Usher syndrome is the leading cause of inherited deaf-blindness, with type 2 (Usher syndrome type 2, USH2) being the most common form. USH2A, ADGRV1, and WHRN are the three known USH2 causative genes, which are also linked to isolated retinal degeneration and hearing loss. These genes encode usherin, ADGRV1, and whirlin, respectively, collectively called USH2 proteins. These proteins form a multiprotein complex (USH2 complex) at the periciliary membrane in retinal photoreceptors and at the stereociliary ankle link in inner ear hair cells. The molecular function of the USH2 complex and its disease mechanisms are poorly understood. Currently, there is no cure for diseases caused by mutations in the three USH2 genes. In this study, we employed multiple affinity purification methods combined with mass spectrometry to systematically identify the interaction partners of USH2 proteins in the retina. The ADGRV1 intracellular bait pulled down proteins involved in actin-based cell projections, the chaperone-containing TCP-1 complex, and the Bardet-Biedl syndrome complex. The extracellular domains of ADGRV1 and usherin pulled down proteins related to peptidase regulation, collagen biosynthesis and modification, and elastic fiber formation. The EAR/EPTP repeats of ADGRV1 specifically pulled down TGFβ signaling proteins. Further immunoprecipitation experiments identified, with high confidence, Gαi and Gαq as ADGRV1-interacting proteins, and retinal degeneration and ciliary proteins as interaction partners of USH2 proteins. We also demonstrated that the usherin extracellular domains interact with each other and with ADGRV1. Overall, these findings suggest that the USH2 complex connects the extracellular matrix (ECM) to the intracellular actin network, signals through Gαi and Gαq, and participates in ECM remodeling, TGFβ signaling, cell adhesion, and ciliary function in photoreceptors.

Primary cilia are antenna-like sensory organelles present on almost all eukaryotic cells. Their sensory capacity relies on receptors, in particular G-protein-coupled receptors (GPCRs) which localize to the ciliary membrane. Here we show that ADGRV1, a member of the GPCR subfamily of adhesion GPCRs, is part of a large protein network, interacting with numerous proteins of a comprehensive ciliary proteome. ADGRV1 is localized to the base of prototypic primary cilia in cultured cells and the modified primary cilia of retinal photoreceptors, where it interacts with TRiC/CCT chaperonins and the Bardet Biedl syndrome (BBS) chaperonin-like proteins. Knockdown of ADGRV1, CCT2 and 3, and BBS6 result in common ciliogenesis phenotypes, namely reduced ciliated cells combined with shorter primary cilia. In addition, the localization of ADGRV1 to primary cilia depends on the activity of a co-complex of TRiC/CCT chaperonins and the BBS chaperonin-like proteins. In the absence of components of the TRiC/CCT-BBS chaperonin co-complex, ADGRV1 is depleted from the base of the primary cilium and degraded via the proteasome. Defects in the TRiC/CCT-BBS chaperonin may lead to an overload of proteasomal degradation processes and imbalanced proteostasis. Dysfunction or absence of ADGRV1 from primary cilia may underly the pathophysiology of human Usher syndrome type 2 and epilepsy caused by mutations in ADGRV1.

ObjectiveThis current cross-sectional study aimed to investigate the demographic characteristics and molecular epidemiology of patients with Usher syndrome in the Turkish population.MethodsPatients who were followed up with a preliminary diagnosis of Usher syndrome from various regions of the country were included in the study. After a review of patients' medical histories, all underwent ophthalmological and otorhinolaryngological examinations. Mutations reported in previous studies in MYO7A, PCDH15, USH1C, CDH23, and USH2A were investigated using Sanger sequencing.ResultsFourteen (29.2%) patients had Usher syndrome type 1 and 16 (33.3%) had type 2. Eighteen (37.5%) patients could not be typed. We detected mutations in MYO7A (c.1343 + 1 G > A) in seven patients (six heterozygous and one homozygous) from seven families clinically compatible with Usher syndrome type 2 (rather than Usher syndrome type 1, as was expected based on previous studies).ConclusionsOur preliminary findings suggest that the proportions of patients with Usher syndrome type 1 and Usher syndrome type 2 in the Turkish population were almost equal, and none of our patients was clinically compatible with Usher syndrome type 3. Although previous studies reported that mutations in MYO7A rarely caused Usher syndrome type 2, in the Turkish population, MYO7A alleles may be hypomorphic and manifest as a milder phenotype in Usher syndrome compared with other populations.

