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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.

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.

ABSTRACT.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.