promising avenues to apply neuroprotective therapy, gene therapy, cell replacement therapy, and visual prostheses to the challenge of restoring vision. However, successful visual restoration in the clinical setting requires application of these therapeutic approaches at the appropriate stage of the retinal degeneration. In this review, firstly, we discuss the mechanisms of PR degeneration by focusing on the molecular mechanisms underlying cell death. Subsequently, innovations, recent developments, and promising treatments based on the stage of disorder progression are further explored. Then, the challenges to be addressed before implementation of these therapies in clinical practice are considered. Finally, potential solutions to overcome the current limitations of this growing research area are suggested. Overall, the majority of current treatment modalities are still at an early stage of development and require extensive additional studies, both pre-clinical and clinical, before full restoration of visual function in PR degeneration diseases can be realized.

Affinity purification of in vivo assembled whirlin-associated protein complexes from the zebrafish retina

Mutations in WHRN lead to Usher syndrome type 2d or to non-syndromic hearing impairment. The WHRN-encoded gene product whirlin directly interacts with the intracellular regions of the other two Usher syndrome type 2-associated proteins, usherin and ADGRV1. In photoreceptor cells, this protein complex constitutes fibrous links between the periciliary membrane and the connecting cilium. However, the molecular mechanism(s) of retinal degeneration due to compromised formation and function of the USH2-associated protein complex remains elusive. To unravel this pathogenic mechanism, we isolated and characterized whirlin-associated protein complexes from zebrafish photoreceptor cells. We generated transgenic zebrafish that express Strep/FLAG-tagged Whrna, a zebrafish ortholog of human whirlin, under the control of a photoreceptor-specific promoter. Affinity purification of Strep/FLAG-tagged Whrna and associated proteins from adult transgenic zebrafish retinas followed by mass spectrometry identified 19 novel candidate associated proteins. Pull down experiments and dedicated yeast two-hybrid assays confirmed the association of Whrna with 7 of the co-purified proteins. Several of the co-purified proteins are part of the synaptic proteome, which indicates a role for whirlin in the photoreceptor synapse. Future studies will elucidate which of the newly identified protein-protein interactions contribute to the development of the retinal phenotype observed in USH2d patients. SIGNIFICANCE: Since protein-protein interactions identified using targeted in vitro studies do not always recapitulate interactions that are functionally relevant in vivo, we established a transgenic zebrafish line that stably expresses a Strep/FLAG-tagged ortholog of human whirlin (SF-Whrna) in photoreceptor cells. Affinity purification of in vivo-assembled SF-Whrna-associated protein complexes from retinal lysates followed by mass spectrometry, identified 19 novel candidate interaction partners, many of which are enriched in the synaptic proteome. Two human orthologs of the identified candidate interaction partners, FRMPD4 and Kir2.3, were validated as direct interaction partners of human whirlin using a yeast two-hybrid assay. The strong connection of whirlin with postsynaptic density proteins was not identified in previous in vitro protein-protein interaction assays, presumably due to the absence of a biologically relevant context. Isolation and identification of in vivo-assembled whirlin-associated protein complexes from the tissue of interest is therefore a powerful methodology to obtain novel insight into tissue specific protein-protein interactions and has the potential to improve significantly our understanding of the function of whirlin and the molecular pathogenesis underlying Usher syndrome type 2.

CRISPR/Cas9 editing of the MYO7A gene in rhesus macaque embryos to generate a primate model of Usher syndrome type 1B

Mutations in the MYO7A gene lead to Usher syndrome type 1B (USH1B), a disease characterized by congenital deafness, vision loss, and balance impairment. To create a nonhuman primate (NHP) USH1B model, CRISPR/Cas9 was used to disrupt MYO7A in rhesus macaque zygotes. The targeting efficiency of Cas9 mRNA and hybridized crRNA-tracrRNA (hyb-gRNA) was compared to Cas9 nuclease (Nuc) protein and synthetic single guide (sg)RNAs. Nuc/sgRNA injection led to higher editing efficiencies relative to mRNA/hyb-gRNAs. Mutations were assessed by preimplantation genetic testing (PGT) and those with the desired mutations were transferred into surrogates. A pregnancy was established from an embryo where 92.1% of the PGT sequencing reads possessed a single G insertion that leads to a premature stop codon. Analysis of single peripheral blood leukocytes from the infant revealed that half the cells possessed the homozygous single base insertion and the remaining cells had the wild-type MYO7A sequence. The infant showed sensitive auditory thresholds beginning at 3 months. Although further optimization is needed, our studies demonstrate that it is feasible to use CRISPR technologies for creating NHP models of human diseases.

The genetic and phenotypic landscapes of Usher syndrome: from disease mechanisms to a new classification

Usher syndrome (USH) is the most common cause of deaf–blindness in humans, with a prevalence of about 1/10,000 (~ 400,000 people worldwide). Cochlear implants are currently used to reduce the burden of hearing loss in severe-to-profoundly deaf patients, but many promising treatments including gene, cell, and drug therapies to restore the native function of the inner ear and retinal sensory cells are under investigation. The traditional clinical classification of Usher syndrome defines three major subtypes—USH1, 2 and 3—according to hearing loss severity and onset, the presence or absence of vestibular dysfunction, and age at onset of retinitis pigmentosa. Pathogenic variants of nine USH genes have been initially reported: MYO7A, USH1C, PCDH15, CDH23, and USH1G for USH1, USH2A, ADGRV1, and WHRN for USH2, and CLRN1 for USH3. Based on the co-occurrence of hearing and vision deficits, the list of USH genes has been extended to few other genes, but with limited supporting information. A consensus on combined criteria for Usher syndrome is crucial for the development of accurate diagnosis and to improve patient management. In recent years, a wealth of information has been obtained concerning the properties of the Usher proteins, related molecular networks, potential genotype–phenotype correlations, and the pathogenic mechanisms underlying the impairment or loss of hearing, balance and vision. The advent of precision medicine calls for a clear and more precise diagnosis of Usher syndrome, exploiting all the existing data to develop a combined clinical/genetic/network/functional classification for Usher syndrome.

