A novel homozygous GRK1 mutation (P391H) in 2 siblings with Oguchi disease with markedly reduced cone responses.

PURPOSE: The only mutations reported to date in Japanese patients with Oguchi disease, a rare form of stationary night blindness with autosomal recessive transmission, have been in the SAG (arrestin) gene. The objective of this study was to describe the ophthalmic features and a novel mutation in the GRK1 (rhodopsin kinase) gene in 2 Japanese patients with Oguchi disease. DESIGN: Molecular genetic and observational case study. PARTICIPANTS: A consanguineous family including 2 siblings with Oguchi disease (a 35-year-old man and a 31-year-old woman). METHODS: Best-corrected visual acuity (BCVA), fundus examinations, Goldmann perimetry, color vision tests, and full-field electroretinograms (ERGs) were evaluated. Mutation screening of the SAG and GRK1 genes was performed with polymerase chain reaction amplification and direct sequencing. MAIN OUTCOME MEASURES: Mutations in the GRK1 gene, BCVA, color vision, fundus photographs, visual fields, and ERG findings. RESULTS: Molecular analysis revealed a novel homozygous missense mutation (p.P391H) in the GRK1 gene in both patients. Proline 391 is not only within the functionally important catalytic domain, but is also a phylogenetically conserved amino acid residue among GRK1 orthologs and homologs. No mutation was found in the SAG gene. The unaffected parents were heterozygous carriers of the mutation. Both patients had night blindness, 1.5 BCVA for each eye, normal color vision, and typical fundus appearance with golden-yellow discoloration. The visual fields were normal in the male sibling. The ERGs showed no rod B waves, reduced standard combined responses, and markedly reduced single-flash cone and 30-Hz flicker responses in both patients. CONCLUSIONS: A novel homozygous GRK1 mutation (p.P391H) was found in 2 Japanese siblings with Oguchi disease. Visual function in the 2 patients has not deteriorated with age, indicating that the disease is stationary. This is the first report of any patient with GRK1-associated Oguchi disease with markedly reduced cone responses.

Compound heterozygous CNGA3 mutations (R436W, L633P) in a Japanese patient with congenital achromatopsia.

Congenital achromatopsia is a stationary retinal disorder with autosomal recessive inheritance that is characterized by loss of color discrimination, low visual acuity, photophobia, and nystagmus. This disorder has been shown to be associated with CNGA3, CNGB3, and GNAT2 mutations, and the frequency of mutations in the CNGA3 gene (encoding alpha subunit of the cone-specific cGMP-gated cation channel) was 23-33% in European populations. The aim of this study was to test the hypothesis that CNGA3 mutations are also responsible for congenital achromatopsia in Japanese patients. DNA from venous blood samples from a total of 14 patients from 13 Japanese pedigrees was prepared. Mutation screening of the CNGA3 gene was performed using direct sequencing and PCR-single-strand conformation polymorphism analysis. Compound heterozygous missense mutations (p.R436W and p.L633P, the latter of which was novel) were identified in one patient only, a 22-year-old female. Neither of these two mutations was found in 150 Japanese control individuals. The patient's parents and sister carried one of these mutations each but were not affected. No mutations in the CNGB3 or GNAT2 genes were identified in the patient. Clinically, best-corrected visual acuity was 0.1 in both eyes. No specific findings were obtained in funduscopy. Optical coherence topography revealed a normal foveal thickness but a 20% decrease in parafoveal thickness. Ganzfeld full-field electroretinograms (ERGs) showed normal responses in rod and mixed rod-plus-cone ERGs but no response in cone or 30-Hz flicker ERGs. Spectral sensitivity on a white background revealed a curve with only one peak at around 500 nm, which fits the absorption spectrum of human rhodopsin. L633, conserved among vertebrate orthologs of human CNGA3, is a hydrophobic residue forming part of the carboxy-terminal leucine zipper (CLZ) domain, which is functionally important in the mediation of intracellular interactions. To our knowledge, this is the first report of a Japanese complete achromat with CNGA3 mutations, and of any patient with a missense mutation within the CLZ domain. The outcome suggests low frequency (7%, 1/14) of CNGA3 mutations in Japanese patients.

Novel form of a single X-linked visual pigment gene in a unique dichromatic color-vision defect.

In normal trichromats, the long- (L) and middle-wavelength-sensitive (M) pigment genes are arranged in a head-to-tandem array on the X chromosome. Two amino acids at positions 277 and 285, encoded by exon 5 of the L and M genes, respectively, are essential for the spectral difference between L and M pigments whose spectral peaks are at approximately 560 and 530 nm. Intragenic or intergenic unequal crossing-over commonly occurs between the highly homologous L and M genes, resulting in red-green color vision deficiencies. The dichromacy is usually associated with a single L gene for deuteranopia or a single 5' L-M 3' hybrid gene with M-gene exon 5 for protanopia. We clinically diagnosed a total of 88 male dichromats using a Nagel model I anomaloscope, which included one unclassified subject in addition to 31 protanopes and 56 deuteranopes. The objective of this study was to characterize the phenotype of the subject and to determine the genotype of his X-linked pigment genes. The subject accepted not only any red-green mixture but also an extended yellow-scale range at each matching point (i.e. 20 to 32 scale units at the green primary and 3.5 to 6 scale units at the red primary). The slopes of regression lines were in the range of -0.34 to -0.23, while the mean slopes for the protanopes and deuteranopes were -0.38 and -0.01, respectively. Spectral sensitivity tests showed that the subject's curve was shifted between the protanope and deuteranope curves. Molecular analysis revealed a novel form of a single pigment gene with a unique arrangement of exon 5 (Y277 from the L gene and A285 from the M gene). The predicted lambdamax (541 to 546 nm) of the unique pigment was closer to the M than to the L pigment. Our outcome suggests that intragenic unequal crossing-over may have occurred between amino acid positions 279 and 283.

