January 2006
Volume 47, Issue 1
Free
Biochemistry and Molecular Biology  |   January 2006
H244R VSX1 Is Associated with Selective Cone ON Bipolar Cell Dysfunction and Macular Degeneration in a PPCD Family
Author Affiliations
  • Sophie Valleix
    From the Laboratoire de Biochimie et Génétique Moléculaire, Hôpital Cochin, Paris, France; the
    Institut Cochin, Département de Génétique, Développement et Pathologie Moléculaire, Institut National de la Santé et de la Recherche Médicale (INSERM)-U567, Paris, France; the
  • Brigitte Nedelec
    Institut Cochin, Département de Génétique, Développement et Pathologie Moléculaire, Institut National de la Santé et de la Recherche Médicale (INSERM)-U567, Paris, France; the
  • Florence Rigaudiere
    Unité INSERM 592-Université Paris 7, Hôpital Lariboisière–Saint Louis, Paris, France; the
  • Paul Dighiero
    Service d’Ophtalmologie, Centre Hospitalo-Universitaire de Poitiers, France; and the
  • Yves Pouliquen
    Service d’Ophtalmologie, Hôpital Hôtel-Dieu, Paris, France.
  • Gilles Renard
    Service d’Ophtalmologie, Hôpital Hôtel-Dieu, Paris, France.
  • Jean-François Le Gargasson
    Unité INSERM 592-Université Paris 7, Hôpital Lariboisière–Saint Louis, Paris, France; the
  • Marc Delpech
    From the Laboratoire de Biochimie et Génétique Moléculaire, Hôpital Cochin, Paris, France; the
    Institut Cochin, Département de Génétique, Développement et Pathologie Moléculaire, Institut National de la Santé et de la Recherche Médicale (INSERM)-U567, Paris, France; the
Investigative Ophthalmology & Visual Science January 2006, Vol.47, 48-54. doi:10.1167/iovs.05-0479
  • Views
  • PDF
  • Share
  • Tools
    • Alerts
      ×
      This feature is available to Subscribers Only
      Sign In or Create an Account ×
    • Get Citation

      Sophie Valleix, Brigitte Nedelec, Florence Rigaudiere, Paul Dighiero, Yves Pouliquen, Gilles Renard, Jean-François Le Gargasson, Marc Delpech; H244R VSX1 Is Associated with Selective Cone ON Bipolar Cell Dysfunction and Macular Degeneration in a PPCD Family. Invest. Ophthalmol. Vis. Sci. 2006;47(1):48-54. doi: 10.1167/iovs.05-0479.

      Download citation file:


      © 2016 Association for Research in Vision and Ophthalmology.

      ×
  • Supplements
Abstract

purpose. To elucidate the retinal dysfunction and the molecular basis of posterior polymorphous corneal dystrophy (PPCD) associated with macular dystrophy, both inherited in a dominant manner through a three-generation family.

methods. Ophthalmologic examinations including slit lamp examination, visual acuity tests, fundus visualization by scanning laser ophthalmoscopy, fluorescein angiography, color vision tests, electro-oculography, photopic and scotopic electroretinography (ERG) according to the International Society for Clinical Electrophysiology of Vision (ISCEV) protocols, and oscillatory potential (OP) recordings were conducted on affected family members. Corneal button from one affected patient was examined by transmission electron microscopy. All exons and intron-exon boundaries of the VSX1 and the COL8A2 genes were amplified by polymerase chain reaction and sequenced.

results. The presence of endothelial cells that have epithelial-like features with multiple layers, desmosomal junctions, and microvillous projections supports the diagnosis of PPCD. Sequence analysis indicated that the H244R variant in the VSX1 segregated with corneal and macular disease phenotypes in this family. Electrophysiologic studies indicated normal scotopic ERG findings, decreased amplitude of the photopic b-wave, photopic OP2 and OP3 barely recordable with a preserved OP4 amplitude, and variably decreased 30-Hz flicker amplitude.

conclusions. The human VSX1 is required for cone ON bipolar cell function but not for rod and cone OFF bipolar cells, giving a unique example of such a selective heritable retinal defect in humans. Furthermore, the authors provide the first clinical support for a new alternative role of VSX1 in cone biology, probably similar to that proposed for its goldfish ortholog during retinal differentiation.