Deficiency in Retinal TGFβ Signaling Aggravates Neurodegeneration by Modulating Pro-Apoptotic and MAP Kinase Pathways

Transforming growth factor β (TGFβ) signaling has manifold functions such as regulation of cell growth, differentiation, migration, and apoptosis. Moreover, there is increasing evidence that it also acts in a neuroprotective manner. We recently showed that TGFβ receptor type 2 (Tgfbr2) is upregulated in retinal neurons and Müller cells during retinal degeneration. In this study we investigated if this upregulation of TGFβ signaling would have functional consequences in protecting retinal neurons. To this end, we analyzed the impact of TGFβ signaling on photoreceptor viability using mice with cell type-specific deletion of Tgfbr2 in retinal neurons and Müller cells (Tgfbr2^ΔOC) in combination with a genetic model of photoreceptor degeneration (VPP). We examined retinal morphology and the degree of photoreceptor degeneration, as well as alterations of the retinal transcriptome. In summary, retinal morphology was not altered due to TGFβ signaling deficiency. In contrast, VPP-induced photoreceptor degeneration was drastically exacerbated in double mutant mice (Tgfbr2^ΔOC; VPP) by induction of pro-apoptotic genes and dysregulation of the MAP kinase pathway. Therefore, TGFβ signaling in retinal neurons and Müller cells exhibits a neuroprotective effect and might pose promising therapeutic options to attenuate photoreceptor degeneration in humans.

Delivery Strategies for CRISPR/Cas Genome editing tool for Retinal Dystrophies: challenges and opportunities

CRISPR/Cas, an adaptive immune system in bacteria, has been adopted as an efficient and precise tool for site-specific gene editing with potential therapeutic opportunities. It has been explored for a variety of applications, including gene modulation, epigenome editing, diagnosis, mRNA editing, etc. It has found applications in retinal dystrophic conditions including progressive cone and cone-rod dystrophies, congenital stationary night blindness, X-linked juvenile retinoschisis, retinitis pigmentosa, age-related macular degeneration, leber's congenital amaurosis, etc. Most of the therapies for retinal dystrophic conditions work by regressing symptoms instead of reversing the gene mutations. CRISPR/Cas9 through indel could impart beneficial effects in the reversal of gene mutations in dystrophic conditions. Recent research has also consolidated on the approaches of using CRISPR systems for retinal dystrophies but their delivery to the posterior part of the eye is a major concern due to high molecular weight, negative charge, and in vivo stability of CRISPR components. Recently, non-viral vectors have gained interest due to their potential in tissue-specific nucleic acid (miRNA/siRNA/CRISPR) delivery. This review highlights the opportunities of retinal dystrophies management using CRISPR/Cas nanomedicine.

[Hearing loss due to mutations in the genes responsible for Usher syndrome]

Usher syndrome is characterized by congenital bilateral sensorineural hearing loss and progressive retinitis pigmentosa, and has an autosomal recessive type of inheritance. The purpose of this work is to summarize the modern data of a clinical picture of Usher syndrome and analyse hearing impairment properties. The frequency of the syndrome among children suffering from hearing loss and deafness is from 3 to 10%. The prevalence of the syndrome in the world is estimated as 4.4 per 100.000 population. The complexity of the diagnosis of the syndrome lies in the significant clinical and genetic heterogeneity. Hearing and vision problems begin at different ages. Primary diagnosis begins with the clinical diagnosis of bilateral hearing loss and visual impairment manifests later. In this case the initial diagnosis of nonsyndromal hearing loss will not be definitive. Molecular genetic studies contribute to the early clinical diagnosis of the syndrome. Understanding the cause of the disease allows to conduct correct medical and genetic counseling and get closer to solving treatment problems.

Protein Kinase A in Human Retina: Differential Localization of Cβ, Cα, RIIα, and RIIβ in Photoreceptors Highlights Non-redundancy of Protein Kinase A Subunits

Protein kinase A (PKA) signaling is essential for numerous processes but the subcellular localization of specific PKA regulatory (R) and catalytic (C) subunits has yet to be explored comprehensively. Additionally, the localization of the Cβ subunit has never been spatially mapped in any tissue even though ∼50% of PKA signaling in neuronal tissues is thought to be mediated by Cβ. Here we used human retina with its highly specialized neurons as a window into PKA signaling in the brain and characterized localization of PKA Cα, Cβ, RIIα, and RIIβ subunits. We found that each subunit presented a distinct localization pattern. Cα and Cβ were localized in all cell layers (photoreceptors, interneurons, retinal ganglion cells), while RIIα and RIIβ were selectively enriched in photoreceptor cells where both showed distinct patterns of co-localization with Cα but not Cβ. Only Cα was observed in photoreceptor outer segments and at the base of the connecting cilium. Cβ in turn, was highly enriched in mitochondria and was especially prominent in the ellipsoid of cone cells. Further investigation of Cβ using RNA BaseScope technology showed that two Cβ splice variants (Cβ4 and Cβ4ab) likely code for the mitochondrial Cβ proteins. Overall, our data indicates that PKA Cα, Cβ, RIIα, and RIIβ subunits are differentially localized and are likely functionally non-redundant in the human retina. Furthermore, Cβ is potentially important for mitochondrial-associated neurodegenerative diseases previously linked to PKA dysfunction.

Human Radiosensitivity and Radiosusceptibility: What Are the Differences?

The individual response to ionizing radiation (IR) raises a number of medical, scientific, and societal issues. While the term "radiosensitivity" was used by the pioneers at the beginning of the 20st century to describe only the radiation-induced adverse tissue reactions related to cell death, a confusion emerged in the literature from the 1930s, as "radiosensitivity" was indifferently used to describe the toxic, cancerous, or aging effect of IR. In parallel, the predisposition to radiation-induced adverse tissue reactions (radiosensitivity), notably observed after radiotherapy appears to be caused by different mechanisms than those linked to predisposition to radiation-induced cancer (radiosusceptibility). This review aims to document these differences in order to better estimate the different radiation-induced risks. It reveals that there are very few syndromes associated with the loss of biological functions involved directly in DNA damage recognition and repair as their role is absolutely necessary for cell viability. By contrast, some cytoplasmic proteins whose functions are independent of genome surveillance may also act as phosphorylation substrates of the ATM protein to regulate the molecular response to IR. The role of the ATM protein may help classify the genetic syndromes associated with radiosensitivity and/or radiosusceptibility.