Compound heterozygous RDH5 mutations in familial fleck retina with night blindness.

PURPOSE: To describe the clinical features and genetic analysis of a 3-year-old boy diagnosed with familial fleck retina with night blindness. METHODS: The proband and his parents and grandparents were included. History, visual acuity and fundus examinations were evaluated. Bright-flash (rod-plus-cone) electroretinograms (ERGs) were recorded after 30 mins and 180 mins of dark adaptation. Mutation screening of the RDH5 gene encoding 11-cis retinol dehydrogenase was performed. RESULTS: The parents noticed the proband's night blindness when he was 2 years old. Best corrected visual acuity was 1.0 in both eyes. Fundus examinations revealed numerous yellow-white flecks of varying size and shape throughout the midperipheral to far peripheral retina in both eyes. The distribution, size and shape of the flecks were comparable to those seen in familial fleck retina with night blindness, rather than fundus albipunctatus. The ERGs showed extremely diminished responses after 30 mins of dark adaptation, but there were substantial increases in the amplitudes of both a- and b-waves when recorded after 180 mins of dark adaptation. Although a total of 19 RDH5 mutations have been found only in patients with fundus albipunctatus, compound heterozygous mutations, p.V177G and p.L310delinsEV, whose combination has not been previously reported, were found in the proband. The asymptomatic parents and one of the grandparents each carried one of the mutations, consistent with autosomal recessive transmission. CONCLUSION: Our study indicates that different mutations in the RDH5 gene can cause phenotypic variations of either fundus albipunctatus or familial fleck retina with night blindness.

Novel NR2E3 mutations (R104Q, R334G) associated with a mild form of enhanced S-cone syndrome demonstrate compound heterozygosity.

PURPOSE: We investigated the ophthalmic features of a mild form of enhanced S-cone syndrome (ESCS) in a 33-year-old Japanese female proband and 3 unaffected family members. A genetic analysis was performed. DESIGN: Genetic and observational case study. METHODS: Fundus examinations, optical coherence tomography (OCT), Goldmann visual field (VF) perimetry, color vision tests, spectral sensitivity, and full-field and spectral electroretinography (ERG) were performed. Mutation screening of the NR2E3 gene, which encodes a photoreceptor-specific orphan nuclear receptor, was performed with polymerase chain reaction amplification and direct sequencing. MAIN OUTCOME MEASURES: Mutations in the NR2E3 gene, fundus photographs, OCT images, VFs, spectral sensitivity, and ERG findings. RESULTS: The diagnosis of ESCS was made based on the distinctive spectral ERG findings: hypersensitivity to blue stimuli and hyposensitivity to red stimuli. The proband had good visual acuity, normal color vision, good central VFs, and nearly normal spectral sensitivity. Funduscopy showed degenerative lesions in the vascular arcades to the midperipheral retina. The OCT images showed a morphologically normal macular thickness. In the full-field ERG, low amplitudes of rod b-waves were detected. Waveforms between rod-plus-cone and cone ERGs were very similar. Mutation analysis identified 2 novel compound heterozygous missense mutations, p.R104Q and p.R334G, which reside in the DNA-binding domain (DBD) and ligand-binding domain (LBD), respectively. The unaffected parents carried one of these mutations each, consistent with autosomal recessive transmission. CONCLUSIONS: Our study suggests that the expression of these 2 mutants of NR2E3, acting as a dimer, is correlated with a mild form of ESCS in that full foveal function and retinal laminar structure are maintained, and certain rod responses are present. This may be explained by the possibility that the heterodimers encoded by the 2 mutant alleles retain certain NR2E3 functions through the respective intact DBD and LBD.

CYP4V2 mutations in two Japanese patients with Bietti's crystalline dystrophy.

Bietti's crystalline dystrophy (BCD) is an autosomal-recessive retinal dystrophy characterized by numerous glistening intraretinal dots scattered over the fundus, particularly in the posterior pole. The purpose of this study was to report mutations in the CYP4V2 gene (encoding a ubiquitously-expressed 525-amino acid sequence belonging to the CYP450 family) and to investigate the impact of the mutation on pre-mRNA splicing. DNA and RNA analyses were conducted using blood samples from two unrelated Japanese patients with BCD (a 46-year-old female and a 52-year-old male). In the female patient, a homozygous deletion/insertion mutation (g.IVS6-8_-1delc.802_810del/insGC) including the 3 -acceptor splice site was identified. Reverse transcription-PCR analysis revealed that the complete length of exon 7 (186 bp), is skipped, resulting in the in-frame deletion mutation (p.V268_E329del). Conversely, the male patient was a compound heterozygote for the deletion/insertion and novel nonsense (p.W340X) mutations. Clinically, the female patient had decreased visual acuity, constriction of visual fields, severely reduced amplitudes in both rod and cone electroretinograms (ERGs). Despite being 6 years older, the male patient presented with milder clinical manifestations having good visual acuity and substantial amplitudes in both rod and cone ERGs. Because the CYP4V2 truncated protein with the p.W340X mutation lacks 186 amino acids at the C-terminus, if expressed, it retains 62 amino acids encoded in exon 7, which are important for enzymatic activity. In the male patient, expression of both mutant alleles may compensate for the malfunction of each mutated protein and could explain why a milder form of BCD results from compound heterozygosity.