The landscape of submicroscopic structural variants at the OPN1LW/OPN1MW gene cluster on Xq28 underlying blue cone monochromacy.

Blue cone monochromacy (BCM) is an X-linked retinal disorder characterized by low vision, photoaversion, and poor color discrimination. BCM is due to the lack of long-wavelength-sensitive and middle-wavelength-sensitive cone photoreceptor function and caused by mutations in the OPN1LW/OPN1MW gene cluster on Xq28. Here, we investigated the prevalence and the landscape of submicroscopic structural variants (SVs) at single-base resolution in BCM patients. We found that about one-third (n = 73) of the 213 molecularly confirmed BCM families carry an SV, most commonly deletions restricted to the OPN1LW/OPN1MW gene cluster. The structure and precise breakpoints of the SVs were resolved in all but one of the 73 families. Twenty-two families-all from the United States-showed the same SV, and we confirmed a common ancestry of this mutation. In total, 42 distinct SVs were identified, including 40 previously unreported SVs, thereby quadrupling the number of precisely mapped SVs underlying BCM. Notably, there was no "region of overlap" among these SVs. However, 90% of SVs encompass the upstream locus control region, an essential enhancer element. Its minimal functional extent based on deletion mapping in patients was refined to 358 bp. Breakpoint analyses suggest diverse mechanisms underlying SV formation as well as in one case the gene conversion-based exchange of a 142-bp deletion between opsin genes. Using parsimonious assumptions, we reconstructed the composition and copy number of the OPN1LW/OPN1MW gene cluster prior to the mutation event and found evidence that large gene arrays may be predisposed to the occurrence of SVs at this locus.

Prevalence and genotypic frequency of color vision defects among primary schoolchildren in Adama Town, Eastern Ethiopia.

Color vision deficiency is a common X-linked genetic disorder affecting the day-to-day lives of individuals, in which school-aged children's academic performance can be negatively affected. The aim of this study was to evaluate the prevalence and genotypic frequency of congenital color vision defects (CVD), among primary schoolchildren in Adama, Ethiopia. A school-based cross-sectional study design was used. Students were purposively selected based on their ethnicity but were randomly selected from their sections, resulting in a final sample size estimated at 846 schoolchildren who had received informed consent from their families. Data was gathered using the Ishihara color vision test, 38-plate edition. The result of the study revealed that the total prevalence of CVD was much higher (5.6%) among the male children than that of the females, which was only about 1.79%. The prevalence rates of CVD among the targeted ethnic groups were found to be the highest among Amhara (7.45%) > Oromo (5.00%) > Gurage (2.13%) children, respectively, in descending order. 62.76% of the study subjects were homozygous dominant (AA), followed by those with a heterozygous genotype (Aa) (32.51%), and the remaining 4.73% had recessive (aa) genes.

Colour perception develops throughout childhood with increased risk of deficiencies in children born prematurely.

AIM: To quantify the impact of prematurity on chromatic discrimination throughout childhood, from 2 to 15 years of age. METHODS: We recruited two cohorts of children, as part of the TrackAI Project, an international project with seven different study sites: a control group of full-term children with normal visual development and a group of children born prematurely. All children underwent a complete ophthalmological exam and an assessment of colour discrimination along the three colour axes: deutan, protan and trytan using a DIVE device with eye tracking technology. RESULTS: We enrolled a total of 1872 children (928 females and 944 males) with a mean age of 6.64 years. Out of them, 374 were children born prematurely and 1498 were full-term controls. Using data from all the children born at term, reference normative curves were plotted for colour discrimination in every colour axis. Pre-term children presented worse colour discrimination than full-term in the three colour axes (p < 0.001). Even after removing from the comparison, all pre-term children with any visual disorder colour discrimination outcomes remained significantly worse than those from full-term children. CONCLUSION: While colour perception develops throughout the first years of life, children born pre-term face an increased risk for colour vision deficiencies.

