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Prevalence of color blindness.
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Color deficiency and inability to taste phenylthiourea.
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Visual and auditory neurotoxicity in patients receiving subcutaneous deferoxamine infusions.
Of 89 patients receiving nightly subcutaneous deferoxamine for transfusion-dependent thalassemia major or Diamond-Blackfan anemia, 13 presented with visual loss or deafness of acute onset or both. Detailed ophthalmologic, audiologic, and evoked-potential studies uncovered abnormalities caused by neurotoxicity in 27 more. Four patients with visual loss had optic neuropathy, with a marked decrease in acuity, loss of color vision, and delayed visual evoked potentials. Five asymptomatic patients had changes in the pigment of the retinal epithelium. The hearing loss was characterized by a high-frequency sensorineural deficit, which necessitated hearing aids in six patients. When deferoxamine was stopped, recovery of vision was complete in 2 patients and partial in 2, and in 22 patients with abnormal audiograms, reversal of the hearing deficit was complete in 4 and partial in 1. An analysis of the clinical data showed that members of the affected group were younger, had lower serum ferritin values, and were self-administering higher doses of deferoxamine per kilogram of body weight. Significantly lower doses of deferoxamine were being taken by patients without abnormalities than by those with visual symptoms, abnormal audiograms, or prolonged evoked potentials (P less than 0.001, less than 0.006, and less than 0.04, respectively). The data implicate high-dose deferoxamine as a central factor in the pathogenesis of the neurotoxicity. We strongly recommend careful regulation of the deferoxamine dosage and serial audiovisual monitoring in all patients receiving the drug.
Enhance communication: avoid red and green in slides.
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Epidemic optic neuropathy in Cuba--clinical characterization and risk factors.
BACKGROUND: From 1991 to 1993, epidemic optic and peripheral neuropathy affected more than 50,000 people in Cuba. The number of new cases decreased after the initiation of vitamin supplementation in the population. In September 1993, Cuban and U.S. investigators conducted a study to characterize and identify risk factors for the optic form of the syndrome. METHODS: We conducted ophthalmologic and neurologic examinations, assessed exposure to potential toxins, administered a semiquantitative food-frequency questionnaire, and assessed serum measures of nutritional status in 123 patients with severe optic neuropathy, matched for sex and age to randomly chosen normal subjects. RESULTS: In the case patients, prominent clinical features were subacute loss of visual acuity with field defects, diminished color vision, optic-nerve pallor, and decreased sensitivity to vibration and temperature in the legs. Tobacco use, particularly cigar smoking, was associated with an increased risk of optic neuropathy. The risk was reduced among subjects with higher dietary intakes of methionine, vitamin B12, riboflavin, and niacin and higher serum concentrations of antioxidant carotenoids. The risk was also reduced among subjects who raised chickens at home or had relatives living overseas--factors that may be indirect measures of increased food availability. CONCLUSIONS: The epidemic of optic and peripheral neuropathy in Cuba between 1991 and 1993 appears to be linked to reduced nutrient intake caused by the country's deteriorating economic situation and the high prevalence of tobacco use.
Blur and pseudoisochromatic colour vision tests.
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The color of two alphabets for a multilingual synesthete.
Interviews with a multilingual synesthete (MLS), who experiences colored letters for Roman and Cyrillic alphabets and for digits, revealed stable synesthetic experiences over 2 1/2 - 5 years. Colors of Cyrillic letters were based on Roman letters. Four Stroop tests involving both types of letters showed that MLS was able to name print color faster if the colors matched her synesthetic colors, showing that synesthesia is automatic. Letter-naming times for blocks of color were slower than those of actual letters, supporting unidirectionality of synesthesia. Stroop tests with Roman, but not Cyrillic, letters showed MLS acquired new temporary letter-color pairings and her color-naming times for these were not different from those for her original synesthetic colors.
An effect of luminance contrast on high-spatial-frequency tritanopia.
Luminance contrast was found to affect high-spatial-frequency tritanopia despite the S-cone coordinates of the stimuli being kept constant. This proves that a traditional account of artificial tritanopias based on the spatial resolution differences between the S-cone channel and the M- and L-cone channels is not applicable here. We suggest that the lack of spatial resolution in one of the post-receptor (rather than receptor) spatio-chromatic channels could be a cause of high-spatial-frequency tritanopia.
