Mizuo-Nakamura phenomenon in X-linked retinoschisis.

Purpose: To determine whether the Mizuo-Nakamura phenomenon, which is an important diagnostic sign of Oguchi's disease, also occurs in patients with genetically proven X-linked retinoschisis (XLRS). Methods: We examined three patients with a clinical and genetic diagnosis of XLRS and one patient who was clinically diagnosed with Oguchi's disease, with an emphasis on the Mizuo-Nakamura phenomenon. We obtained color fundus photographs, especially in the fully dark-adapted state, using the non-mydriatic mode on a digital retinal camera and infrared observation monitor to avoid the bleaching effects caused by the viewing light, which alters the fundus color in a short time. Results: The Mizuo-Nakamura phenomenon was observed in all patients with molecularly proven XLRS, similar to that in the patient with Oguchi's disease. The sets of photographs were obtained in the light- and dark-adapted states using our newly devised techniques needed to witness the Mizuo-Nakamura phenomenon. Conclusions and Importance: The Mizuo-Nakamura phenomenon was identified in three patients with genetically proven XLRS. To the best of our knowledge, this study provided the first genetic evidence of the Mizuo-Nakamura phenomenon in a patient with molecularly proven XLRS without the causative genetic abnormalities for Oguchi's disease. Our findings suggest that XLRS is responsible for the Mizuo-Nakamura phenomenon and its presence in XLRS is not a rare exception but may be a consistent manifestation of XLRS.

Retinitis Pigmentosa with EYS Mutations Is the Most Prevalent Inherited Retinal Dystrophy in Japanese Populations.

The aim of this study was to gain information about disease prevalence and to identify the responsible genes for inherited retinal dystrophies (IRD) in Japanese populations. Clinical and molecular evaluations were performed on 349 patients with IRD. For segregation analyses, 63 of their family members were employed. Bioinformatics data from 1,208 Japanese individuals were used as controls. Molecular diagnosis was obtained by direct sequencing in a stepwise fashion utilizing one or two panels of 15 and 27 genes for retinitis pigmentosa patients. If a specific clinical diagnosis was suspected, direct sequencing of disease-specific genes, that is, ABCA4 for Stargardt disease, was conducted. Limited availability of intrafamily information and decreasing family size hampered identifying inherited patterns. Differential disease profiles with lower prevalence of Stargardt disease from European and North American populations were obtained. We found 205 sequence variants in 159 of 349 probands with an identification rate of 45.6%. This study found 43 novel sequence variants. In silico analysis suggests that 20 of 25 novel missense variants are pathogenic. EYS mutations had the highest prevalence at 23.5%. c.4957_4958insA and c.8868C>A were the two major EYS mutations identified in this cohort. EYS mutations are the most prevalent among Japanese patients with IRD.

Constructive rescue of TFIIH instability by an alternative isoform of XPD derived from a mutated XPD allele in mild but not severe XP-D/CS.

Mutations in XPD cause xeroderma pigmentosum (XP), XP and Cockayne syndrome (CS) crossover syndrome (XP/CS), trichothiodystrophy and cerebro-oculo-facio-skeletal syndrome (COFS). COFS represents the most severe end of the CS spectrum. This study reports two Japanese patients, COFS-05-135 and COFS-Chiba1, who died at ages of <1 year and exhibited typical COFS manifestations caused by XPD mutations p.[I619del];[R666W] and p.[G47R];[I619del], respectively. Two other cases of severe XP-D/CS (XP group D/CS), XP1JI (p.[G47R];[0]) and XPCS1PV (p.[R666W];[0]), died at ages <2 years. On the other hand, two cases of mild XP-D/CS, XP1NE (p.[G47R];[L461V;V716_R730del]) and XPCS118LV (p.[L461V;V716_R730del];[R666W]), lived beyond 37 years of age. p.I619Del and p.[L461V;V716_R730del] are functionally null; therefore, despite the differences in clinical manifestations, the functional protein in all of these patients was either p.G47R or p.R666W. To resolve the discrepancies in these XPD genotype-phenotype relationships, the p.[L461V;V716_R730del] allele was analyzed and we found that p.[L461V;A717G] was expressed from the same allele as p.[L461V;V716_R730del] by authentic splicing. Additionally, p.[L461V;A717G] could partially rescue the loss of XPD function, resulting in the milder manifestations observed in XP1NE and XPCS118LV.

