Genotype-Phenotype Correlations in RP1-Associated Retinal Dystrophies: A Multi-Center Cohort Study in JAPAN.

BACKGROUND: Little is known about genotype-phenotype correlations of RP1-associated retinal dystrophies in the Japanese population. We aimed to investigate the genetic spectrum of RP1 variants and provide a detailed description of the clinical findings in Japanese patients. METHODS: In total, 607 patients with inherited retinal diseases were examined using whole-exome/whole-genome sequencing (WES/WGS). PCR-based screening for an Alu element insertion (c.4052_4053ins328/p.Tyr1352AlafsTer9) was performed in 18 patients with autosomal-recessive (AR)-retinitis pigmentosa (RP) or AR-cone dystrophy (COD)/cone-rod dystrophy (CORD), including seven patients with heterozygous RP1 variants identified by WES/WGS analysis, and 11 early onset AR-RP patients, in whom no pathogenic variant was identified. We clinically examined 25 patients (23 families) with pathogenic RP1 variants, including five patients (five families) with autosomal-dominant (AD)-RP, 13 patients (11 families) with AR-RP, and seven patients (seven families) with AR-COD/CORD. RESULTS: We identified 18 pathogenic RP1 variants, including seven novel variants. Interestingly, the Alu element insertion was the most frequent variant (32.0%, 16/50 alleles). The clinical findings revealed that the age at onset and disease progression occurred significantly earlier and faster in AR-RP patients compared to AD-RP or AR-COD/CORD patients. CONCLUSIONS: Our results suggest a genotype-phenotype correlation between variant types/locations and phenotypes (AD-RP, AR-RP, and AR-COD/CORD), and the Alu element insertion was the most major variant in Japanese patients with RP1-associated retinal dystrophies.

Multimodal imaging analysis of macular dystrophy in patient with maternally inherited diabetes and deafness (MIDD) with m.3243A>G mutation.

Purpose: Maternally inherited diabetes and deafness (MIDD) is caused by a heteroplasmic m.3243A>G mutation in the mitochondrial DNA. The main ocular feature in MIDD is macular dystrophy. The purpose of this study was to identify the phenotypical characteristics of a patient with MIDD by multimodal high-resolution imaging analyses.Methods: A detailed history and ophthalmic examination were performed on a 39-year-old patient with MIDD. Multi-modal imaging included fundus photography, fundus autofluorescence imaging, fluorescein angiography, spectral-domain optical coherence tomography, OCT-angiography, and adaptive optics imaging. The PCR-invader and whole exome sequencing (WES) methods were performed on the DNA of the patient.Results: A 39-year-old woman with sensorineural hearing loss, diabetes mellitus presented with atrophic perifoveal changes and MIDD was suspected. The PCR-invader and WES methods showed that the patient had a m.3243A>G mutation in the mitochondrial DNA with 29% and 16.7% of the heteroplasmy in the peripheral blood, respectively. Morphological analyses revealed that the areas of photoreceptor degeneration and chorioretinal atrophy were present mainly in the perifoveal region. Multifocal ERGs showed that the perifoveal responses were reduced. Goldmann visual field was significant for a cecocentral scotoma in the right eye and an enlarged blind spot in the left eye. The central isopter was constricted bilaterally. The results of high-resolution retinal imaging by AO revealed that the densities of the cone photoreceptor were significantly reduced in the fovea where no obvious atrophy of the RPE and choroid was observed.Conclusions: Our findings indicate that WES analysis can be used to detect the m.3243A>G mutation in the mtDNA. The results of multimodal imaging analyses indicated that the primary dysfunction of the photoreceptors in the fovea might precede the dysfunction of the RPE in patient with MIDD.

High-resolution photoreceptor imaging analysis of patients with autosomal dominant retinitis pigmentosa (adRP) caused by HK1 mutation.

PURPOSE: The hexokinase 1 (HK1) gene encodes one of the four human hexokinases that play essential roles in glucose metabolism. Recently, several cases of E847K mutation in the HK1 gene were reported to cause inherited retinal dystrophy. The purpose of this study was to identify the phenotypical characteristics of patients with a recurrent E847K mutation in the HK1 gene. METHODS: Three generations of one family with autosomal dominant retinitis pigmentosa were examined. Whole exome sequencing was performed on the DNA. Fundus imaging by an adaptive optics fundus camera was used to obtain high-resolution photoreceptor images. RESULTS: Fundus examination of the proband showed degeneration of the mid-peripheral retina, and SD-OCT images showed an absence of the ellipsoid zone (EZ) and interdigitation zone (IZ) in the parafovea and more peripherally. SD-OCT images of the mother of the proband showed an absence of the EZ and IZ, and fundus autofluorescence images showed hypo-autofluorescence surrounding the macular region. One daughter of the proband had only mild night blindness, however, the density of the cone photoreceptors was reduced in the parafoveal region. Whole exome sequencing identified a heterozygous variant, E847K, in the HK1 gene. This variant was found to co-segregate with the disease in three family members. CONCLUSIONS: Although the systemic phenotypes were found to be associated with the HK1 mutations, only the E847K mutation can cause a non-syndromic photoreceptor degeneration. Our study strengthened the hypothesis that the amino acid E847 might play a critical role in the maintenance of the morphology and function of the photoreceptors.