USH2A gene variants cause Keratoconus and Usher syndrome phenotypes in Pakistani families

Background

Retinitis pigmentosa (RP) is the most common inherited retinal dystrophy, affecting approximately 1 in 4000 individuals worldwide. The most common form of syndromic RP is Usher syndrome (USH) accounting for approximately 20–30 % of RP cases. Mutations in the USH2A gene cause a significant proportion of recessive non-syndromic RP and USH type II (USH2). This study aimed to determine the causative role of the USH2A gene in autosomal recessive inherited ocular diseases and to establish genotype-phenotype correlation associated with USH2A variants.

Methods

We performed direct Sanger sequencing and co-segregation analysis of the USH2A gene to identify disease causing variants in a non-syndromic RP family, two USH2 families and two Keratoconus (KC) families.

Results

Disease causing variants in the USH2A gene were identified in two families displayed KC and USH2 phenotypes. A novel variant c.4029T > G, p.Asn1343Lys in the USH2A gene was detected in a Pakistani family with KC phenotype. In addition, a missense variant (c.7334 C > T, p. Ser2445Phe) in the USH2A gene was found segregating in another Pakistani family with USH2 phenotype. Homozygosity of identified missense USH2A variants was found associated with autosomal recessive inherited KC and USH2 phenotypes in investigated families. These variants were not detected in ethnically matched healthy controls. Moreover, the USH2A variants were predicted to be deleterious or potentially disease causing by PolyPhen-2, PROVEAN and SIFT.

Conclusions

This study provided first evidence for association of a novel USH2A variant with KC phenotype in a Pakistani family as well as established the phenotype-genotype correlation of a USH2A variant (c.7334 C > T, p. Ser2445Phe) with USH2 phenotype in another Pakistani family. The phenotype-genotype correlations established in present study may improve clinical diagnosis of affected individuals for better management and counseling.

Phylogenetic analysis of Harmonin homology domains

BACKGROUND

Harmonin Homogy Domains (HHD) are recently identified orphan domains of about 70 residues folded in a compact five alpha-helix bundle that proved to be versatile in terms of function, allowing for direct binding to a partner as well as regulating the affinity and specificity of adjacent domains for their own targets. Adding their small size and rather simple fold, HHDs appear as convenient modules to regulate protein-protein interactions in various biological contexts. Surprisingly, only nine HHDs have been detected in six proteins, mainly expressed in sensory neurons.

RESULTS

Here, we built a profile Hidden Markov Model to screen the entire UniProtKB for new HHD-containing proteins. Every hit was manually annotated, using a clustering approach, confirming that only a few proteins contain HHDs. We report the phylogenetic coverage of each protein and build a phylogenetic tree to trace the evolution of HHDs. We suggest that a HHD ancestor is shared with Paired Amphipathic Helices (PAH) domains, a four-helix bundle partially sharing fold and functional properties. We characterized amino-acid sequences of the various HHDs using pairwise BLASTP scoring coupled with community clustering and manually assessed sequence features among each individual family. These sequence features were analyzed using reported structures as well as homology models to highlight structural motifs underlying HHDs fold. We show that functional divergence is carried out by subtle differences in sequences that automatized approaches failed to detect.

CONCLUSIONS

We provide the first HHD databases, including sequences and conservation, phylogenic trees and a list of HHD variants found in the auditory system, which are available for the community. This case study highlights surprising phylogenetic properties found in orphan domains and will assist further studies of HHDs. We unveil the implication of HHDs in their various binding interfaces using conservation across families and a new protein-protein surface predictor. Finally, we discussed the functional consequences of three identified pathogenic HHD variants involved in Hoyeraal-Hreidarsson syndrome and of three newly reported pathogenic variants identified in patients suffering from Usher Syndrome.

Homology modeling and global computational mutagenesis of human myosin VIIa

Usher syndrome type 1B (USH1B) is a genetic disorder caused by mutations in the unconventional Myosin VIIa (MYO7A) protein. USH1B is characterized by hearing loss due to abnormalities in the inner ear and vision loss due to retinitis pigmentosa. Here, we present the model of human MYO7A homodimer, built using homology modeling, and refined using 5 ns molecular dynamics in water. Global computational mutagenesis was applied to evaluate the effect of missense mutations that are critical for maintaining protein structure and stability of MYO7A in inherited eye disease. We found that 43.26% (77 out of 178 in HGMD) and 41.9% (221 out of 528 in ClinVar) of the disease-related missense mutations were associated with higher protein structure destabilizing effects. Overall, most mutations destabilizing the MYO7A protein were found to associate with USH1 and USH1B. Particularly, motor domain and MyTH4 domains were found to be most susceptible to mutations causing the USH1B phenotype. Our work contributes to the understanding of inherited disease from the atomic level of protein structure and analysis of the impact of genetic mutations on protein stability and genotype-to-phenotype relationships in human disease.

Functional Role of Class III Myosins in Hair Cells

Cytoskeletal motors produce force and motion using the energy from ATP hydrolysis and function in a variety of mechanical roles in cells including muscle contraction, cargo transport, and cell division. Actin-based myosin motors have been shown to play crucial roles in the development and function of the stereocilia of auditory and vestibular inner ear hair cells. Hair cells can contain hundreds of stereocilia, which rely on myosin motors to elongate, organize, and stabilize their structure. Mutations in many stereocilia-associated myosins have been shown to cause hearing loss in both humans and animal models suggesting that each myosin isoform has a specific function in these unique parallel actin bundle-based protrusions. Here we review what is known about the classes of myosins that function in the stereocilia, with a special focus on class III myosins that harbor point mutations associated with delayed onset hearing loss. Much has been learned about the role of the two class III myosin isoforms, MYO3A and MYO3B, in maintaining the precise stereocilia lengths required for normal hearing. We propose a model for how class III myosins play a key role in regulating stereocilia lengths and demonstrate how their motor and regulatory properties are particularly well suited for this function. We conclude that ongoing studies on class III myosins and other stereocilia-associated myosins are extremely important and may lead to novel therapeutic strategies for the treatment of hearing loss due to stereocilia degeneration.