The first USH2A mutation analysis of Japanese autosomal recessive retinitis pigmentosa patients: a totally different mutation profile with the lack of frequent mutations found in Caucasian patients.

Retinitis pigmentosa (RP) is a highly heterogeneous genetic disease. The USH2A gene, which accounts for approximately 74-90% of Usher syndrome type 2 (USH2) cases, is also one of the major autosomal recessive RP (arRP) causative genes among Caucasian populations. To identify disease-causing USH2A gene mutations in Japanese RP patients, all 73 exons were screened for mutations by direct sequencing. In total, 100 unrelated Japanese RP patients with no systemic manifestations were identified, excluding families with obvious autosomal dominant inheritance. Of these 100 patients, 82 were included in this present study after 18 RP patients with very likely pathogenic EYS (eyes shut homolog) mutations were excluded. The mutation analysis of the USH2A revealed five very likely pathogenic mutations in four patients. A patient had only one very likely pathogenic mutation and the others had two of them. Caucasian frequent mutations p.C759F in arRP and p.E767fs in USH2 were not found. All the four patients exhibited typical clinical features of RP. The observed prevalence of USH2A gene mutations was approximately 4% among Japanese arRP patients, and the profile of the USH2A gene mutations differed largely between Japanese patients and previously reported Caucasian populations.

A point mutation in Semaphorin 4A associates with defective endosomal sorting and causes retinal degeneration.

Semaphorin 4A (Sema4A) has an essential role in photoreceptor survival. In humans, mutations in Sema4A are thought to contribute to retinal degenerative diseases. Here we generate a series of knock-in mouse lines with corresponding mutations (D345H, F350C or R713Q) in the Sema4A gene and find that Sema4A(F350C) causes retinal degeneration phenotypes. The F350C mutation results in abnormal localization of the Sema4A protein, leading to impaired endosomal sorting of molecules indispensable for photoreceptor survival. Additionally, protein structural modelling reveals that the side chain of the 350th amino acid is critical to retain the proper protein conformation. Furthermore, Sema4A gene transfer successfully prevents photoreceptor degeneration in Sema4A(F350C/F350C) and Sema4A(-/-) mice. Thus, our findings not only indicate the importance of the Sema4A protein conformation in human and mouse retina homeostasis but also identify a novel therapeutic target for retinal degenerative diseases.

Mutations in UVSSA cause UV-sensitive syndrome and destabilize ERCC6 in transcription-coupled DNA repair.

UV-sensitive syndrome (UV(S)S) is an autosomal recessive disorder characterized by photosensitivity and deficiency in transcription-coupled repair (TCR), a subpathway of nucleotide-excision repair that rapidly removes transcription-blocking DNA damage. Cockayne syndrome is a related disorder with defective TCR and consists of two complementation groups, Cockayne syndrome (CS)-A and CS-B, which are caused by mutations in ERCC8 (CSA) and ERCC6 (CSB), respectively. UV(S)S comprises three groups, UV(S)S/CS-A, UV(S)S/CS-B and UV(S)S-A, caused by mutations in ERCC8, ERCC6 and an unidentified gene, respectively. Here, we report the cloning of the gene mutated in UV(S)S-A by microcell-mediated chromosome transfer. The predicted human gene UVSSA (formerly known as KIAA1530)(7) corrects defective TCR in UV(S)S-A cells. We identify three nonsense and frameshift UVSSA mutations in individuals with UV(S)S-A, indicating that UVSSA is the causative gene for this syndrome. The UVSSA protein forms a complex with USP7 (ref. 8), stabilizes ERCC6 and restores the hypophosphorylated form of RNA polymerase II after UV irradiation.

Two novel mutations in the EYS gene are possible major causes of autosomal recessive retinitis pigmentosa in the Japanese population.