Inherited retinal diseases (IRDs) are a group of heterogeneous conditions leading to visual impairment and blindness with over 280 associated genes identified so far. This study aims to provide an initial characterization of the clinical and genetic landscape of IRDs in the United States with a cohort from Kentucky and contribute to the existing knowledge from studies in other regions. This single-academic center retrospective analysis was conducted on patients seen at the University of Kentucky Ophthalmic Genetic Services from January 2019 to March 2022 with a diagnosis of or concern for unspecified IRD and who underwent subsequent genetic testing with an IRD panel. The study included 366 subjects with a pre-genetic testing IRD diagnosis, with an age range from 9 to 87 years old and mean age of 42.11 years. The most common pre-genetic diagnoses were retinitis pigmentosa (RP) in 116 subjects (31.69%), referral for ‘concern for unspecified IRD’ in 107 subjects (29.23%), and macular dystrophy in 31 subjects (8.46%). The diagnostic yield of genetic testing for rod-cone dystrophy (RCD) cases was 83.89%. The five most common genetic testing confirmed diagnoses were RP, Usher syndrome type 2 (USH2A), Stargardt disease (STGD), Bardet-Biedl syndrome (BBS), and Usher syndrome type 1 (USH1). A total of 46 individual genes had pathogenic variants. The three most frequently pathogenic genes were RHO, USH2A, and ABCA4, with 5 pathogenic variants within RHO, 20 within USH2A, and 17 within ABCA4. Five novel variants were identified across the WFS1, ARSG, USH2A, ADGRV1, and PCDH15 genes. This study characterizes the genetic landscape of IRDs in a Kentucky cohort, with pathogenic variants in 46 genes, including five novel variants. These novel variants highlight the need for continued research to identify more population-specific variants. The findings highlight the value of genetic testing and contribute to advancing IRD research and care. ClinicalTrials.gov registration number: NCT06177977. First posted date: 12/20/2023. The online version contains supplementary material available at 10.1186/s12920-025-02186-5.

Whrn, encoding whirlin, is one of the genes highly relevant to Usher syndrome (USH) that has been known as an autosomal recessive genetic disorder that is characterized with sensorineural hearing loss with retinitis pigmentosa. Although recent studies on the other USH genes, PDZD7 and Ush1 g, showed a possibility of haploinsufficiency effect, the potential contribution of heterozygous Whrn loss to hearing loss remains unclear. To investigate the effect of Whrn haploinsufficiency, we conducted a longitudinal study assessing auditory function in heterozygous Whrn mutant (Whrn+/-) mice in which long isoform of Whrn was deleted by replacing exon 1 with Neo cassette without disturbing short isoform. The threshold of auditory brainstem responses (ABRs) was measured on 135 Whrn+/- mice and littermate 133 wild-type (WT) mice from 1 to 6 months of ages. From those data, the threshold from male and female were separately analyzed to investigate sex-dependent effect. To further investigate underlie mechanisms, hair cell death was investigated using immunohistostaining from 4 to 5 WT, 5 female Whrn+/-, and 7 male Whrn+/- mice at 4-5 months old. Hearing threshold was significantly increased with aging in Whrn+/- mice compared to WT controls. Both WT and Whrn+/- mice exhibited sex-dependent variations in hearing sensitivity. Notably, Whrn+/- males showed a progressive hearing loss with age, while Whrn+/- females exhibited elevated hearing thresholds as early as 1-2 month of age compared to WT females. These results provide evidence for a haploinsufficiency effect of Whrn on auditory function and highlight its potential role in progressive sensorineural hearing loss.