Targeted exome sequencing identified a novel USH2A mutation in a Chinese usher syndrome family: a case report

Background

Usher syndrome is a disease with a heterogeneous phenotype and genotype. Our purpose was to identify the gene mutation in a Chinese family with Usher syndrome type 2 and describe the clinical features.

Case presentation

A 23-year-old man complained of a 10-year duration of nyctalopia and a 3-year decline in visual acuity of both eyes accompanied by congenital dysaudia. To clarify the diagnosis, the clinical symptoms were observed and analysed in combination with comprehensive ophthalmologic examinations as well as genetic analysis (targeted exome sequencing, TES). A typical clinical presentation of Usher syndrome of the fundus was found, including a waxy yellow-like disc, bone-spicule formations and retinal vessel stenosis. Optical coherence tomography (OCT) and optical coherence tomography angiography (OCTA) showed loss of the ellipsoid zone and a reduction in paracaval vessel density in both eyes. Genetic analysis identified a novel homozygous c.8483_8486del (p.Ser2828*) mutation in USH2A. The mutation resulted in premature termination of translation and caused the deletion of 19 fibronectin type 3 domains (FN3), transmembrane (TM) region and PDZ-binding motif domain, which play an important role in protein binding. After combining the clinical manifestations and genetic results, the patient was diagnosed with Usher syndrome type 2.

Conclusion

We found a novel c.8483_8486del mutation in the USH2A gene through TES techniques. The results broaden the spectrum of mutations in Usher syndrome type 2 and suggest that a combination of clinical information and molecular diagnosis via TES could help Usher syndrome patients obtain a better diagnosis.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12886-020-01711-7.

Are Consanguineous Marriages to Blame for Usher Syndrome Type 1, a Rare Disease in Pakistan?

Usher syndrome type I is a rare genetic autosomal recessive disease caused by mutations in specific genes that provide instructions for making proteins involved in normal hearing, vision, and balance. It is characterized by hearing impairment due to the inability of auditory nerves to send sensory input to the brain leading to hearing loss along with retinitis pigmentosa (RP), which is a progressive, bilateral, symmetrical retinal degeneration involving photoreceptor cells. We report a 32-year-old male patient who presented to us with complaints of night blindness and progressive vision loss for the past 20 years. He had bilateral hearing loss leading to deaf-mutism. In addition, his developmental milestones were delayed. His fundoscopic findings were consistent with RP and his electroretinography confirmed reduced retinal activity. Pure tone audiometry confirmed bilateral sensory neural hearing. His mother was a known case of Usher syndrome type 1. His family history was remarkable for multiple consanguineous marriages in both his parental and maternal families and a confirmed diagnosis of Usher syndrome in paternal uncle. The patient was tried on hearing aids and vitamin A medication but with minimal improvement in his overall condition. A multidisciplinary approach, involving an audiologist, speech, and language therapist was adapted to help the patient. Early genetic testing can help diagnose such cases in its early stages and genetic counseling regarding the detrimental effects of consanguineous marriages can play a very positive role in genetic diseases, especially those with autosomal recessive inheritance patterns. 

Edge of Scotoma Sensitivity as a Microperimetry Clinical Trial End Point in USH2A Retinopathy

Purpose

Microperimetry is commonly used to assess retinal function. We perform cross-sectional and longitudinal analysis on microperimetry parameters in USH2A retinopathy and explore end points suitable for future clinical trials.

Methods

Microperimetry was performed using two grids, Grid 1 (18° diameter) and Grid 2 (6° diameter). In Grid 1, four parameters (number of nonscotomatous loci, mean sensitivity [MS], responding point sensitivity [RPS], and edge of scotoma sensitivity [ESS]) were analyzed. In Grid 2, number of nonscotomatous loci and MS were examined. Interocular symmetry was also examined. Longitudinal analysis was conducted in a subset of eyes.

Results

Microperimetry could be performed in 16 of 21 patients. In Grid 1 (n = 15; average age, 35.6 years), average number of nonscotomatous loci, MS, RPS, and ESS were 46.6 loci, 10.0 dB, 14.7 and 9.6 dB, respectively. In Grid 2 (n = 13; average age, 37.4 years), 12 eyes had measurable sensitivity across the entire grid. Average MS was 23.8 dB. Interocular analysis revealed large 95% confidence intervals for all parameters. Longitudinally, Grid 1 (n = 12, average follow-up 2.6 years) ESS showed the fastest rate of decline (–1.84 dB/y) compared with MS (–0.34 dB/y) and RPS (–0.90 dB/y).

Conclusions

Our data suggest that ESS may be more useful than MS and RPS in test grids that cover a large extent of the macula. We caution the use of contralateral eye as an internal control.

Translational Relevance

ESS may decrease the duration or sample size of treatment trials in USH2A retinopathy.

