Novel GUCY2D Gene Mutations in Japanese Male Twins with Leber Congenital Amaurosis

Ocular genetics in the Japanese population

In today's globalized society, ophthalmologists can examine people of different ethnicities regardless of where they live. The frequency of disease-causing genes varies according to a patient's ethnic background. We explain genetic findings for Japanese patients with inherited eye diseases. Ocular genetics has made great advances over the past 30 years. For example, detecting mutations at nucleotide position 11778 in mitochondrial DNA was useful in the genetic diagnosis of Leber's hereditary optic neuropathy (LHON). I evaluated the genotype-phenotype relationship in cases of corneal dystrophy and inherited retinal dystrophy (IRD). I identified the entire exon sequence of the eyes shut homolog (EYS) gene in patients with autosomal recessive retinitis pigmentosa (RP). EYS gene mutations are the most frequent cause of autosomal recessive RP. RPGRIP1 may be a common causative gene with early-onset severe retinal dystrophy, including Leber congenital amaurosis. However, some genes have complex structures that are difficult to analyze, including the OPN1LW/OPN1MW gene cluster in blue cone monochromacy and the IKBKG/NEMO genes in incontinentia pigmenti. This review will also present two cases with uniparental disomy, a case of IRD with double mutations, and a case with RP complicated with LHON-like neuropathy. Precise understanding of the effects of genetic variants may reveal differences in the clinical characteristics of patients with the same variant. When starting genome medicine, accurately diagnosing the patient, making accurate prediction, determining the genetic pattern, and providing genetic counseling are important. Above all, that both the doctors and patients understand genetic diseases correctly is important.

Phenotypic characterization of autosomal dominant progressive cone dystrophies associated with a heterozygous variant c.2512C>T of GUCY2D gene in a large kindred

PURPOSE

In this study, we described a large family presenting different manifestations of cone dystrophy at different ages associated with GUCY2D gene mutation.

METHOD

Sixty-three individuals of a single kindred, including 23 affected with cone dystrophies, were recruited and received ocular examinations, including best corrected visual acuity, intraocular pressure, slit-lamp biomicroscopy, color fundus photograph (CFP), fundus autofluorescence, optical coherence tomography, fluorescence fundus angiography, color vision testing, full-field electroretinography, and electro-oculogram. Whole exome sequencing (WES) and Sanger sequencing were performed for underlying mutations associated with cone dystrophy.

RESULT

There were 23 affected family members. Clinical analysis showed that the proband and other patients had impaired visual acuity ranging from 20/800 to 20/50 with impaired color vision. Fundus photograph showed retinal pigment epithelium (RPE) granular abnormalities with depressed macular reflex in young patients and macular or retinochoriodal atrophy in older patients. OCT examination confirmed the reduced outer retinal thickness or inner retinal thickness, absence of the ellipsoid zone (EZ) and retinal atrophy to varying degrees. Electroretinography revealed a reduced cone response combined with a relatively maintained rod response. WES and Sanger sequencing revealed a heterozygous variant c.2512C>T in the GUCY2D gene of the affected family members.

CONCLUSIONS

We reported cone dystrophy in 23 affected individuals in a five-generation family and demonstrated different macular abnormalities in OCT scans and CFP at different ages. The multimodal ocular records in our study provide physicians and ophthalmologists with a better understanding of cone dystrophy associated with GUCY2D mutation.

Clinical and Genetic Characteristics of 15 Affected Patients From 12 Japanese Families with GUCY2D-Associated Retinal Disorder

Purpose

To determine the clinical and genetic characteristics of patients with GUCY2D-associated retinal disorder (GUCY2D-RD).

Methods

Fifteen patients from 12 families with inherited retinal disorder (IRD) and harboring GUCY2D variants were ascertained from 730 Japanese families with IRD. Comprehensive ophthalmological examinations, including visual acuity (VA) measurement, retinal imaging, and electrophysiological assessment were performed to classify patients into three phenotype subgroups; macular dystrophy (MD), cone-rod dystrophy (CORD), and Leber congenital amaurosis (LCA). In silico analysis was performed for the detected variants, and the molecularly confirmed inheritance pattern was determined (autosomal dominant/recessive [AD/AR]).