The human visual system homeobox gene VSX1 is a paired-like gene containing a highly conserved domain, denoted as CVC because it was originally identified in mouse Chx10, goldfish Vsx1 and Caenorhabditis elegans Ceh-10 genes. 1 2 3 Although the role of this domain must be more defined, it is necessary for transcriptional regulation and efficient ubiquitination for the degradation of Vsx1 by the 26S proteasome. 4 However, the CVC-domain of Vsx1 is required for protein function given that mutations within the CVC domain of the Ceh-10 gene are lethal because of defects in interneuron formation. 5 Numerous orthologs and homologs of these genes have now been isolated, and all have demonstrated a high expression level in the inner nuclear layer (INL) of developing or adult retinas, suggesting that homeobox/CVC proteins play a role in bipolar interneuron biology. 6 7 8 9 10 11 12 13 Understanding the role of such genes is a significant challenge because interneurons are thought to constitute most cells in the nervous system and relatively little is known concerning their functioning. The Vsx1 gene was initially identified in goldfish, a species in which retinogenesis and retinal regeneration after injury is maintained throughout life, in contrast to mammals. 1 In adult goldfish retina, Vsx1 expression is restricted to bipolar cells (BCs), suggesting that this gene stabilizes the differentiated state of these interneuron cells. However, in the immature retina, Vsx1 is also expressed, transiently, in mitotically active cone, horizontal, and bipolar cell progenitors at the proliferative retinal margin before it is switched off in retinal cells other than BCs when differentiation begins. 1 12 Therefore, this specific BC expression results from a tightly controlled temporal and spatial downregulation of Vsx1. This restrictive expression pattern of Vsx1 closely parallels that of the mouse Chx10 gene, which is indispensable for retinal progenitor cell (RPC) proliferation during the early stages of retinogenesis and for differentiation of BCs. 2 11 14 Recent results provided by the engineering of Vsx1-null alleles in mice implicated Vsx1 in retinal physiology. 15 16 Although these mice had normal eye appearance with typical corneal and retinal histology, retinal electrophysiological experiments indicated that Vsx1 regulates the visual photopic pathway and that it is probably specifically required for the late differentiation of cone OFF-BC. Furthermore, among Vsx1-BCs, some are recoverin positive whereas others are recoverin negative, suggesting heterogeneity between BCs in which Vsx1 exerts its function. 16 Finally, several lines of evidence support the view that Vsx1 retinal expression is downregulated in a Vsx1-dependent manner, suggesting that Vsx1 is required in a feedback loop to negatively regulate the generation of cone bipolar interneurons. 16  
In humans, VSX1 missense mutations were unexpectedly found to be associated with dominant posterior polymorphous corneal dystrophy (PPCD) and keratoconus, two conditions known to affect solely corneal tissues. 17 Although patients with PPCD showed no clinical retinal phenotype, they probably had reduced scotopic activity, as suggested by electroretinography (ERG) data. 17 More recently, ocular and nonocular abnormalities, including severe craniofacial malformations, central nervous system defects, and decreased auditory functions, were reported in a VSX1 family, suggesting therefore that the phenotypic spectrum of VSX1 appears broader than previously believed. Moreover, retinal electrophysiological experiments performed on these patients indicated, in addition to a cone bipolar pathway defect, a subclinical macular impairment in some patients with VSX1, though no evident macular phenotype was detected in the patients. 18  
This report describes, for the first time, a family with PPCD and severe macular dystrophy in which both traits were inherited in a dominant manner, highlighting a new alternative role of VSX1 in cone photoreceptors. In addition, these patients showed an unusual postreceptoral retinal defect, providing a valuable resource for understanding the role of VSX1 in specific retinal bipolar cell pathways. 
Materials and Methods
Patients
Nine members of a family (II.1, III.1, III.2, III.3, IV.1, IV.2, IV.3, IV.4, IV.5) were examined and followed up at the Department of Ophthalmology of Hôtel-Dieu Hospital for a period of 30 years. Medical records were recently obtained for two other family members (III.5, III.6) from an ophthalmologist of their community. A standard ophthalmologic examination including measurement of visual acuity, Goldmann visual field testing, determination of intraocular pressure, gonioscopy, and slit lamp examination was performed. Endothelial specular microscopy was performed in four members (III.1, IV.1, IV.2, IV.4), and fluorescein angiography was performed in four other members (III.1, IV.1, IV.2, IV.3). Informed consent was obtained from all participating members of this family, in accordance with the guidelines established by the ethics committees of the Hôtel-Dieu Hospital and Cochin Hospital in Paris. 