Functional, Morphological, and Evolutionary Characterization of Hearing in Subterranean, Eusocial African Mole-Rats

Naked mole-rats are highly vocal, eusocial, subterranean rodents with, counterintuitively, poor hearing. The causes underlying their altered hearing are unknown. Moreover, whether altered hearing is degenerate or adaptive to their unique lifestyles is controversial. We used various methods to identify the factors contributing to altered hearing in naked and the related Damaraland mole-rats and to examine whether these alterations result from relaxed or adaptive selection. Remarkably, we found that cochlear amplification was absent from both species despite normal prestin function in outer hair cells isolated from naked mole-rats. Instead, loss of cochlear amplification appears to result from abnormal hair bundle morphologies observed in both species. By exploiting a well-curated deafness phenotype-genotype database, we identified amino acid substitutions consistent with abnormal hair bundle morphology and reduced hearing sensitivity. Amino acid substitutions were found in unique groups of six hair bundle link proteins. Molecular evolutionary analyses revealed shifts in selection pressure at both the gene and the codon level for five of these six hair bundle link proteins. Substitutions in three of these proteins are associated exclusively with altered hearing. Altogether, our findings identify the likely mechanism of altered hearing in African mole-rats, making them the only identified mammals naturally lacking cochlear amplification. Moreover, our findings suggest that altered hearing in African mole-rats is adaptive, perhaps tailoring hearing to eusocial and subterranean lifestyles. Finally, our work reveals multiple, unique evolutionary trajectories in African mole-rat hearing and establishes species members as naturally occurring disease models to investigate human hearing loss.

Direct Delivery of Antisense Oligonucleotides to the Middle and Inner Ear Improves Hearing and Balance in Usher Mice

Usher syndrome is a syndromic form of hereditary hearing impairment that includes sensorineural hearing loss and delayed-onset retinitis pigmentosa (RP). Type 1 Usher syndrome (USH1) is characterized by congenital profound sensorineural hearing impairment and vestibular areflexia, with adolescent-onset RP. Systemic treatment with antisense oligonucleotides (ASOs) targeting the human USH1C c.216G>A splicing mutation in a knockin mouse model of USH1 restores hearing and balance. Herein, we explore the effect of delivering ASOs locally to the ear to treat hearing and vestibular dysfunction associated with Usher syndrome. Three localized delivery strategies were investigated in USH1C mice: inner ear injection, trans-tympanic membrane injection, and topical tympanic membrane application. We demonstrate, for the first time, that ASOs delivered directly to the ear correct Ush1c expression in inner ear tissue, improve cochlear hair cell transduction currents, restore vestibular afferent irregularity, spontaneous firing rate, and sensitivity to head rotation, and successfully recover hearing thresholds and balance behaviors in USH1C mice. We conclude that local delivery of ASOs to the middle and inner ear reach hair cells and can rescue both hearing and balance. These results also demonstrate the therapeutic potential of ASOs to treat hearing and balance deficits associated with Usher syndrome and other ear diseases.

Structural modeling, mutation analysis, and in vitro expression of usherin, a major protein in inherited retinal degeneration and hearing loss

Usherin is the most common causative protein associated with autosomal recessive retinitis pigmentosa (RP) and Usher syndrome (USH), which are characterized by retinal degeneration alone and in combination with hearing loss, respectively. Usherin is essential for photoreceptor survival and hair cell bundle integrity. However, the molecular mechanism underlying usherin function in normal and disease conditions is unclear. In this study, we investigated structural models of usherin domains and localization of usherin pathogenic small in-frame mutations, mainly homozygous missense mutations. We found that usherin fibronectin III (FN3) domains and most laminin-related domains have a β-sandwich structure. Some FN3 domains are predicted to interact with each other and with laminin-related domains. The usherin protein may bend at some FN3 linker regions. RP- and USH-associated small in-frame mutations are differentially located in usherin domains. Most of them are located at the periphery of β-sandwiches, with some at the interface between interacting domains. The usherin laminin epidermal growth factor repeats adopt a rod-shaped structure, which is maintained by disulfide bonds. Most missense mutations and deletion of exon 13 in this region disrupt the disulfide bonds and may affect local protein folding. Despite low expression of the recombinant entire protein and protein fragments in mammalian cell culture, usherin FN3 fragments are more robustly expressed and secreted than its laminin-related fragments. Our findings provide new insights into the usherin structure and the disease mechanisms caused by pathogenic small in-frame mutations, which will help inform future experimental research on diagnosis, disease mechanisms, and therapeutic approaches.

Atypical and ultra-rare Usher syndrome: a review

Usher syndrome has classically been described as a combination of hearing loss and rod-cone dystrophy; vestibular dysfunction is present in many patients. Three distinct clinical subtypes were documented in the late 1970s. Genotyping efforts have led to the identification of several genes associated with the disease. Recent literature has seen multiple publications referring to "atypical" Usher syndrome presentations. This manuscript reviews the molecular etiology of Usher syndrome, highlighting rare presentations and molecular causes. Reports of "atypical" disease are summarized noting the wide discrepancy in the spectrum of phenotypic deviations from the classical presentation. Guidelines for establishing a clear nomenclature system are suggested.

Mutation screening of the USH2A gene reveals two novel pathogenic variants in Chinese patients causing simplex usher syndrome 2

Background

Usher syndrome (USH) is the most prevalent cause of the human genetic deafness and blindness. USH type II (USH2) is the most common form of USH, and USH2A is the major pathogenic gene for USH2. For expanding the spectrum of USH2A mutations and further revealing the role of USH2A in USH2, we performed the USH2A gene variant screening in Chinese patients with USH2.

Methods

Genomic DNA was extracted from peripheral blood of unrelated Chinese USH2 patients, we designed specific primers for amplifying the coding region (exons 2–72) of the USH2A gene. Sanger sequencing was used to study alleles. Silico prediction tools were used to predict the pathogenicity of the variants identified in these patients.

Results

Five heterozygous pathogenic variants were detected in four patients. Two patients were found to have two-mutations and two patients only have one. Two novel variants c.4217C > A (p.Ser1406X) and c.11780A > G (p.Asp3927Gly)) were predicted deleterious by computer prediction algorithms. In addition, three reported mutations (c.8559-2A > G, c.8232G > C and c.11389 + 3A > T) were also found in this study.

Conclusions

We identified five heterozygous pathogenic variants in the USH2A gene in Chinese patients diagnosed with Usher syndrome type 2, two of which were not reported. It expands the spectrum of USH2A variants in USH.

Genetics of Usher Syndrome: New Insights From a Meta-analysis

OBJECTIVE

To describe the genetic and phenotypic spectrum of Usher syndrome after 6 years of studies by next-generation sequencing, and propose an up-to-date classification of Usher genes in patients with both visual and hearing impairments suggesting Usher syndrome, and in patients with seemingly isolated deafness.