ATF6 is essential for human cone photoreceptor development.

Endoplasmic reticulum (ER) stress and Unfolded Protein Response (UPR) signaling promote the pathology of many human diseases. Loss-of-function variants of the UPR regulator Activating Transcription Factor 6 (ATF6) cause severe congenital vision loss diseases such as achromatopsia by unclear pathomechanisms. To investigate this, we generated retinal organoids from achromatopsia patient induced pluripotent stem cells carrying ATF6 disease variants and from gene-edited ATF6 null hESCs. We found that achromatopsia patient and ATF6 null retinal organoids failed to form cone structures concomitant with loss of cone phototransduction gene expression, while rod photoreceptors developed normally. Adaptive optics retinal imaging of achromatopsia patients carrying ATF6 variants also showed absence of cone inner/outer segment structures but preserved rod structures, mirroring the defect in cone formation observed in our retinal organoids. These results establish that ATF6 is essential for human cone development. Interestingly, we find that a selective small molecule ATF6 signaling agonist restores the transcriptional activity of some ATF6 disease-causing variants and stimulates cone growth and gene expression in patient retinal organoids carrying these variants. These findings support that pharmacologic targeting of the ATF6 pathway can promote human cone development and should be further explored for blinding retinal diseases.

The construction of genetics teaching resources related to colour blindness and their application in genetics teaching.

Red-green colour blindness is a classic example for the teaching of X-linked recessive inheritance in genetics course. However, there are lots of types of color vision deficiencies besides red-green colour blindness. Different color vision deficiencies caused by different genes may have different modes of inheritance. In recent years, many research achievements on colour blindness have been made. These achievements could be used as teaching resources in genetics course. Here, we summarize the construction of genetics teaching resources related to colour blindness and their application in genetics teaching in several chapters such as introduction, cellular and molecular basis of genetics, sex-linked inheritance, chromosomal aberration, gene mutation and advances in genetics. Teacher could use the resources in class or after class with different teaching methods such as questioning teaching method and task method. It may expand students' academic horizons and inspire students' interest in genetics besides grasping basic genetic knowledge.

Visual evoked potentials in patients with congenital color vision deficiency.

BACKGROUND/AIM: Congenital color vision deficiency (CCVD) is an eye disease characterized by abnormalities in the cone cells in the photoreceptor layer. Visual evoked potentials (VEPs) are electrophysiological tests that physiologically examine the optic nerve, other visual pathways, and the visual cortex. The aim of this research was to determine whether there are VEP abnormalities in CCVD patients. METHODS: Patients with CCVD and healthy individuals were included in this prospective case-control study. Participants with eye disease or neurodegenerative disease were excluded from the study. Pattern reversal VEP (PVEP), flash VEP (FVEP), and optical coherence tomography were performed on all participants. RESULTS: Twenty healthy individuals (15 male) and 21 patients with CCVD (18 male) were included in the study. The mean ages of healthy individuals and patients with CCVD were 29.8 ± 9.6 and 31.1 ± 10.9 years (p = 0.804). Retinal nerve fiber layer thickness and central macular thickness values did not differ between the two groups. In PVEP, Right P100, Left N75, P100, N135 values were delayed in CCVD patients compared to healthy individuals (p = 0.001, p = 0.032, p = 0.003, p = 0.032). At least one PVEP and FVEP abnormality was present in nine (42.9%) and six (28.6%) of the patients, respectively. PVEP or FVEP abnormalities were found in 13 (61.9%) of the patients. CONCLUSION: This study indicated that there may be PVEP and FVEP abnormalities in patients with CCVD.

Evaluation of contrast sensitivity in patients with congenital red-green color vision deficiency.

