Characterization of the ternary Usher syndrome SANS/ush2a/whirlin protein complex.

The Usher syndrome (USH) is the most common form of inherited deaf-blindness, accompanied by vestibular dysfunction. Due to the heterogeneous manifestation of the clinical symptoms, three USH types (USH1-3) and additional atypical forms are distinguished. USH1 and USH2 proteins have been shown to function together in multiprotein networks in photoreceptor cells and hair cells. Mutations in USH proteins are considered to disrupt distinct USH protein networks and finally lead to the development of USH.To get novel insights into the molecular pathomechanisms underlying USH, we further characterize the periciliary USH protein network in photoreceptor cells. We show the direct interaction between the scaffold protein SANS (USH1G) and the transmembrane adhesion protein ush2a and that both assemble into a ternary USH1/USH2 complex together with the PDZ-domain protein whirlin (USH2D) via mutual interactions. Immunohistochemistry and proximity ligation assays demonstrate co-localization of complex partners and complex formation, respectively, in the periciliary region, the inner segment and at the synapses of rodent and human photoreceptor cells. Protein-protein interaction assays and co-expression of complex partners reveal that pathogenic mutations in USH1G severely affect formation of the SANS/ush2a/whirlin complex. Translational read-through drug treatment, targeting the c.728C > A (p.S243X) nonsense mutation, restored SANS scaffold function. We conclude that USH1 and USH2 proteins function together in higher order protein complexes. The maintenance of USH1/USH2 protein complexes depends on multiple USH1/USH2 protein interactions, which are disrupted by pathogenic mutations in USH1G protein SANS.

PEX6 is Expressed in Photoreceptor Cilia and Mutated in Deafblindness with Enamel Dysplasia and Microcephaly.

Deafblindness is part of several genetic disorders. We investigated a consanguineous Egyptian family with two siblings affected by congenital hearing loss and retinal degeneration, initially diagnosed as Usher syndrome type 1. At teenage, severe enamel dysplasia, developmental delay, and microcephaly became apparent. Genome-wide homozygosity mapping and whole-exome sequencing detected a homozygous missense mutation, c.1238G>T (p.Gly413Val), affecting a highly conserved residue of peroxisomal biogenesis factor 6, PEX6. Biochemical profiling of the siblings revealed abnormal and borderline plasma phytanic acid concentration, and cerebral imaging revealed white matter disease in both. We show that Pex6 localizes to the apical extensions of secretory ameloblasts and differentiated odontoblasts at early stages of dentin synthesis in mice, and to cilia of retinal photoreceptor cells. We propose PEX6, and possibly other peroxisomal genes, as candidate for the rare cooccurrence of deafblindness and enamel dysplasia. Our study for the first time links peroxisome biogenesis disorders to retinal ciliopathies.

Phosphoribosylpyrophosphate synthetase superactivity and recurrent infections is caused by a p.Val142Leu mutation in PRS-I.

We identified a novel missense mutation, c.424G>C (p.Val142Leu) in PRPS1 in a patient with uric acid overproduction without gout but with developmental delay, hypotonia, hearing loss, and recurrent respiratory infections. The uric acid overproduction accompanying this combination of symptoms suggests that the patient presented with phosphoribosylpyrophosphate (PRPP) synthetase superactivity, but recurrent infections have not been associated with superactivity until now. However, recurrent infections are a prominent feature of patients with Arts syndrome, which is caused by PRPS1 loss-of-function mutations, indicating that the patient reported here has an intermediate phenotype. Molecular modeling predicts that the p.Val142Leu change affects both allosteric sites that are involved in inhibition of PRPS1 and the ATP-binding site, which suggests that this substitution can result both in a gain-of-function and loss-of-function of PRPP synthetase. This finding is in line with the normal PRPP synthetase activity in fibroblasts and the absence of activity in erythrocytes of the present patient. We postulate that the overall effect of the p.Val142Leu change on protein activity is determined by the cell type, being a gain-of-function in proliferating cells and a loss-of-function in postmitotic cells. Our results show that missense mutations in PRPS1 can cause a continuous spectrum of features ranging from progressive non-syndromic postlingual hearing impairment to uric acid overproduction, neuropathy, and recurrent infections depending on the functional sites that are affected.