Results

The median age of onset/examination was 22.0/38.0 years (ranges, 0-55 and 1-73) with a median VA of 0.80/0.70 LogMAR units (ranges, 0.00-1.52 and 0.10-1.52) in the right/left eye, respectively. Macular atrophy was identified in seven patients (46.7%), and two had diffuse fundus disturbance (13.3%), and six had an essentially normal fundus (40.0%). There were 11 patients with generalized cone-rod dysfunction (78.6%), two with entire functional loss (14.3%), and one with confined macular dysfunction (7.1%). There were nine families with ADCORD, one with ARCORD, one with ADMD, and one with ARLCA. Ten GUCY2D variants were identified, including four novel variants (p.Val56GlyfsTer262, p.Met246Ile, p.Arg761Trp, p.Glu874Lys).

Conclusions

This large cohort study delineates the disease spectrum of GUCY2D-RD. Diverse clinical presentations with various severities of ADCORD and the early-onset severe phenotype of ARLCA are illustrated. A relatively lower prevalence of GUCY2D-RD for ADCORD and ARLCA in the Japanese population was revealed.

Translational Relevance

The obtained data help to monitor and counsel patients, especially in East Asia, as well as to design future therapeutic approaches.

GUCY2D-Associated Leber Congenital Amaurosis: A Retrospective Natural History Study in Preparation for Trials of Novel Therapies

PURPOSE

To describe the natural history of Leber congenital amaurosis (LCA) associated with GUCY2D variants (GUCY2D-LCA) in a cohort of children and adults, in preparation for trials of novel therapies.

DESIGN

Retrospective case series.

METHODS

Participants: Patients with GUCY2D-LCA at a single referral center.

PROCEDURES

Review of clinical notes, retinal imaging including fundus autofluorescence (FAF) and optical coherence tomography (OCT), electroretinography (ERG), and molecular genetic testing.

MAIN OUTCOME MEASURES

Demographic data, symptoms at presentation, visual acuity, evidence of progression, OCT and FAF findings, ERG assessment, and molecular genetics.

RESULTS

Twenty-one subjects with GUCY2D-LCA were included, with a mean follow-up ± standard deviation (SD) of 10 ± 11.85 years. Marked reduction in visual acuity (VA) and nystagmus was documented in all patients within the first 3 years of life. Fifty-seven percent (n = 12) exhibited photophobia and 38% (n = 8) had nyctalopia. VA was worse than hand motion in 71% of the patients (n = 15). Longitudinal assessment of VA showed stability in all patients, except 1 patient who experienced deterioration over a follow-up of 44 years. Hyperopia was reported in 13 of the 17 subjects (71%) with available refraction data. Eighteen subjects had either normal fundus appearance (n = 14) or a blond fundus (n = 3), while only 4 of the eldest subjects had mild retinal pigment epithelium (RPE) atrophy (mean, 49 years; range 40-54 years). OCT data were available for 11 subjects and 4 different grades of ellipsoid zone (EZ) integrity were identified: (1) continuous/intact EZ (n = 6), (2) focally disrupted EZ (n = 2), (3) focally disrupted with RPE changes (n = 2), and (4) diffuse EZ disruption with RPE changes (n = 1). All examined subjects had stable OCT findings over the long follow-up period. Full-field ERGs showed evidence of a severe cone-rod dystrophy in 5 of 6 patients and undetectable ERGs in 1 subject. Novel genotype-phenotype correlations are also reported.

CONCLUSION

GUCY2D-LCA is a severe early-onset retinal dystrophy associated with very poor VA from birth. Despite the severely affected photoreceptor function, the relatively preserved photoreceptor structure based on EZ integrity until late in the disease in the majority of subjects suggests a wide therapeutic window for gene therapy trials.

