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.

Genetic and Clinical Features of ABCA4-Associated Retinopathy in a Japanese Nationwide Cohort.

PURPOSE: To clarify the genetic and clinical features of Japanese patients with ABCA4-associated retinopathy. DESIGN: Retrospective, multicenter cohort study. METHODS: Patients with retinal degeneration and biallelic ABCA4 variants were recruited from 13 different hospitals. Whole exome sequencing analysis was used for genetic testing. Comprehensive ophthalmic examinations were performed on matched patients. The primary outcome measure was identifying multimodal retinal imaging findings associated with disease progression. RESULTS: This study included 63 patients: 19 with missense/missense, 23 with missense/truncation, and 21 with truncation/truncation genotypes. In total, 62 variants were identified, including 29 novel variants. Six patients had a mild phenotype characterized by foveal-sparing or preserved foveal structure, including 4 with missense/missense and 2 with missense/truncation genotypes. The p.Arg212His variant was the most frequent in patients with mild phenotypes (4/12 alleles). Clinical findings showed a disease duration-dependent worsening of the phenotypic stage. Patients with the truncation/truncation genotype exhibited rapid retinal degeneration within a few years and definite fundus autofluorescence imaging patterns, including hyper autofluorescence at the macula and few or no flecks. CONCLUSIONS: Our results indicate that missense/missense or missense/truncation genotypes, including the p.Arg212His variant, are associated with a relatively mild phenotype. In contrast, the truncation/truncation genotype causes rapid and severe retinal degeneration in Japanese patients with ABCA4-associated retinopathy. These data are vital in predicting patient prognosis, guiding genetic counseling, and stratifying patients for future clinical trials.

The Structural Abnormalities Are Deeply Involved in the Cause of RPGRIP1-Related Retinal Dystrophy in Japanese Patients.

Leber congenital amaurosis (LCA) is the most severe form of inherited retinal dystrophy. RPGRIP1-related LCA accounts for 5-6% of LCA. We performed whole-exome sequencing and whole-genome sequencing (WGS) on 29 patients with clinically suspected LCA and examined ophthalmic findings in patients with biallelic pathogenic variants of RPGRIP1. In addition to five previously reported cases, we identified five cases from four families with compound heterozygous RPGRIP1 variants using WGS. Five patients had null variants comprising frameshift variants, an Alu insertion, and microdeletions. A previously reported 1339 bp deletion involving exon 18 was found in four cases, and the deletion was relatively prevalent in the Japanese population (allele frequency: 0.002). Microdeletions involving exon 1 were detected in four cases. In patients with RPGRIP1 variants, visual acuity remained low, ranging from light perception to 0.2, and showed no correlation with age. In optical coherence tomography images, the ellipsoid zone (EZ) length decreased with age in all but one case of unimpaired EZ. The retinal structure was relatively preserved in all cases; however, there were cases with great differences in visual function compared to their siblings and a 56-year-old patient who still had a faint EZ line. Structural abnormalities may be important genetic causes of RPGRIP1-related retinal dystrophy in Japanese patients, and WGS was useful for detecting them.

A pediatric case of congenital stromal corneal dystrophy caused by the novel variant c.953del of the DCN gene.

We report a 1-year-old girl with congenital stromal corneal dystrophy confirmed by genetic analysis. The ocular phenotype included diffuse opacity over the corneal stroma bilaterally. We performed a genetic analysis to provide counseling to the parents regarding the recurrence rate. Whole exome sequencing was performed on her and her parents, and a novel de novo variant, NM_001920.5: c.953del, p.(Asn318Thrfs*10), in the DCN gene was identified in the patient.

A case of siblings with juvenile retinitis pigmentosa associated with NEK1 gene variants.

BACKGROUND: Axial spondylometaphyseal dysplasia(axial SMD) is associated with early-onset retinal dystrophy and various skeletal dysplasias of varying severity. NEK1 is the causative gene for short rib polydactyly syndrome and axial SMD. Here, we report a case of siblings with juvenile retinitis pigmentosa (RP) and NEK1 variants not associated with systemic disorders. MATERIALS AND METHODS: The patients were a 7-year-old-girl and a 9-year-old boy with RP, who were followed for 9 years. Whole exome sequencing (WES) was performed on the siblings and their parents, who were not consanguineous. RESULTS: The corrected visual acuity of the girl and the boy at first visit was binocular 20/63 and 20/100 OD and 20/63 OS, respectively. The siblings had narrowing of retinal blood vessels and retinal pigment epithelium atrophy in the fundus and showed an extinguished pattern in electroretinogram. On optical coherence tomography, there was a mottled ellipsoid band with progressive loss in the outer macular, the edges of which corresponded to the ring of hyperautofluorescence on fundus autofluorescence imaging. The siblings showed progressive visual field constriction. Radiological examination did not reveal any skeletal abnormalities. We identified two rare heterozygous NEK1 variants in the patients: c.240 G>A; p.(M80I) and c.634_639dup;p.(V212_L213dup). Heterozygous variants were recognized in the father and mother, respectively. According to the guidelines of the American College of Medical Genetics and Genomics, both variants were classified as likely pathogenic. CONCLUSION: This is the first report of RP patients with NEK1 variants not associated with skeletal abnormalities.

Maternal Uniparental Isodisomy of Chromosome 4 and 8 in Patients with Retinal Dystrophy: SRD5A3-Congenital Disorders of Glycosylation and RP1-Related Retinitis Pigmentosa.

PURPOSE: Uniparental disomy (UPD) is a rare chromosomal abnormality. We performed whole-exosome sequencing (WES) in cases of early-onset retinal dystrophy and identified two cases likely caused by UPD. Herein, we report these two cases and attempt to clarify the clinical picture of retinal dystrophies caused by UPD. METHODS: WES analysis was performed for two patients and their parents, who were not consanguineous. Functional analysis was performed in cases suspected of congenital disorders of glycosylation (CDG). We obtained clinical case data and reviewed the literature. RESULTS: In case 1, a novel c.57G>C, p.(Trp19Cys) variant in SRD5A3 was detected homozygously. Genetic analysis suggested a maternal UPD on chromosome 4, and functional analysis confirmed CDG. Clinical findings showed early-onset retinal dystrophy, intellectual disability, and epilepsy. In case 2, an Alu insertion (c.4052_4053ins328, p.[Tyr1352Alafs]) in RP1 was detected homozygously. Maternal UPD on chromosome 8 was suspected. The clinical picture was consistent with RP1-related retinitis pigmentosa. Although the clinical features of retinal dystrophy by UPD may vary, most cases present with childhood onset. CONCLUSIONS: There have been limited reports of retinal dystrophy caused by UPD, suggesting that it is rare. Genetic counseling may be encouraged in pediatric cases of retinal dystrophy.