Biallelic Mutations in GNB3 Cause a Unique Form of Autosomal-Recessive Congenital Stationary Night Blindness.

Congenital stationary night blindness (CSNB) is a heterogeneous group of non-progressive inherited retinal disorders with characteristic electroretinogram (ERG) abnormalities. Riggs and Schubert-Bornschein are subtypes of CSNB and demonstrate distinct ERG features. Riggs CSNB demonstrates selective rod photoreceptor dysfunction and occurs due to mutations in genes encoding proteins involved in rod phototransduction cascade; night blindness is the only symptom and eye examination is otherwise normal. Schubert-Bornschein CSNB is a consequence of impaired signal transmission between the photoreceptors and bipolar cells. Schubert-Bornschein CSNB is subdivided into complete CSNB with an ON bipolar signaling defect and incomplete CSNB with both ON and OFF pathway involvement. Both subtypes are associated with variable degrees of night blindness or photophobia, reduced visual acuity, high myopia, and nystagmus. Whole-exome sequencing of a family screened negative for mutations in genes associated with CSNB identified biallelic mutations in the guanine nucleotide-binding protein subunit beta-3 gene (GNB3). Two siblings were compound heterozygous for a deletion (c.170_172delAGA [p.Lys57del]) and a nonsense mutation (c.1017G>A [p.Trp339(∗)]). The maternal aunt was homozygous for the nonsense mutation (c.1017G>A [p.Trp339(∗)]). Mutational analysis of GNB3 in a cohort of 58 subjects with CSNB identified a sporadic case individual with a homozygous GNB3 mutation (c.200C>T [p.Ser67Phe]). GNB3 encodes the ß subunit of G protein heterotrimer (Gαßγ) and is known to modulate ON bipolar cell signaling and cone transducin function in mice. Affected human subjects showed an unusual CSNB phenotype with variable degrees of ON bipolar dysfunction and reduced cone sensitivity. This unique retinal disorder with dual anomaly in visual processing expands our knowledge about retinal signaling.

Frequency and clinical pattern of vitelliform macular dystrophy caused by mutations of interphotoreceptor matrix IMPG1 and IMPG2 genes.

PURPOSE: To assess the frequency of and to characterize the clinical spectrum and optical coherence tomography findings of vitelliform macular dystrophy linked to IMPG1 and IMPG2, 2 new causal genes expressed in the interphotoreceptor matrix. DESIGN: Retrospective epidemiologic, clinical, electrophysiologic, and molecular genetic study. PARTICIPANTS: The database of a national referral center specialized in genetic sensory diseases was screened for patients with a macular vitelliform dystrophy without identified mutation or small deletion or large rearrangement in BEST1 and PRPH2 genes. Forty-nine families were included. METHODS: Clinical, imaging, and electro-oculogram findings were reviewed. Mutation screening of IMPG1 and IMPG2 genes were performed systematically. MAIN OUTCOME MEASURES: Frequency, inheritance, and clinical pattern of vitelliform dystrophy associated with IMPG1 and IMPG2 mutations were characterized. RESULTS: IMPG1 was the causal gene in 3 families (IMPG1 1-3, 11 patients) and IMPG2 in a fourth family (2 patients). With an autosomal dominant transmission, families 1 and 2 had the c.713T→G (p.Leu238Arg) mutation in IMPG1 and family 4 had the c.3230G→T (p.Cys1077Phe) mutation in IMPG2. Patients with IMPG1 or IMPG2 mutations had a late onset and moderate visual impairment (mean visual acuity, 20/40; mean age of onset, 42 years), even in the sporadic case of family 3 with a presumed recessive transmission (age at onset, 38 years; mean visual acuity, 20/50). Drusen-like lesions adjacent to the vitelliform deposits were observed in 9 of 13 patients. The vitelliform material was above the retinal pigment epithelium (RPE) at any stage of the macular dystrophy, and this epithelium was well preserved and maintained its classical reflectivity on spectral-domain optical coherence tomography (SD-OCT). Electro-oculogram results were normal or borderline in 9 cases. CONCLUSIONS: IMPG1 and IMPG2 are new causal genes in 8% of families negative for BEST1 and PRPH2 mutations. These genes should be screened in adult-onset vitelliform dystrophy with (1) moderate visual impairment, (2) drusen-like lesions, (3) normal reflectivity of the RPE line on SD-OCT, and (4) vitelliform deposits located between ellipsoid and interdigitation lines on SD-OCT. These clinical characteristics are not observed in the classical forms of BEST1 or PRPH2 vitelliform dystrophies.

Early-onset foveal involvement in retinitis punctata albescens with mutations in RLBP1.

IMPORTANCE: Retinitis punctata albescens (RPA) is an autosomal recessive form of retinitis pigmentosa characterized by white dotlike deposits in the fundus, in most cases caused by mutations in RLBP1. OBJECTIVE: To study disease progression and visual function in RPA. DESIGN: We performed clinical and molecular investigations in patients with RPA at various ages, from November 5, 2003, through June 20, 2012, with no planned patient follow-up. SETTING: The National Reference Center for Genetic Sensory Diseases (Montpellier). PARTICIPANTS: Eleven patients with RPA (mean age, 24 [range, 3-39] years) from 7 families and 11 control subjects undergoing evaluation. EXPOSURE: Optical coherence tomography measurements. MAIN OUTCOMES AND MEASURES: Screening for mutations by polymerase chain reaction sequencing of the 9 RLBP1 exons. Patients underwent standard ophthalmic examination, fundus imaging, autofluorescence testing, Goldmann visual field measurement, optical coherence tomography, adaptive optics-based infrared fundus ophthalmoscopy, dark adaptometry, and electroretinography. RESULTS: We found 2 novel RLBP1 mutations (p.Tyr111X and p.Arg9Cys), and 8 patients from Morocco were homozygous for the recurrent 7.36-kilobase RLBP1 deletion of exons 7 through 9. All patients had night blindness (before age 6 years in 10). The dotlike deposits were generally dense but could be rare, appearing in adaptive optics as elongated structures with variable orientation and no foveal involvement. We found no specific refractive error, and visual acuity varied widely from normal (1.2) to counting fingers. Variable degrees of visual field impairment were present, and all patients had severely decreased electroretinographic responses with predominant rod impairment. No correlation between visual acuity (P = .27) or visual field and age (P = .08) was present. On optical coherence tomography, the mean (SD) central foveal (122 [23] vs 187 [30] µm in controls) and foveal (147 [19] vs 217 [17] µm) thicknesses were significantly (P < .01) decreased, independently of age, whereas the retinal thickness at the 3- and 6-mm rings around the fovea progressively decreased with age. Mean (SD) cone number was normal in 1 patient aged 13 years (21,000/mm² [2000/mm²]) but dropped to 10,500/mm² (5244/mm²), 8667/mm² (2944/mm²), and 5833/mm² (983/mm²) in 3 other patients aged 39, 32, and 29 years, respectively. CONCLUSIONS AND RELEVANCE: Patients with RPA show variable degrees of foveal cone death, even at an early stage. This finding has implications for future treatment.