The development of the International Classification of Functioning, Disability and Health Core Sets for deafblindness: A study protocol.

BACKGROUND: Individuals with deafblindness experience a combination of hearing and vision impairments. The World Health Organization has developed a global framework referred to as the International Classification of Functioning, Disability and Health (ICF) to describe health and functioning. From the full ICF classification, a selection of categories, referred to as ICF Core Sets, provide users with a tool to describe functioning and disability in specific health conditions. There has been no ICF Core Set created for deafblindness. Given that core sets are instrumental in improving clinical practice, research, and service delivery, the aim of this study is to develop an ICF Core Set for deafblindness. METHODS: As part of the preparatory phase in the ICF Core Set development, there are four studies that will be conducted. This includes the [1] systematic literature review that examines the researcher's perspective, [2] qualitative study focusing on the individuals with deafblindness experience, [3] experts survey that looks at health professional's perspective, and [4] empirical study that examines the clinical perspective. The studies will be conducted using the principles outlined by the ICF Research Branch for the development of ICF Core Sets. The systematic literature review protocol was submitted for registration on PROSPERO CRD42021247952. DISCUSSION: An ICF Core Set created for deafblindness will benefit individuals living with deafblindness who are often excluded from social participation, policies, and services. An ICF Core Set for deafblindness will have a significant impact on healthcare professionals, policymakers, researchers, service providers and individuals with deafblindness by facilitating communication among all stakeholder to support the functioning of those with deafblindness.

PRPS1 loss-of-function variants, from isolated hearing loss to severe congenital encephalopathy: New cases and literature review.

We describe two sporadic and two familial cases with loss-of-function variants in PRPS1, which is located on the X chromosome and encodes phosphoribosyl pyrophosphate synthetase 1 (PRS-1). We illustrate the clinical variability associated with decreased PRS-1 activity, ranging from mild isolated hearing loss to severe encephalopathy. One of the variants we identified has already been reported with a phenotype similar to our patient's, whereas the other three were unknown. The clinical and biochemical information we provide will hopefully contribute to gain insight into the correlation between genotype and phenotype of this rare condition, both in females and in males. Moreover, our observation of a new family in which hemizygous males display hearing loss without any neurological or ophthalmological symptoms prompts us to suggest analysing PRPS1 in cases of isolated hearing loss. Eventually, PRPS1 variants should be considered as a differential diagnosis of mitochondrial disorders.

Functional analysis of a novel mutation in the TIMM8A gene that causes deafness-dystonia-optic neuronopathy syndrome.

BACKGROUND: The rare, X-linked neurodegenerative disorder, Mohr-Tranebjaerg syndrome (also called deafness-dystonia-optic neuronopathy [DDON] syndrome), is caused by mutations in the TIMM8A gene. DDON syndrome is characterized by dystonia, early-onset deafness, and various other neurological manifestations. The TIMM8A gene product localizes to the intermembrane space in mitochondria where it functions in the import of nuclear-encoded proteins into the mitochondrial inner membrane. Frameshifts or premature stops represent the majority of mutations in TIMM8A that cause DDON syndrome. However, missense mutations have also been reported that result in loss of the TIMM8A gene product. METHODS: We report a novel TIMM8A variant in a patient with DDON syndrome that alters the initiation codon and employed functional analyses to determine the significance of the variant and its impact on mitochondrial morphology. RESULTS: The novel base change in the TIMM8A gene (c.1A>T, p.Met1Leu) results in no detectable protein and a reduction in TIMM8A transcript abundance. We observed a commensurate decrease in the steady-state level of the Tim13 protein (the binding partner of Tim8a) but no decrease in TIMM13 transcripts. Patient fibroblasts exhibited elongation and/or increased fusion of mitochondria, consistent with prior reports. CONCLUSION: This case expands the spectrum of mutations that cause DDON syndrome and demonstrates effects on mitochondrial morphology that are consistent with prior reports.

Participation experiences of people with deafblindness or dual sensory loss: A scoping review of global deafblind literature.