Retinitis pigmentosa (RP) is a highly heterogeneous genetic disease including autosomal recessive (ar), autosomal dominant (ad), and X-linked inheritance. Recently, arRP has been associated with mutations in EYS (Eyes shut homolog), which is a major causative gene for this disease. This study was conducted to determine the spectrum and frequency of EYS mutations in 100 Japanese arRP patients. To determine the prevalence of EYS mutations, all EYS exons were screened for mutations by polymerase chain reaction amplification, and sequence analysis was performed. We detected 67 sequence alterations in EYS, of which 21 were novel. Of these, 7 were very likely pathogenic mutations, 6 were possible pathogenic mutations, and 54 were predicted non-pathogenic sequence alterations. The minimum observed prevalence of distinct EYS mutations in our study was 18% (18/100, comprising 9 patients with 2 very likely pathogenic mutations and the remaining 9 with only one such mutation). Among these mutations, 2 novel truncating mutations, c.4957_4958insA (p.S1653KfsX2) and c.8868C>A (p.Y2956X), were identified in 16 patients and accounted for 57.1% (20/35 alleles) of the mutated alleles. Although these 2 truncating mutations were not detected in Japanese patients with adRP or Leber's congenital amaurosis, we detected them in Korean arRP patients. Similar to Japanese arRP results, the c.4957_4958insA mutation was more frequently detected than the c.8868C>A mutation. The 18% estimated prevalence of very likely pathogenic mutations in our study suggests a major involvement of EYS in the pathogenesis of arRP in the Japanese population. Mutation spectrum of EYS in 100 Japanese patients, including 13 distinct very likely and possible pathogenic mutations, was largely different from the previously reported spectrum in patients from non-Asian populations. Screening for c.4957_4958insA and c.8868C>A mutations in the EYS gene may therefore be very effective for the genetic testing and counseling of RP patients in Japan.

[A case of Oguchi disease with disappearance of golden tapetal-like fundus reflex after vitreous resection].

BACKGROUND: Oguchi disease is a form of congenital stationary night-blindness characterized by a golden tapetal fundus reflex. This reflex is known to disappear in the dark-adapted state ("Mizuo-Nakamura phenomenon"). The origin of the reflex is not clear. We report a case of Oguchi disease with the disappearance of the golden tapetal reflex after vitreous resection. CASE: An 80-year-old man was referred for rhegmatogenous retinal detachment of the left eye. Golden tapetal reflex was observed in both eyes. Negative b-wave in the electroretinogram and mutation in the SAG gene indicated Oguchi disease. Pars plana vitrectomy and posterior hyaloid membrane peeling were performed. The tapetal reflex in the all regions of the fundus in the operated eye disappeared after the retina was reattached. The reflex partially recovered 2 years after the operation. CONCLUSION: It is suggested that the change in vitreo-retinal interface after a vitreous operation leads to the disappearance of the reflex. This report presents a hypothesis on the origin of the golden tapetal reflex in Oguchi disease.

Oguchi disease masked by retinitis pigmentosa.

The purpose of this study was to report a patient with Oguchi disease whose ophthalmological characteristics were masked by retinitis pigmentosa (RP). The method used in this study was case report. A 53-year-old man had a progressive decrease in his visual acuity and was diagnosed with RP because of night blindness, fundoscopic findings, ring scotoma, and extinguished single-flash electroretinograms (ERGs). However, a faint golden-yellowish reflex of the retina prompted us to make a more detailed examination of the fundus after a long period of dark adaptation, ERGs, and genetic analysis. Examinations showed the Mizuo-Nakamura phenomenon, relative intact photopic ERGs, and a SAG mutation, and the patient was diagnosed with RP associated with Oguchi disease. When RP accompanies Oguchi disease, the clinical characteristics of Oguchi disease might be masked. In such a situation, the correct diagnosis is difficult. However, careful analysis of clinical findings will suggest Oguchi disease, which can be confirmed by molecular genetics.

Use of lectins to enrich mouse ES-derived retinal progenitor cells for the purpose of transplantation therapy.

