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© 2020, Piro-Mégy et al., Mutations in genes encoding components of the mitochondrial DNA (mtDNA) replication machinery cause mtDNA depletion syndromes (MDSs), which associate ocular features with severe neurological syndromes. Here, we identified heterozygous missense mutations in single-strand binding protein 1 (SSBP1) in 5 unrelated families, leading to the R38Q and R107Q amino acid changes in the mitochondrial single-stranded DNA-binding protein, a crucial protein involved in mtDNA replication. All affected individuals presented optic atrophy, associated with foveopathy in half of the cases. To uncover the structural features underlying SSBP1 mutations, we determined a revised SSBP1 crystal structure. Structural analysis suggested that both mutations affect dimer interactions and presumably distort the DNA-binding region. Using patient fibroblasts, we validated that the R38Q variant destabilizes SSBP1 dimer/tetramer formation, affects mtDNA replication, and induces mtDNA depletion. Our study showing that mutations in SSBP1 cause a form of dominant optic atrophy frequently accompanied with foveopathy brings insights into mtDNA maintenance disorders., This study was supported by the Spanish Ministry of Science, Innovation and Universities, MINECO (BFU2015-70645-R, RTI2018-101015-B-100 to MS), the Generalitat de Catalunya (2014-SGR-997 and 2017-SGR-1192 to MS), and the European Union (FP7-HEALTH-2012-306029-2 to MS). ATS was awarded with an FPU fellowship from the Ministry of Education, Professional Formation (MEFP). The Structural Biology Unit at IBMB-CSIC is a “Maria de Maeztu” Unit of Excellence awarded by MINECO (MDM-2014-0435). This work was supported by the “Prinses Beatrix Spierfonds” and the “Stichting Spieren voor Spieren” (W.OR15-05 to JNS).

Purpose: Usher syndrome (USH) is a multisensory deficiency involving vision, hearing and the vestibular system. The purpose of this study is to report on the functional data (i.e. electroretinography, visual fields, visual acuity) of patients with retinitis pigmentosa (RP) due to Usher syndrome that were collected in a multicentre European study (TREATRUSH). Methods: A total of 268 genetically confirmed USH patients underwent electrophysiological examinations in the context of multimodal ophthalmological examination in the study (75 USH1, 189 USH2 and four USH3). Full-field electroretinography (ERG) was performed according to ISCEV standards, visual field determination was carried out with either the Octopus or Goldmann perimeters and visual acuity was examined with either ETDRS or Snellen charts. The data were compared between USH subtypes (USH1/USH2/USH3) and correlated with age. Results: Visual acuity decreases significantly with age for both USH1 and USH2 (p < 0.001), without a difference between the two cohorts. When corrected for age, the preserved kinetic visual field was significantly larger in USH2 than in USH1 (p = 0.04). Furthermore, the preserved kinetic visual field area showed a significant decrease with age (based on an exponential fit) in both USH1 and USH2 (p < 0.001). In USH1 patients, however, the visual field was already vastly reduced at an early age. The ERG results were abnormal in all patients. Detectable data for scotopic ERG were obtained from nine patients, and data of photopic ERG were obtained from 24 patients, without a difference between USH1 and USH2 subtypes. Conclusions: There are differences in the phenotypes of RP in USH subtypes, most visible in the progression of visual fields between USH1 and USH2. The perimetric reduction occurs earlier in USH1 than in USH2. In both subtypes, visual acuity decreases significantly with age and the ERG is not detectable already at early ages. Purpose: Usher syndrome (USH) is a multisensory deficiency involving vision, hearing and the vestibular system. The purpose of this study is to report on the functional data (i.e. electroretinography, visual fields, visual acuity) of patients with retinitis pigmentosa (RP) due to Usher syndrome that were collected in a multicentre European study (TREATRUSH). Methods: A total of 268 genetically confirmed USH patients underwent electrophysiological examinations in the context of multimodal ophthalmological examination in the study (75 USH1, 189 USH2 and four USH3). Full-field electroretinography (ERG) was performed according to ISCEV standards, visual field determination was carried out with either the Octopus or Goldmann perimeters and visual acuity was examined with either ETDRS or Snellen charts. The data were compared between USH subtypes (USH1/USH2/USH3) and correlated with age. Results: Visual acuity decreases significantly with age for both USH1 and USH2 (p < 0.001), without a difference between the two cohorts. When corrected for age, the preserved kinetic visual field was significantly larger in USH2 than in USH1 (p = 0.04). Furthermore, the preserved kinetic visual field area showed a significant decrease with age (based on an exponential fit) in both USH1 and USH2 (p < 0.001). In USH1 patients, however, the visual field was already vastly reduced at an early age. The ERG results were abnormal in all patients. Detectable data for scotopic ERG were obtained from nine patients, and data of photopic ERG were obtained from 24 patients, without a difference between USH1 and USH2 subtypes. Conclusions: There are differences in the phenotypes of RP in USH subtypes, most visible in the progression of visual fields between USH1 and USH2. The perimetric reduction occurs earlier in USH1 than in USH2. In both subtypes, visual acuity decreases significantly with age and the ERG is not detectable already at early ages.

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. 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 18-70years, 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.

International audience; Night vision requires signaling from rod photoreceptors to adjacent bipolar cells in the retina. Mutations in the genes NYX and GRM6, expressed in ON bipolar cells, lead to a disruption of the ON bipolar cell response. This dysfunction is present in patients with complete X-linked and autosomal-recessive congenital stationary night blindness (CSNB) and can be assessed by standard full-field electroretinography (ERG), showing severely reduced rod b-wave amplitude and slightly altered cone responses. Although many cases of complete CSNB (cCSNB) are caused by mutations in NYX and GRM6, in~60% of the patients the gene defect remains unknown. Animal models of human diseases are a good source for candidate genes, and we noted that a cCSNB phenotype present in homozygous Appaloosa horses is associated with downregulation of TRPM1. TRPM1, belonging to the family of transient receptor potential channels, is expressed in ON bipolar cells and therefore qualifies as an excellent candidate. Indeed, mutation analysis of 38 patients with CSNB identified ten unrelated cCSNB patients with 14 different mutations in this gene. The mutation spectrum comprises missense, splice-site, deletion, and nonsense mutations. We propose that the cCSNB phenotype in these patients is due to the absence of functional TRPM1 in retinal ON bipolar cells.