PURPOSE: To evaluate mesopic and photopic contrast sensitivity in patients with congenital red-green color vision deficiency regarding with and without glare conditions and to compare these findings with age- and gender-matched healthy controls with normal color vision. METHODS: Patients with congenital red-green color vision deficiency and age- and gender-matched healthy controls were included in this cross-sectional comparative study. Contrast sensitivity measurements were taken from all subjects in 4 different conditions; binocular mesopic-without glare, mesopic-with glare, photopic-without glare, photopic-with glare, and the results were compared. RESULTS: Twenty one patients with color vision deficiency (13 deuteranopic, 8 protanopic) and 22 age- and gender-matched healthy controls were included in the study. The mean age was 35.2 ± 13.5 years in the protan group, 30.6 ± 7.7 years in the deutan group, 32.0 ± 8.8 years in the control group, and there was no significant difference in age between the groups (P > 0.05). The mean mesopic and photopic contrast sensitivity values of the groups at all spatial frequencies (1.5, 3, 6, 12, 18 cpd) were not statistically significant when evaluated by the multifactor repeated measures test of ANOVA to evaluate the effect of light conditions (with and without glare) (P > .05). CONCLUSION: Mesopic and photopic contrast sensitivity values of patients with congenital red-green color vision deficiency were similar to healthy controls regarding with and without glare conditions.

A duplication on chromosome 16q12 affecting the IRXB gene cluster is associated with autosomal dominant cone dystrophy with early tritanopic color vision defect.

Cone dystrophies are a rare subgroup of inherited retinal dystrophies and hallmarked by color vision defects, low or decreasing visual acuity and central vision loss, nystagmus and photophobia. Applying genome-wide linkage analysis and array comparative genome hybridization, we identified a locus for autosomal dominant cone dystrophy on chromosome 16q12 in four independent multigeneration families. The locus is defined by duplications of variable size with a smallest region of overlap of 608 kb affecting the IRXB gene cluster and encompasses the genes IRX5 and IRX6. IRX5 and IRX6 belong to the Iroquois (Iro) protein family of homeodomain-containing transcription factors involved in patterning and regionalization of embryonic tissue in vertebrates, including the eye and the retina. All patients presented with a unique progressive cone dystrophy phenotype hallmarked by early tritanopic color vision defects. We propose that the disease underlies a misregulation of the IRXB gene cluster on chromosome 16q12 and demonstrate that overexpression of Irx5a and Irx6a, the two orthologous genes in zebrafish, results in visual impairment in 5-day-old zebrafish larvae.

Functional evaluation allows ACMG/AMP-based re-classification of CNGA3 variants associated with achromatopsia.

PURPOSE: CNGA3 encoding the main subunit of the cyclic nucleotide-gated ion channel in cone photoreceptors is one of the major disease-associated genes for achromatopsia. Most CNGA3 variants are missense variants with the majority being functionally uncharacterized and therefore hampering genetic diagnosis. In light of potential gene therapy, objective variant pathogenicity assessment is essential. METHODS: We established a medium-throughput aequorin-based luminescence bioassay allowing mutant CNGA3 channel function assessment via quantification of CNGA3 channel-mediated calcium influx in a cell culture system, thereby enabling American College of Medical Genetics and Genomics/Association for Molecular Pathology-based variant re-classification. RESULTS: We provide functional read-out obtained for 150 yet uncharacterized CNGA3 missense substitutions of which 55 were previously categorized as variants of uncertain significance (VUS) identifying 25 as functionally normal and 125 as functionally abnormal. These data enabled the American College of Medical Genetics and Genomics/ Association for Molecular Pathology-based variant re-classification of 52/55 VUS as either benign, likely benign, or likely pathogenic reaching a VUS re-classification rate of 94.5%. CONCLUSION: Our aequorin-based bioassay allows functionally ensured clinical variant interpretation for 150 CNGA3 missense variants enabling and supporting VUS re-classification and assuring molecular diagnosis to patients affected by CNGA3-associated achromatopsia, hereby identifying patients eligible for future gene therapy trials on this disease.