BACKGROUND: Deafblindness, also known as dual sensory loss, is a varying combination of visual and hearing impairment in the same individual. Interest in this topic has increased recently due to evidence suggesting an increase in prevalence of this condition among older adults. Persons with deafblindness frequently experience participation barriers and social isolation. Developing an understanding of their experiences can inform the design of programs and policies to enhance participation of people with deafblindness in society. OBJECTIVE: To identify and summarize available research literature on participation experiences of people with deafblindness or dual sensory loss. METHODS: A comprehensive literature search of eight databases (CINAHL/EBSCO, Embase, ERIC, Global Health, MEDLINE, ProQuest, PsycINFO, PubMed) was performed in accordance with the Preferred Reporting Items for Systematic Reviews (PRISMA) during January 2017 and last updated in June 2017. In addition, non-peer reviewed (grey) literature was also retrieved in the form of online published reports of research projects by 16 deafblind-specific organizations across the globe. To be included, sources had to be published after 1990, had persons with deafblindness as the focal population, and focused on their participation experiences. RESULTS: A total 1172 sources were identified of which 54 studies were included. The findings reveal that persons with deafblindness, regardless of origin of their impairment, experience difficulty in communication, mobility, daily living functioning, and social interactions. While these experiences may vary between individuals with congenital versus acquired conditions, they generally feel socially isolated, insecure and uncertain about their future. CONCLUSION: Participation experiences of persons with deafblindness are shaped by dynamic interactions between personal factors (such as onset and type of impairments) and environmental influences (such as attitude, technology, and supports). A better understanding of participation experiences may help professionals in placing emphasis on affected participation domains to design services to enhance participation of people with deafblindness.

Dystonia-deafness syndrome caused by ACTB p.Arg183Trp heterozygosity shows striatal dopaminergic dysfunction and response to pallidal stimulation.

BACKGROUND: Dystonia-deafness syndrome is a well-known clinical entity, with sensorineural deafness typically manifesting earlier than dystonia. ACTB p.Arg183Trp heterozygosity has been reported in six patients to cause combined infant-onset deafness and dystonia manifesting in adolescence or young adulthood. Three of these have received beneficial pallidal stimulation. Brain imaging to assess striatal function has not been reported previously, however. Nor has a comprehensive hypothesis been presented for how the pleiotropic manifestations of this specific beta-actin gene mutation originate developmentally. CASE PRESENTATION: A 19-year-old girl with congenital mild dysmorphic facial features, cochlear implants for infant-onset deafness, and mild cognitive and emotional disability, presented with an adolescent-onset, severe generalized dystonia. Brain MRI and multiple single gene sequencing were inconclusive. Due to life-threatening dystonia, we implanted a neurostimulation device, targeting the postero-ventral internal pallidum bilaterally. The Burke-Fahn-Marsden Dystonia Rating Scale motor/disability scores improved from 87/25 to 21/13 at 2.5 months postoperatively, 26/14 at 3 years, and 30/14 at 4 years. Subsequent whole exome sequencing identified heterozygosity for the ACTB p.Arg183Trp variant. Brain imaging included 123I-ioflupane single photon emission computed tomography (Dopamine Transporter-SPECT), SPECT with 123I-epidepride (binds to dopamine type 2-receptors) and 18 Fluoro-Deoxy-Glucose (FDG)-PET. Both Epidepride-SPECT and FDG-PET showed reduced tracer uptake in the striatum bilaterally, particularly in the putamen. DaT-SPECT was slightly abnormal. CONCLUSIONS: In this patient with dystonia-deafness syndrome caused by ACTB p.Arg183Trp heterozygosity, unprecedented brain imaging findings strongly indicate striatal neuronal/dopaminergic dysfunction as the underlying cause of the dystonia. Pallidal stimulation provided a substantial improvement of the severe generalized dystonia, which is largely sustained at 4-year follow-up, and we advise this treatment to be considered in such patients. We hypothesize that the pleiotropic manifestations of the dystonia-deafness syndrome caused by this mutation derive from diverse developmental functions of beta-actin in neural crest migration and proliferation (facial dysmorphogenesis), hair cell stereocilia function (infant-onset deafness), and altered synaptic activity patterns associated with pubertal changes in striatal function (adolescent-onset dystonia). The temporal differences in developmental onset are likely due to varying degrees of susceptibility and of compensatory upregulation of other actin variants in the affected structures.