Retinal structure in Leber's congenital amaurosis caused by RPGRIP1 mutations

This study aimed to evaluate retinal structure in the early stage of Leber’s congenital amaurosis (LCA) caused by RPGRIP1 mutations. Four patients from two families were included. Case 1 was a 13-year-old girl, cases 2 and 3 were 7-year-old monozygotic twin brothers of case 1, and case 4 was a 17-year-old boy. Comprehensive ophthalmic examinations were performed, including visual acuity measurements, perimetry, electroretinography (ERG), and optical coherence tomography (OCT). To identify potential pathogenic mutations, 74 genes known to cause retinitis pigmentosa or LCA were assessed using targeted next-generation sequencing. OCT showed photoreceptor outer nuclear layer (ONL) thinning in all patients. The lamellar structure was retained in all patients, whereas the ellipsoid zone was extinguished in cases 1, 2, and 3. In case 4, the ellipsoid zone was maintained at 9 years of age but became blurred at 17 years of age. In case 1, OCT indicated slight photoreceptor ONL thinning during the period between 7 and 11 years of age. Mutation analysis revealed RPGRIP1 mutations as the cause for autosomal recessive LCA in all patients. Photoreceptor ONL on OCT is relatively well preserved in the early stage of LCA caused by RPGRIP1 mutations.

Researchers in Japan have characterized the early stages of the inherited retinal disease Leber’s congenital amaurosis (LCA), raising hope that gene therapy could help before the disease progresses too far. LCA results in early-onset blindness or severe visual impairment and has been linked with several genes, including RPGRIP1. Daisuke Miyamichi from Hamamatsu University School of Medicine, Japan, and coworkers conducted ophthalamic tests on four young patients with RPGRIP1 mutations. In all four cases, they found thinning of the photoreceptor outer nuclear layer, a layer of the retina. The outer nuclear layer progressively thinned in consecutive samples taken from the same patient at different ages, and was better retained in the younger patients. Taken together, these findings suggest that gene therapy to correct RPGRIP1 mutations could be effective if carried out in early childhood.

X-linked Retinitis Pigmentosa in Japan: Clinical and Genetic Findings in Male Patients and Female Carriers

X-linked retinitis pigmentosa (XLRP) is a type of severe retinal dystrophy, and female carriers of XLRP demonstrate markedly variable clinical severity. In this study, we aimed to elucidate the clinical findings of male patients with and female carriers of XLRP in a Japanese cohort and demonstrate the genetic contribution. Twelve unrelated families (13 male patients, 15 female carriers) harboring pathogenic mutations in RPGR or RP2 were included, and comprehensive ophthalmic examinations were performed. To identify potential pathogenic mutations, targeted next-generation sequencing was employed. Consequently, we identified 11 pathogenic mutations, of which five were novel. Six and five mutations were detected in RPGR and RP2, respectively. Only one mutation was detected in ORF15. Affected male patients with RP2 mutations tended to have lower visual function than those with RPGR mutations. Female carriers demonstrated varying visual acuities and visual fields. Among the female carriers, 92% had electroretinographical abnormalities and 63% had a radial autofluorescent pattern, and the carriers who had higher myopia showed worse visual acuity and more severe retinal degeneration. Our results expand the knowledge of the clinical phenotypes of male patients with and female carriers of XLRP and suggest the possibility that RP2 mutations are relatively highly prevalent in Japan.

Molecular Diagnosis of 34 Japanese Families with Leber Congenital Amaurosis Using Targeted Next Generation Sequencing

Leber congenital amaurosis (LCA) is a genetically and clinically heterogeneous disease, and represents the most severe form of inherited retinal dystrophy (IRD). The present study reports the mutation spectra and frequency of known LCA and IRD-associated genes in 34 Japanese families with LCA (including three families that were previously reported). A total of 74 LCA- and IRD-associated genes were analysed via targeted-next generation sequencing (TS), while recently discovered LCA-associated genes, as well as known variants not able to be screened using this approach, were evaluated via additional Sanger sequencing, long-range polymerase chain reaction, and/or copy number variation analyses. The results of these analyses revealed 30 potential pathogenic variants in 12 (nine LCA-associated and three other IRD-associated) genes among 19 of the 34 analysed families. The most frequently mutated genes were CRB1, NMNAT1, and RPGRIP1. The results also showed the mutation spectra and frequencies identified in the analysed Japanese population to be distinctly different from those previously identified for other ethnic backgrounds. Finally, the present study, which is the first to conduct a NGS-based molecular diagnosis of a large Japanese LCA cohort, achieved a detection rate of approximately 56%, indicating that TS is a valuable method for molecular diagnosis of LCA cases in the Japanese population.