Assessment of visual function and the neuroretina in subjects diagnosed with congenital anomaly of color vision.

This cross-sectional and observational study includes 50 eyes of subjects with color blindness and 50 eyes of control subjects. Visual function (visual acuity, contrast sensitivity, and color vision) and neuroretinal structure were assessed in all subjects using optical coherence tomography (OCT). Significant thinning of the retinal nerve fiber layer, ganglion cell layer, and retina were observed in the color blindness group. Significant thinning was also recorded in layers that involve photoreceptor nuclei (between the outer limiting layer and the Bruch membrane and between the outer plexiform layer and the outer limiting membrane). OCT evaluation based on retinal segmentation is a rapid (5-10 minutes) non-invasive technique and seems to be a good biomarker of color blindness.

Frequency-dependent retinal responsiveness to sinusoidal electrical stimulation in achromatopsia.

Recently, we proposed a method to assess cell-specific retinal functions based on the frequency-dependent responses to sinusoidal transcorneal electrostimulation. In this study, we evaluated the alterations in responsiveness in achromatopsia patients to explore the frequency-selectivity of photoreceptors. The electrical stimulation was applied to one eye of genetically confirmed achromatopsia patients via corneal electrodes. The stimulus was composed of amplitude-modulated sine waves with variable carrier frequencies (4-30 Hz) and a steady low-frequency envelope. The retinal responsiveness across the spectrum was calculated based on the velocity and the synchronicity of the electrically evoked pupillary oscillations. Achromats displayed a characteristic peak in responsiveness in the 6-10 Hz range. In contrast, stimulus frequencies above 16 Hz elicited only weak pupil responses and weak phosphenes. Compared to the tuning curve of the healthy retina, responses to low-frequency stimulation appear to reflect mainly rod activation while higher frequencies seem to activate cones. The possibility to examine cell-specific retinal functions independently from their responses to light may improve our understanding of the structural changes in the retina induced by gene therapy.

A demonstration of cone function plasticity after gene therapy in achromatopsia.

Recent advances in regenerative therapy have placed the treatment of previously incurable eye diseases within arms' reach. Achromatopsia is a severe monogenic heritable retinal disease that disrupts cone function from birth, leaving patients with complete colour blindness, low acuity, photosensitivity and nystagmus. While successful gene-replacement therapy in non-primate models of achromatopsia has raised widespread hopes for clinical treatment, it was yet to be determined if and how these therapies can induce new cone function in the human brain. Using a novel multimodal approach, we demonstrate for the first time that gene therapy can successfully activate dormant cone-mediated pathways in children with achromatopsia (CNGA3- and CNGB3-associated, 10-15 years). To test this, we combined functional MRI population receptive field mapping and psychophysics with stimuli that selectively measure cone photoreceptor signalling. We measured cortical and visual cone function before and after gene therapy in four paediatric patients, evaluating treatment-related change against benchmark data from untreated patients (n = 9) and normal-sighted participants (n = 28). After treatment, two of the four children displayed strong evidence for novel cone-mediated signals in visual cortex, with a retinotopic pattern that was not present in untreated achromatopsia and which is highly unlikely to emerge by chance. Importantly, this change was paired with a significant improvement in psychophysical measures of cone-mediated visual function. These improvements were specific to the treated eye, and provide strong evidence for successful read-out and use of new cone-mediated information. These data show for the first time that gene replacement therapy in achromatopsia within the plastic period of development can awaken dormant cone-signalling pathways after years of deprivation. This reveals unprecedented neural plasticity in the developing human nervous system and offers great promise for emerging regenerative therapies.

An early onset cone dystrophy due to CEP290 mutation: a case report.