Functional photoreceptor loss revealed with adaptive optics: an alternate cause of color blindness.
There is enormous variation in the X-linked L/M (long/middle wavelength sensitive) gene array underlying "normal" color vision in humans. This variability has been shown to underlie individual variation in color matching behavior. Recently, red-green color blindness has also been shown to be associated with distinctly different genotypes. This has opened the possibility that there may be important phenotypic differences within classically defined groups of color blind individuals. Here, adaptive optics retinal imaging has revealed a mechanism for producing dichromatic color vision in which the expression of a mutant cone photopigment gene leads to the loss of the entire corresponding class of cone photoreceptor cells. Previously, the theory that common forms of inherited color blindness could be caused by the loss of photoreceptor cells had been discounted. We confirm that remarkably, this loss of one-third of the cones does not impair any aspect of vision other than color.
Fundamental studies of color vision from 1860 to 1960.
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Achromatopsia-associated mutation in the human cone photoreceptor cyclic nucleotide-gated channel CNGB3 subunit alters the ligand sensitivity and pore properties of heteromeric channels.
Cone photoreceptor cyclic nucleotide-gated (CNG) channels are thought to form by assembly of two different subunit types, CNGA3 and CNGB3. Recently, mutations in the gene encoding the CNGB3 subunit have been linked to achromatopsia in humans. Here we describe the functional consequences of two achromatopsia-associated mutations in human CNGB3 (hCNGB3). Co-expression in Xenopus oocytes of human CNGA3 (hCNGA3) subunits with hCNGB3 subunits containing an achromatopsia-associated mutation in the S6 transmembrane domain (S435F) generated functional heteromeric channels that exhibited an increase in apparent affinity for both cAMP and cGMP compared with wild type heteromeric channels. In contrast, co-expression of a presumptive null mutation of hCNGB3 (T383f.s.Delta C) with hCNGA3 produced channels with properties indistinguishable from homomeric hCNGA3 channels. The effect of hCNGB3 S435F subunits on cell-surface expression of green fluorescent protein-tagged hCNGA3 subunits and of non-tagged hCNGA3 subunits on surface expression of green fluorescent protein-hCNGB3 S435F subunits were similar to those observed for wild type hCNGB3 subunits, suggesting that the mutation does not grossly disturb subunit assembly or plasma membrane targeting. The S435F mutation was also found to produce changes in the pore properties of the channel, including decreased single channel conductance and decreased sensitivity to block by l-cis-diltiazem. Overall, these results suggest that the functional properties of cone CNG channels may be altered in patients with the S435F mutation, providing evidence supporting the pathogenicity of this mutation in humans. Thus, achromatopsia may arise from a disturbance of cone CNG channel gating and permeation or from the absence of functional CNGB3 subunits.
Macular dystrophy with protan genotype and phenotype studied with cone type specific ERGs.
PURPOSE: To determine the L- and M-cone driven ERG responses in a male patient with macular dystrophy and a protan phenotype. METHODS: We measured large field ERG thresholds to stimuli which modulated exclusively the L- or the M-cones or the two in various combinations (both in-phase and in counterphase). In none of the stimuli, the S-cones were modulated. Additionally, standard and multifocal ERGs were measured. Analysis of the L- and M-cone pigment genes was performed by means of PCR, RFLP analysis and DNA sequencing techniques. RESULTS: Macular dystrophy was revealed by the markedly abnormal multifocal ERGs in presence of near normal standard ERGs. The large field ERG responses were exclusively driven by the M-cones with enlarged thresholds when compared with otherwise normal protanopes. In addition, the M-cone driven ERG response phases were abnormal. Pigment gene analysis confirmed a protan genotype with the presence of a single 5'red/3'green hybrid pigment gene. CONCLUSIONS: Our novel stimulus technique allows a reliable analysis of the separate cone pathways even in cases with macular dysfunction. The increased thresholds and the abnormal phase behavior of the M-cone driven ERGs reflect altered mechanisms of the retinal physiology in this patient. The data strongly suggest that the macular dystrophy and the protanopia have independent origins.
Visual impairment and REP-1 gene mutations in Japanese choroideremia patients.