Using the mouse ES cell line with green fluorescent protein knocked-in at the Rx locus (Rx-KI ES cell), we previously showed that photoreceptors can be efficiently obtained in defined culture conditions by enriching Rx-positive retinal progenitor cells. We aimed to explore a protocol applicable for non-Rx-labeled stem cell lines for subsequent enrichment of retinal photoreceptor precursors for transplantation. The Rx-KI ES cell line was differentiated according to the serum-free suspension conditions with serum-free suspension/Dkk1/LeftyA/serum/activin method (SFEB/DLFA) described previously. Enrichment efficacy by negative selection was compared among 20 different lectins and the lectin combination that effectively enriched the Rx-positive cells by selecting the lectin low-binding population was determined. Subsequent differentiation efficiency to photoreceptor precursors and the contamination of Nanog or Oct3/4(+) cells in the culture were evaluated between the cell cultures using negative selection with lectins and Rx positive selection. The effect of cytarabine (Ara-C) for minimizing the contamination of undifferentiated cells after the selection was also studied. The combination of the lectins, wheat germ agglutinin (WGA), and Erythrina crista-galli agglutinin (ECA) enabled us to enrich the Rx-positive population by approximately twice the original Rx percentage. The selection also minimized the percentage of Oct3/4(+) cells. The lectin-selected cells produced a comparable percentage of Crx/rhodopsin-positive colonies with Rx-positive selection and were differentiated into photoreceptors. The Ara-C treatment on differentiating days 24-26 decreased Nanog and Oct3/4 expression in subsequent cultures. Enrichment of Rx-positive cells using WGA and ECA was comparable to Rx-positive selection, and the method could be applied to achieve efficient photoreceptor differentiation from other ES or iPS cell lines in which the Rx gene is not marked.

Allelic copy number variation in FSCN2 detected using allele-specific genotyping and multiplex real-time PCRs.

PURPOSE: Allelic copy number variation (CNV) may alter the functional effects of a heterozygous mutation. The underlying mechanisms and their roles in hereditary diseases, however, are largely unknown. In the present study an FSCN2 mutation was examined that has been reported, not only in patients with retinitis pigmentosa (RP), but also in the normal population. METHODS: Experiments were performed to investigate the gene and allele copy numbers of FSCN2 in patients with RP who have the c.72delG mutation as well as healthy subjects with or without the mutation. A real-time PCR-based genotyping approach was established that used a real-time PCR assay to qualify the copy numbers of both the wild-type and mutant alleles of the FSCN2 gene. RESULTS: Three patients with RP and three normal subjects had an equal ratio of the alleles. Of interest, another patient had an asymmetric allele ratio (4:1) of the copy number of the wild-type allele, compared with that of the mutant allele. These findings were further verified using quantitative assays. An allele-specific methylation assay demonstrated a random methylation pattern in the FSCN2 gene. CONCLUSIONS: The copy numbers of the FSNC2 gene and of each allele in the mutant samples were quantified. The findings excluded the possibility that allelic CNV was associated with RP, suggesting that the c.72delG variant is not the primary cause of RP. It is not likely that the FSCN2 gene is imprinted differentially. The real-time PCR-based genotyping method developed in this study is useful for investigations of allelic asymmetries within genomic regions with CNVs.

XPG stabilizes TFIIH, allowing transactivation of nuclear receptors: implications for Cockayne syndrome in XP-G/CS patients.

Mutations in the human XPG gene give rise to an inherited photosensitive disorder, xeroderma pigmentosum (XP) associated with Cockayne syndrome (XP-G/CS). The clinical features of CS in XP-G/CS patients are difficult to explain on the basis of a defect in nucleotide excision repair (NER). We found that XPG forms a stable complex with TFIIH, which is active in transcription and NER. Mutations in XPG found in XP-G/CS patient cells that prevent the association with TFIIH also resulted in the dissociation of CAK and XPD from the core TFIIH. As a consequence, the phosphorylation and transactivation of nuclear receptors were disturbed in XP-G/CS as well as xpg(-/-) MEF cells and could be restored by expression of wild-type XPG. These results provide an insight into the role of XPG in the stabilization of TFIIH and the regulation of gene expression and provide an explanation of some of the clinical features of XP-G/CS.