PURPOSE: Biallelic mutations in the CEP290 gene cause early onset retinal dystrophy or syndromic disease such as Senior-Loken or Joubert syndrome. Here, we present an unusual non-syndromic case of a juvenile retinal dystrophy caused by biallelic CEP290 mutations imitating initially the phenotype of achromatopsia or slowly progressing cone dystrophy. METHODS: We present 13 years of follow-up of a female patient who presented first with symptoms and findings typical for achromatopsia. The patient underwent functional and morphologic examinations, including fundus autofluorescence imaging, spectral-domain optical coherence tomography, electroretinography, color vision and visual field testing. RESULTS: Diagnostic genetic testing via whole genome sequencing and virtual inherited retinal disease gene panel evaluation finally identified two compound heterozygous variants c.4452_4455del;p.(Lys1484Asnfs*4) and c.2414T > C;p.(Leu805Pro) in the CEP290 gene. CONCLUSIONS: CEP290 mutation causes a wide variety of clinical phenotypes. The presented case shows a phenotype resembling achromatopsia or early onset slowly progressing cone dystrophy.

Pro-Con Debate: Perioperative Research Should Be Color-Blind.

Profound racial and ethnic disparities have been documented in health and health care outcomes in recent decades. Some researchers have erroneously ascribed these inequities to biological variations, prompting debate as to how, or even if, race and ethnicity should be included as an outcome variable. Color blindness is a racial ideology with roots in constitutional law that posits that equality is best achieved by disregarding the racial and ethnic characteristics of the individual. Color consciousness, in contrast, approaches disparities with the knowledge that experiences related to one's race and ethnicity influence an individual's health and well-being. In this Pro-Con commentary article, we discuss the concept of color blindness and debate its use as an approach in medicine and research.

Screening for mild anomalous trichromacy using the Ishihara plates test.

The Ishihara plates test is one of the most established and widely used means of identifying color vision deficiencies. However, literature examining the effectiveness of the Ishihara plates test has identified weaknesses, particularly when screening for milder anomalous trichromacy. We constructed a model of the chromatic signals expected to contribute to false negative readings by calculating, for particular anomalous trichromatic observers, the differences in chromaticity between the ground and pseudoisochromatic portions of plates. Predicted signals from five plates were compared for seven editions of the Ishihara plates test, for six observers with three severities of anomalous trichromacy, under eight illuminants. We found significant effects of variation in all of these factors other than edition on the predicted color signals available to read the plates. The impact of edition was tested behaviorally with 35 observers with color vision deficiency and 26 normal trichromats, which corroborated the minimal effect of edition predicted by the model. We found a significant negative relationship between predicted color signals for anomalous trichromats and behavioral false negative plate readings (ρ=-0.46, p=0.005 for deuteranomals, ρ=-0.42, p=0.01 for protanomals), suggesting that residual observer-specific color signals in portions of plates designed to be isochromatic may be contributing to false negative readings, and validating our modeling approach.

Effect of laser eye protection devices on color perception.

Laser eye protection (LEP) devices may alter how colors are perceived in visual displays. This study investigates changes in color perception experienced by color-normal observers while wearing LEPs. Color perception with and without LEPs was measured using clinical color tests: City University Color Assessment and Diagnosis, Konan Medical ColorDx CCT-HD, and Farnsworth-Munsell 100-Hue. All LEPs induced a shift in color perception. The level of change in color perception significantly varied across LEPs. Consideration should be made when designing color displays where LEP devices are worn.

The Verriest Lecture: Pathways to color in the eye and brain.

In common with the majority of New World monkeys, marmosets show polymorphic color vision by allelic variation of X-chromosome genes encoding opsin pigments in the medium/long wavelength range. Male marmosets are thus obligate dichromats ("red-green color blind"), whereas females carrying distinct alleles on X chromosomes show one of three trichromatic phenotypes. Marmosets thus represent a "natural knock-out" system enabling comparison of red-green color vision in dichromatic and trichromatic visual systems. Further, study of short-wave (blue) cone pathways in marmosets has provided insights into primitive visual pathways for depth perception and attention. These investigations represent a parallel line to clinical research on color vision defects that was pioneered in studies by Guy Verreist, whom we honor in this eponymous lecture.