Novel GUCY2D Variant (E843Q) at Mutation Hotspot Associated with Macular Dystrophy in a Japanese Patient.

BACKGROUND: The GUCY2D (guanylate cyclase 2D) gene encodes a photoreceptor guanylate cyclase (GC-E), that is predominantly expressed in the cone outer segments. Mutations in the GUCY2D lead to severe retinal disorders such as autosomal dominant cone-rod dystrophy (adCRD) and autosomal recessive Leber congenital amaurosis type 1. The purpose of this study was to identify the phenotype of a Japanese patient with a probably pathogenic GUCY2D variant. METHODS: Detailed ophthalmic examinations were performed, and whole exome sequencing was performed on DNA obtained from the patient. The variants identified by exome sequencing and targeted analysis were further confirmed by direct sequencing. RESULTS: A 47-year-old man had atrophic and pigmentary changes in the macula of both eyes. Amplitudes and implicit times on full-field electroretinograms (ERGs) were within normal limits; however, the densities of multifocal ERGs in the central area were reduced in both eyes. Whole exome sequencing identified heterozygous variant c.2527G>C, p.Glu843Gln in the GUCY2D gene within the mutation hot spot for adCRD. The allelic frequencies of this variant are extremely low and, according to American College of Medical Genetics and Genomics standards and guidelines, the variants are classified as likely pathogenic. CONCLUSIONS: This is the first report of a heterozygous variant, c.2527G>C, p.Glu843Gln, in the GUCY2D, in a patient presenting with mild macular dystrophy without a general reduction in cone function. Our findings expand the spectrum of the clinical phenotypes of GUCY2D-adCRD and help clarify the morphological and functional changes caused by defects of dimerization of GC-E in the phototransduction cascade.

Novel homozygous in-frame deletion of GNAT1 gene causes golden appearance of fundus and reduced scotopic ERGs similar to that in Oguchi disease in Japanese family.

Background: The GNAT1 gene encodes the alpha-subunit of transducin in rod photoreceptors and is an important part of the phototransduction cascade. Defects in GNAT1 are very rare but have been identified in autosomal dominant and recessive congenital stationary night blindness (CSNB) and autosomal recessive rod-cone dystrophy. The purpose of this study was to determine the phenotype-genotype relationship in a non-consanguineous Japanese family with a GNAT1 mutation.Methods: Detailed ophthalmic examinations were performed on the patients and their family members. Whole exome sequencing (WES) was applied to the DNA obtained from the family members. Sanger sequencing and co-segregation analyses were performed to identify the most likely pathogenic variant.Results: Two female (13- and 11-years) and one male (15-years) patients from a family had night blindness from their childhood. The fundus had a mild golden appearance regardless of the state of light- or dark-adaptation. Electroretinographic (ERG) analyses showed that the scotopic a-wave was extinguished, and the mixed rod-cone responses were severely reduced with an electronegative form in patients. The shapes of the dark-adapted ERGs were similar to those recorded from patients with Oguchi disease. We identified a homozygous in-frame deletion c.818_820delAGA, p.Lys273del in the GNAT1 gene. Variants were verified by Sanger sequencing and co-segregated with the disease in five members of the family.Conclusions: Our findings indicate that a recessive GNAT1 mutation found in this family could be the cause of the golden appearance of the fundus and negative ERGs with reduced a-waves, and nearly absent b-waves in the mixed rod-cone ERGs.

Novel mutations in the RS1 gene in Japanese patients with X-linked congenital retinoschisis.

X-linked congenital retinoschisis (XLRS) is an inherited retinal disorder characterized by reduced central vision and schisis of the macula and peripheral retina. XLRS is caused by mutations in the RS1 gene. We have identified 37 different mutations in the RS1 gene, including 12 novel mutations, in 67 Japanese patients from 56 XLRS families. We present clinical features of these patients in relation to the associated mutations.