STUDY DESIGN

The systematic review and meta-analysis protocol was based on Cochrane and Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines. We performed 1) a meta-analysis of data from 11 next-generation sequencing studies in 684 patients with Usher syndrome; 2) a meta-analysis of data from 21 next-generation studies in 2,476 patients with seemingly isolated deafness, to assess the involvement of Usher genes in seemingly nonsyndromic hearing loss, and thus the proportion of patients at high risk of subsequent retinitis pigmentosa (RP); 3) a statistical analysis of differences between parts 1) and 2).

RESULTS

In patients with both visual and hearing impairments, the biallelic disease-causing mutation rate was assessed for each Usher gene to propose a classification by frequency: USH2A: 50% (341/684) of patients, MYO7A: 21% (144/684), CDH23: 6% (39/684), ADGRV1: 5% (35/684), PCDH15: 3% (21/684), USH1C: 2% (17/684), CLRN1: 2% (14/684), USH1G: 1% (9/684), WHRN: 0.4% (3/684), PDZD7 0.1% (1/684), CIB2 (0/684). In patients with seemingly isolated sensorineural deafness, 7.5% had disease-causing mutations in Usher genes, and are therefore at high risk of developing RP. These new findings provide evidence that usherome dysfunction is the second cause of genetic sensorineural hearing loss after connexin dysfunction.

CONCLUSION

These results promote generalization of early molecular screening for Usher syndrome in deaf children.

Ocular aspects of Usher syndrome

Introduction: Usher Syndrome is a rare syndrome, which typical expressions are hearing loss, retinitis pigmentosa and in some cases impairment of balance and congenital cataract. It is inherited autosomal recessive. Nine genes whose mutations are associated with this condition have been isolated. It is diagnosed on the basis of clinical and genetic testing. The therapy is aimed at facilitating the functioning of these patients in the environment. Gene therapy is promising in treatment. The purpose of this paper is to focus attention on the specificity and multiplicity of the disease, which would be of educational significance to ophthalmologists and otorhinolaryngologists, through the use of the case report of Usher syndrome. Case report: We present the case of gene confirmed Usher syndrome with 85% hearing loss, retinitis pigmentosa and congenital cataract. Female at the age of 39, pregnant at 26 gestational week, second pregnancy. Genetic investigation by Macedonian Academy of Sciences and Arts (MANU) confirmed double heterozygosity for pathogenic changes c.13010C > T. p. (Thr4337Met) and c.13137delC; p. (Thr4380GinfsTer11) in the USH2A gene, a genotype that confirmed the diagnosis of autosomal recessive disease Usher syndrome type 2A (Usher syndrome 2A). Conclusion: Detailed anamnesis is always required in patients with retinitis pigmentosa, who are referred to an ophthalmologist for hearing and vice versa for patients with hearing loss that are examined by an otorhinolaryngologist. Early diagnosis is important in terms of quality of life, i.e. timely diagnosing and undertaking measures for genetic testing in the family, in order to inform them about the type of the disease and the earlier involvement in educational programs designed for these conditions.

Diseases of the ear

In children with normal hearing, inflammatory disorders caused by infections of the middle ear (otitis media) are the most common ear illnesses. Many of older adults experience some level of hearing loss. Several factors can lead to either a partial loss or the total inability to hear (deafness) including exposure to noise, a hereditary predisposition, chronic infections, traumas, medications, and aging.

Hair-Bundle Links: Genetics as the Gateway to Function

Up to five distinct cell-surface specializations interconnect the stereocilia and the kinocilium of the mature hair bundle in some species: kinocilial links, tip links, top connectors, shaft connectors, and ankle links. In developing hair bundles, transient lateral links are prominent. Mutations in genes encoding proteins associated with these links cause Usher deafness/blindness syndrome or nonsyndromic (isolated) forms of human hereditary deafness, and mice with constitutive or conditional alleles of these genes have provided considerable insight into the molecular composition and function of the different links. We describe the structure of these links and review evidence showing CDH23 and PCDH15 are components of the tip, kinocilial, and transient-lateral links, that stereocilin (STRC) and protein tyrosine phosphatase (PTPRQ) are associated with top and shaft connectors, respectively, and that USH2A and ADGRV1 are associated with the ankle links. Whereas tip links are required for mechanoelectrical transduction, all link proteins play key roles in the normal development and/or the maintenance of hair bundle structure and function. Recent crystallographic and single-particle analyses of PCDH15 and CDH23 provide insight as to how the structure of tip link may contribute to the elastic element predicted to lie in series with the hair cell's mechanoelectrical transducer channel.

Preimplantation genetic testing for a family with usher syndrome through targeted sequencing and haplotype analysis

Background

Preimplantation genetic testing for monogenic defects (PGT-M) has been available in clinical practice. This study aimed to validate the applicability of targeted capture sequencing in developing personalized PGT-M assay.

Methods

One couple at risk of transmitting Usher Syndrome to their offspring was recruited to this study. Customized capture probe targeted at USH2A gene and 350 kb flanking region were designed for PGT-M. Eleven blastocysts were biopsied and amplified by using multiple displacement amplification (MDA) and capture sequencing. A hidden Markov model (HMM) assisted haplotype analysis was performed to deduce embryo’s genotype by using single nucleotide polymorphisms (SNPs) identified in each sample. The embryo without paternal rare variant was implanted and validated by conventional prenatal or postnatal diagnostic means.

Results

Four embryos were diagnosed as free of father’s rare variant, two were transferred and one achieved a successful pregnancy. The fetal genotype was confirmed by Sanger sequencing of fetal genomic DNA obtained by amniocentesis. The PGT-M and prenatal diagnosis results were further confirmed by the molecular diagnosis of the baby’s genomic DNA sample. The auditory test showed that the hearing was normal.

Conclusions

Targeted capture sequencing is an effective and convenient strategy to develop customized PGT-M assay.