Long-term clinical course of 2 Japanese patients with PRPF31-related retinitis pigmentosa

PURPOSE

To assess the long-term clinical course of 2 patients with PRPF31-related retinitis pigmentosa (RP).

PATIENTS AND METHODS

We clinically examined 2 unrelated patients with RP and collected peripheral blood samples from them. Ophthalmic examinations, including best-corrected visual acuity measurements, Goldmann perimetry, full-field electroretinography, fundus autofluorescence imaging, and optical coherence tomography, were also performed. The visual acuity and visual field were continuously monitored. To identify the causative mutations, 74 genes known to cause RP or Leber congenital amaurosis were examined via targeted next-generation sequencing.

RESULTS

The clinical courses of both patients were similar. The onset of nyctalopia occurred in the first decade. Fundus examination showed typical RP. Although the patients' visual acuity was relatively preserved even into the fourth decade, the visual field area exhibited rapid deterioration in the mid-teens, with severe concentric constriction in the third decade. Mutation analysis revealed PRPF31 mutations as the cause for autosomal dominant RP in both patients.

CONCLUSIONS

To the best of our knowledge, few reports of long-term observations pertaining to patients with PRPF31-related RP have been published. The findings reported herein, especially those relating to the progressive degeneration of the visual field, may ultimately play a role in the provision of high-quality counseling for patients with this condition.

Visual Outcomes in Japanese Patients with Retinitis Pigmentosa and Usher Syndrome Caused by USH2A Mutations

PURPOSE

EYS and USH2A are the most common causative genes for retinitis pigmentosa (RP) in Japan. We determined the clinical outcomes for USH2A-related non-syndromic RP or Usher syndrome type II (USH2).

METHODS

Two non-syndromic RP and 11 USH2 patients with previously identified USH2A mutations were included. Their complete history and medical records were collected using standard procedures. Visual fields and acuity were compared with those of patients with EYS mutations. Clinical analyses were based on ophthalmic and otolaryngologic examinations.

RESULTS

In all patients, the fundus displayed changes typical of RP. Most patients showed relatively well-preserved visual acuity in their thirties or forties, with rapid deterioration in their fifties. Concentric constriction started in the twenties or thirties, and no effective residual visual field was observed after the fifties.

CONCLUSIONS

The visual outcome for non-syndromic RP or USH2 patients with USH2A mutations is consistent with that for RP patients with EYS mutations.

Defining Outcomes for Clinical Trials of Leber Congenital Amaurosis Caused by GUCY2D Mutations

PURPOSE

To determine outcome measures for a clinical trial of Leber congenital amaurosis (LCA) associated with mutations in the GUCY2D gene.

DESIGN

Retrospective observational case series.

METHODS

Twenty-eight patients with GUCY2D-LCA (aged 2-59 years) were studied clinically and with chromatic full-field sensitivity testing (FST), optical coherence tomography (OCT), pupillometry, and the NEI Visual Function Questionnaire (VFQ).

RESULTS

FST permitted quantitation of cone and rod sensitivity in these patients with severe visual impairment. For most patients, the degree of rod and cone sensitivity losses showed a relationship, thereby providing an opportunity to divide patients into cohorts by severity of rod and cone dysfunction. OCT analyses indicated that retinal structure could be used not only as an objective safety measure but also as an exploratory efficacy outcome. A foveal bulge was not present in 67% of patients. The intensity of inner segment/outer segment (ellipsoid zone line) reflectivity was reduced significantly at the fovea and in the rod-dense superior retina. Based on OCT and FST parameters, most patients had dissociation of structure and function. Abnormal pupillometry sensitivity in the majority of GUCY2D-LCA patients provided another objective efficacy outcome. NEI VFQ scores showed a similar range of findings to those of other severe retinal diseases.

CONCLUSION

Conventional outcome measures, such as visual acuity and the NEI VFQ, will need to be complemented by methods more specific to this GUCY2D-LCA population. Any therapeutic strategy should determine if there is an effect on rod as well as cone function and structure. FST provides a photoreceptor-based subjective outcome; and OCT in 2 retinal regions, fovea and superior retina, can assess photoreceptor structure. A change in the relationship of structure and function away from baseline becomes evidence of efficacy.