Clinical analysis of the Konan-Waggoner D15 color vision test using the Surface-Pro display.

This work expands on our previous comparison of the Konan-Waggoner D15 (KW-D15) and Farnsworth D15 (F-D15). Sixty subjects with normal color vision and 68 subjects with a red-green color vision defect participated in the study. The KW-D15 had good agreement with the F-D15 for both pass/fail and classification across all failure criteria. The agreement was slightly better if subjects had to pass on 2/3 trials compared with just the first trial. The KW-D15 is an adequate substitute for the F-D15, with the caveat that the KW-D15 might be slightly easier to pass than the F-D15 for deutans.

Word and color impressions measured with normal and simulated deutan color stimulus sets in color vision normal and deuteranopic observers.

Impressions of nine semantic words expressing abstract meanings were measured by a color selection process using twelve hues from vivid tone in the Practical Color Coordinate System (PCCS) as well as White, Grey and Black (as a normal color stimulus set) in a paired comparison method (Experiment 1). Color impressions were rated using 35 paired words in a semantic differential (SD) method (Experiment 2). The data of ten color vision normal (CVN) and four deuteranopic observers were analyzed separately by principal component analysis (PCA). Our previous study [J. Opt. Soc. Am. A37, A181 (2020)JOAOD60740-323210.1364/JOSAA.382518] using these methods indicated that deuteranopes could understand the impression of all colors if the color names can be recognized, even if deuteranopes cannot perceive redness and greenness. In this study, we also used a simulated deutan color stimulus set in which colors were modified to simulate the color appearance in deuteranopes by using Brettel-Viénot-Mollon's model to investigate how these simulated deutan colors would be treated by the deutan observers. In the CVN and deutan observers, color distributions of the principal component (PC) loading values in Experiment 1 were close to the PCCS hue circle in the normal colors, and those of the simulated deutan colors could be fitted by ellipses, but there were wide gaps of 73.7° (CVNs) and 89.5° (deutan) where only "White" existed. The word distributions as the PC score values could also be fitted by ellipses and are moderately similar between stimulus sets, but the fitting ellipses were considerably compressed in the minor axis directions in the deutan observers, although categories of words were similar between observer groups. The word distributions in Experiment 2 were not statistically different between the observer groups and the stimulus sets. The color distribution of the PC score values were statistically different, but tendencies of the color distributions were similar between observers. The color distributions of the normal colors could be fitted by ellipses, similar to the hue circle, and those of the simulated deutan colors could be fitted by cubic function curves. These results suggest that both of the stimulus sets were perceived as one dimensional and as a monotonic series of colors by a deuteranope, but the deuteranope can recognize the difference of the stimulus sets and recall the color distributions of each set, similar to those in the CVN observers.

Elimination of the color discrimination impairment along the blue-yellow axis in patients with hypothyroidism after treatment with levothyroxine as assessed by the Farnsworth-Munsell 100 hue test.

Our previous study has shown that individuals with untreated hypothyroidism display significantly higher partial error scores (P E S) along the blue-yellow axis compared to the red-green axis than normal individuals using the Farnsworth-Munsell 100 hue test [J. Opt. Soc. Am. A37, A18 (2020)JOAOD60740-323210.1364/JOSAA.382390]. We wished to determine how color discrimination may change when hypothyroidism has been treated to the point of euthyroidism. Color discrimination was reassessed for 17 female individuals who had undergone treatment for hypothyroidism, and the results were compared with 22 female individuals without thyroid dysfunction. No statistically significant difference was found in the total error score (T E S) for the first and second measurements for both groups (p>0.45). The P E S for the hypothyroid group improved significantly in the previously impaired color regions after the treatment. Color discrimination defects found in untreated hypothyroidism can be negated with treatment of the condition over an appropriate time period.