Antisense Oligonucleotides for the Treatment of Inner Ear Dysfunction

Antisense oligonucleotides (ASOs) have shown potential as therapeutic molecules for the treatment of inner ear dysfunction. The peripheral sensory organs responsible for both hearing and equilibrium are housed within the inner ear. Hearing loss and vestibular balance problems affect a large portion of the population and limited treatment options exist. Targeting ASOs to the inner ear as a therapeutic strategy has unique pharmacokinetic and drug delivery opportunities and challenges. Here, we review ASO technology, delivery, disease targets, and other key considerations for development of this therapeutic approach.

Rho-kinase and PKCα Inhibition Induces Primary Cilia Elongation and Alters the Behavior of Undifferentiated and Differentiated Temperature-sensitive Mouse Cochlear Cells

Primary cilia, regulated via distinct signal transduction pathways, play crucial roles in various cellular behaviors. However, the full regulatory mechanism involved in primary cilia development during cellular differentiation is not fully understood, particularly for the sensory hair cells of the mammalian cochlea. In this study, we investigated the effects of the Rho-kinase inhibitor Y27632 and PKCα inhibitor GF109203X on primary cilia-related cell behavior in undifferentiated and differentiated temperature-sensitive mouse cochlear precursor hair cells (the conditionally immortalized US/VOT-E36 cell line). Our results indicate that treatment with Y27632 or GF109203X induced primary cilia elongation and tubulin acetylation in both differentiated and undifferentiated cells. Concomitant with cilia elongation, Y27632 treatment also increased Hook2 and cyclinD1 expression, while only Hook2 expression was increased after treatment with GF109203X. In the undifferentiated cells, we observed an increase in the number of S and G2/M stage cells and a decrease of G1 cells after treatment with Y27632, while the opposite was observed after treatment with GF109203X. Finally, while both treatments decreased oxidative stress, only treatment with Y27632, not GF109203X, induced cell cycle-dependent cell proliferation and cell migration.

Physical and Psychological Health in Persons with Deafblindness that is due to Usher Syndrome Type II

Introduction

The objectives of the study reported here were to describe the physical and psychological health of persons with Usher syndrome Type II (USH2) and to explore any differences in terms of gender.

Methods

The participants were recruited from the Swedish Usher database. In the first step, 122 persons received the questionnaire by mail, and 96 (aged 18–84, with a mean age of 55, 53% of whom were female) agreed to participate. The Health on Equal Terms questionnaire was used, which covered such items as health, living conditions, and social relationships. Results for the participants with USH2 were compared to those of a reference group of 5,738 persons who were drawn from a random sample of the Swedish population retrieved from the Swedish Public Health Institute. The odds ratio (adjusted for gender and age), and its 95% confidence interval were calculated.

Results

The participants with USH2 reported that their physical and psychological health was significantly poorer than that of the Swedish reference group. They revealed major problems involving headache, fatigue, depression, suicidal thoughts, and suicide attempts. For the male participants, the psychological differences were even more marked than those of the male reference group.

Discussion

The identification of factors associated with physical and psychological health and well-being is important for the design of future rehabilitation strategies for people with USH2. Special focus must be placed on the psychological well-being of men with USH2.

Implications for practitioners

The management of rehabilitation services for persons with USH2 calls for interdisciplinary teamwork to provide adequate resources to cope with the physical and psychological health issues demonstrated in this study.

Emerging Themes in PDZ Domain Signaling: Structure, Function, and Inhibition

Post-synaptic density-95, disks-large and zonula occludens-1 (PDZ) domains are small globular protein-protein interaction domains widely conserved from yeast to humans. They are composed of ∼90 amino acids and form a classical two α-helical/six β-strand structure. The prototypical ligand is the C-terminus of partner proteins; however, they also bind internal peptide sequences. Recent findings indicate that PDZ domains also bind phosphatidylinositides and cholesterol. Through their ligand interactions, PDZ domain proteins are critical for cellular trafficking and the surface retention of various ion channels. In addition, PDZ proteins are essential for neuronal signaling, memory, and learning. PDZ proteins also contribute to cytoskeletal dynamics by mediating interactions critical for maintaining cell-cell junctions, cell polarity, and cell migration. Given their important biological roles, it is not surprising that their dysfunction can lead to multiple disease states. As such, PDZ domain-containing proteins have emerged as potential targets for the development of small molecular inhibitors as therapeutic agents. Recent data suggest that the critical binding function of PDZ domains in cell signaling is more than just glue, and their binding function can be regulated by phosphorylation or allosterically by other binding partners. These studies also provide a wealth of structural and biophysical data that are beginning to reveal the physical features that endow this small modular domain with a central role in cell signaling.

Photoreceptor actin dysregulation in syndromic and non-syndromic retinitis pigmentosa

Retinitis pigmentosa (RP) is the leading cause of inherited blindness. RP is a genetically heterogeneous disorder, with more than 100 different causal genes identified in patients. Central to disease pathogenesis is the progressive loss of retinal photoreceptors. Photoreceptors are specialised sensory neurons that exhibit a complex and highly dynamic morphology. The highly polarised and elaborated architecture of photoreceptors requires precise regulation of numerous cytoskeletal elements. In recent years, significant work has been placed on investigating the role of microtubules (specifically, the acetylated microtubular axoneme of the photoreceptor connecting cilium) and their role in normal photoreceptor function. This has been driven by the emerging field of ciliopathies, human diseases arising from mutations in genes required for cilia formation or function, of which RP is a frequently reported phenotype. Recent studies have highlighted an intimate relationship between cilia and the actin cystoskeleton. This review will focus on the role of actin in photoreceptors, examining the connection between actin dysregulation in RP.

Generation of a human iPSC line, INMi002-A, carrying the most prevalent USH2A variant associated with Usher syndrome type 2

We generated an induced pluripotent stem cell (iPSC) line using dermal fibroblasts from a patient with Usher syndrome type 2 (USH2). This individual was homozygous for the most prevalent variant reported in the USH2A gene, c.2299delG localized in exon 13. Reprogramming was performed using the non-integrative Sendai virus reprogramming method and the human OSKM transcription factor cocktail under feeder-free culture conditions. This iPSC line will be an invaluable tool for studying the pathophysiology of USH2 and for testing the efficacy of novel treatments.