Choroideremia (CHM), an X-linked recessive hereditary disease, is an intractable chorioretinal dystrophy. The rate of disease progression of CHM reportedly shows considerable variability. A number of mutations involving the gene that codes for Rab escort protein-1 (REP-1) have been detected in CHM patients. We have analyzed REP-1 gene mutations of Japanese CHM patients. The present study was designed to investigate the clinical variability and the genotype to phenotype relationship in 15 Japanese CHM patients referred to the Department of Ophthalmology of Juntendo University Hospital. The clinical investigation of visual acuity, visual field, color vision and refraction revealed inter-individual variability. Mutation analyses of the REP-1 gene revealed 10 types of mutations in 13 patients from 11 families, including an insertion, small deletions, nonsense mutations and an A to CC mutation. In 13 CHM patients with detectable REP-1 gene mutations, no relationship of genotype to phenotype was detected. At present, we consider the REP-1 genotype to be an unreliable prognostic factor for counseling of CHM patients. In two patients from one family, no mutations were detected in coding regions of the REP-1 gene. These patients may have intron mutations of the REP-1 gene, not detectable by the techniques employed in this study, or other causative genes. Both were observed to have somewhat slower disease progression than the other 13 patients. More advanced analyses are necessary to answer questions regarding the genotype-phenotype relationship in CHM patients.
Clinical features of achromatopsia in Swedish patients with defined genotypes.
PURPOSE: To describe the clinical phenotype, with emphasis on the electrophysiological findings, of patients with autosomal recessive rod monochromacy (RM) and defined mutations in the CNGA3/CNGB3 genes. METHODS: RM patients from eight different families were included in the study. Their genotypes were determined by DNA sequencing and/or RFLP analysis of PCR-amplified genomic segments of the CNGA3 and CNGB3 genes. For comparison, we investigated one patient with blue-cone monochromacy (BCM). The clinical examination included best-corrected visual acuity, fundus examination, and full-field ERG. In six patients, the examination was complemented by multifocal ERG (MERG). RESULTS: Three patients had three different CNG3A genotypes. Five patients were homozygous and one patient compound heterozygous for a 1-bp deletion (1148delC) in the CNGB3 gene. All patients examined presented with a visual acuity of 0.1-0.15. Small residual cone responses were noted in four young RM patients. The oldest patient examined (age 47 years) presented with pigmentary changes in the mid-peripheral retina and concentric constrictions of the visual fields. CONCLUSIONS: Patients with RM and mutations in the CNGA3/CNGB3 genes presented a similar clinical phenotype, confirming the essential function of both the alpha- and beta-subunits of the cGMP-gated cation channel in cone photoreceptor function. Small remaining cone responses in a few of the younger patients and mid-peripheral pigmentary degenerations in the oldest patient examined indicate that there could be some degree of progression in retinal dysfunction in at least some patients with RM.
Infantile and childhood retinal blindness: a molecular perspective (The Franceschetti Lecture).
Much progress has been made in the past five years in the understanding of Leber congenital amaurosis (LCA) and allied early-onset retinal dystrophies, various forms of stationary sensory retinal blindness, and genes that are involved in the development of the retina. Uncomplicated Leber congenital amaurosis has been associated with mutations of six genes: GUCY2D (encoding RetGC-1) at 17p13.1, RPE65 at 1q31, CRX at 19q13.3, AIPLI at 17p13.1, CRB1 at 1q31-3, and RPGRIP at 14q11. A similar early-onset severe retinal degeneration phenotype has been associated with mutation of TULP1 at 6p21.3. Leber appreciated that the condition he described merged with the phenotypes of early childhood-onset severe retinal degenerations. This insight has been confirmed at the molecular level for mutations of GUCY2D, RPE65, CRX, AIPL1, and CRB1, which cause not only LCA, but also early-childhood and even adult-onset retinal degenerations. This paper reviews the new finding of LCA from mutations of CRB1 and discusses the molecular basis of X-linked blue monochromacy, autosomal recessive congenital achromatopsia from mutations of the genes for ACHM2 (CNGA3) and ACHM3 (CNGB3), X-linked congenital stationary night blindness (CSNB) from mutations of CACNA1F (incomplete CSNB) and NYX (complete CSNB), and the enhanced S-cone syndrome from mutation of the developmental gene, NR2E3 at 15q23, which appears to regulate the development of M- and L-cones from S-cones. These discoveries have opened new areas of cellular and developmental biology for future research into the causes of retinal blindness.