Generation of an iPSC line, INMi001-A, carrying the two most common USH2A mutations from a compound heterozygote with non-syndromic retinitis pigmentosa

We generated an induced pluripotent stem cell (iPSC) line from a patient with non-syndromic retinitis pigmentosa who is a compound heterozygote for the two most frequent USH2A variants, c.2276G > T and c.2299delG localized in exon 13. Patient fibroblasts were reprogrammed using the non-integrative Sendai virus reprogramming method and the human OSKM transcription factor cocktail. The generated cells were pluripotent and genetically stable. This iPSC line will be an important tool for studying the pathogenesis of these USH2A mutations and for developing treatments that, due their high prevalence, will target a large patient population.

Auditory disorders and future therapies with delivery systems

Auditory function takes a major part in human life. While sensorineural hearing loss is related with many factors including genetic disorders, age and noise, the clear causes are not well understood. Even more, the currently available treatments with drugs cause side effects, which thus are considered suboptimal. Here, we communicate the delivery systems with biomaterials that can be possible therapeutic options to restore hearing and vestibular functions. We introduce briefly the various pathological factors related with hearing loss and the limitation of current therapies, detail the recent studies on delivery systems including nanoparticles and hydrogels and discuss future clinical availability.

Usher Syndrome and Color Vision

PURPOSE

The aim of this study is to report on the results of color vision testing in a European cohort of patients with Usher syndrome (USH). We describe the results in relation to Usher type (USH1 and USH2), age and visual acuity.

METHODS AND METHODS

The color vision of 220 genetically confirmed adult USH patients, aged 18-70 years, was analyzed with one of three methods: the Farnsworth D-15 Dichotomous test (D-15) along with the Lanthony desaturated 15 Hue tests (D-15d), the Roth 28-Hue test, or the Ishihara 14-plate test. Visual acuity was measured with either the ETDRS or the SNELLEN charts. The Confusion index, the Selectivity index and the Confusion angle were calculated for the panel tests and used for analysis. The numbers of plates that could not be read were analyzed for the Ishihara test.

RESULTS

For the panel tests, the degree of color loss (Confusion index) is similar in both subtypes of USH, but the polarization of error scores (Selectivity index) is significantly lower in USH1 than USH2, showing more diffuse errors than those found in USH2. There is no significant correlation between logMAR visual acuity and the Confusion or the Selectivity indices. Additionally, we find a significant correlation between patient age and the degree and the polarity of the loss only in USH2. There was no difference between USH1 and USH2 in the results of the Ishihara test.

CONCLUSIONS

The examination of color vision in patients with USH shows a significant difference in the pattern of color vision loss in USH1 and USH2 patients, but not in the severity of the loss. In USH2, we find a correlation between patient age and the degree and the polarity of the loss. These results may be due to differences in the pathogenesis of retinal dystrophy in USH1 and USH2.

Inframe deletion of human ESPN is associated with deafness, vestibulopathy and vision impairment

BACKGROUND

Usher syndrome (USH) is a neurosensory disorder characterised by deafness, variable vestibular areflexia and vision loss. The aim of the study was to identify the genetic defect in a Pakistani family (PKDF1051) segregating USH.

METHODS

Genome-wide linkage analysis was performed by using an Illumina linkage array followed by Sanger and exome sequencing. Heterologous cells and mouse organ of Corti explant-based transfection assays were used for functional evaluations. Detailed clinical evaluations were performed to characterise the USH phenotype.

RESULTS

Through homozygosity mapping, we genetically linked the USH phenotype segregating in family PKDF1051 to markers on chromosome 1p36.32-p36.22. The locus was designated USH1M. Using a combination of Sanger sequencing and exome sequencing, we identified a novel homozygous 18 base pair inframe deletion in ESPN. Variants of ESPN, encoding the actin-bundling protein espin, have been previously associated with deafness and vestibular areflexia in humans with no apparent visual deficits. Our functional studies in heterologous cells and in mouse organ of Corti explant cultures revealed that the six deleted residues in affected individuals of family PKDF1051 are essential for the actin bundling function of espin demonstrated by ultracentrifugation actin binding and bundling assays. Funduscopic examination of the affected individuals of family PKDF1051 revealed irregular retinal contour, temporal flecks and disc pallor in both eyes. ERG revealed diminished rod photoreceptor function among affected individuals.

CONCLUSION

Our study uncovers an additional USH gene, assigns the USH1 phenotype to a variant of ESPN and provides a 12th molecular component to the USH proteome.

Identification of two novel compound heterozygous mutations of ADGRV1 in a Chinese family with Usher syndrome type IIC

BACKGROUND

To describe the clinical and genetic findings in a Chinese family with three sibs diagnosed with Usher syndrome type IIC.

MATERIALS AND METHODS

Four members received ophthalmic and otologic tests to ascertain the clinical characteristics. According to the clinical phenotype, we focused attention on a total of 658 genes associated with them. We screened the possible pathogenic mutation sites, used Sanger to exclude the false positive and verified whether there were co-segregated among the family members.

RESULTS

Typical fundus features found in the proband supported the diagnosis of retinitis pigmentosa (RP). Audiometric test indicated moderate to severe sensorineural hearing impairment while the vestibular function was normal. Whole-exome sequencing identified the presence of two novel compound heterozygous mutations in ADGRV1, a known gene responsible for Usher syndrome type IIC. Mutationc.15008delG/p.Gly5003AlafsTer13 was inherited from the mother while c.18383_18386dupACAG/p.His6130GlnfsTer84 was inherited from the father, and they were co-segregated with the disease phenotype in the family.

CONCLUSIONS

The mutations found in our study not only broaden the mutation spectrum of ADGRV1, but also provide assistances for future genetic diagnosis and treatment for Usher syndrome patients.