Histopathology
Corneal transplantation was performed on the proband (III.1), and his corneal button was examined by light and transmission electron microscopy using standard procedures. 
Mutation Detection and Restriction Enzyme Analysis
Genomic DNA was extracted from peripheral blood leukocyte samples, in accordance with the tenets of the Declaration of Helsinki, and each exon with exon-intron junctions of the VSX1 and COL8A2 genes was amplified by polymerase chain reaction (PCR) using the appropriate forward and reverse sets of primers previously reported. 17 19 PCR products, purified and sequenced on both strands, were resolved on an automatic fluorometric DNA sequencer (ABI Prism 3100 Genetic Analyser; Applied Biosystems, Foster City, CA). Because the nucleotide substitution (A→G) abolishes a BtsI restriction site, PCR-amplified fragments from a control population of 100 persons (200 chromosomes in total) were digested with BtsI (Boehringer Mannheim, Mannheim, Germany), which recognizes the wild-type allele (5′-GCAGTGNN-3′) but not the mutant (5′-GCAGCGNN-3′), after which electrophoresis was performed on a 2% agarose gel. 
Psychological and Electrophysiological Tests
All three children of the fourth generation (IV.1, born in 1980; IV.2, born in 1982; IV.3, born in 1986) underwent three visual explorations. The father (III.1, 1952) underwent electro-oculography (EOG) and ERG recordings only because of his poor vision and severe photophobia. First, color vision was tested with saturated and desaturated color tests (D-15; Lanthony, Luneau, France). These tests were separately viewed by each eye under calibrated daylight (two fluorescent lamps; TLD 36W/95; Philips, Amsterdam, The Netherlands). Second, to obtain electrophysiological recordings, ERG and EOG were performed (Metrovision device; Lille, France; ERG corneal electrodes; Dencott, Paris France; EOG skin electrodes; Comepa, Bagnolet, France). They were conducted according to international ISCEV-EOG and ISCEV-ERG protocols. 20 21 Briefly, after 20-minute adaptation to dark with pupils fully dilated, the scotopic response (i.e., the response of the rod system) and the maximal combined response (i.e., the combined responses of the rod and cone systems) were recorded. Then, after a 10-minute adaptation to light and on a photopic background (30 cd/m2), the oscillatory potentials (OPs) and the photopic responses, including the low (1 Hz) and the high temporal frequency responses (30 Hz) (respectively designed as the cone response and the flicker response) were recorded. The cone response represents that of the three cone systems, and the flicker response is limited to the response of the two major L and M cone systems. The EOG was first recorded and followed by the ERG recordings. Finally, eye fundi of the three patients were visualized by means of a scanning laser ophthalmoscope (SLO; personal prototype). The aspect of each SLO eye fundus was tape recorded together with the localization of the patient’s preferred retinal locus (PRL). Comparison of its position with the patient’s clinical visual acuity gives good indication of the functioning mode of the PRL. 
Results
Corneal and Retinal Phenotypes
The family reported here is a nonconsanguineous kindred from Poland that includes eight PPCD-affected members over three generations (Fig. 1A) . The affected male (III.1), who was the most affected member of the family, was first referred to the Department of Ophthalmology of Hôtel-Dieu Hospital at the age of 25 years to undergo corneal transplantation. Slit lamp examination showed numerous corneal endothelial vesicular lesions often grouped in clusters and surrounded by a gray halo, diffuse thickening of the Descemet’s membrane with bandlike lesions, and islands of abnormal endothelial cells with multilamellar pattern. Specular microscopy revealed endothelial changes with pleomorphism, polymegathism, and endothelial cell loss (500/mm2), suggestive of severe endothelial damage (data not shown). Optical, scanning, and transmission electron microscopy analysis of the corneal button from this proband indicated granular deposits in the posterior stroma, thickened Descemet’s membrane composed of three layers with a normal anterior fetal zone, an intermediate anarchic zone composed of fibrils, and long and short collagen fibers, and an irregular adult zone with some long period collagen fibers (data not shown). This layer was lined posteriorly by degenerate overlapping endothelial cells that have epithelial-like features with multiple layers, desmosomal junctions, and microvillous projections (Fig. 1B) . These abnormal findings suggest that corneal endothelial cells have degenerated and have been progressively replaced by pseudoepithelial cells producing collagen fibers and fibrils. 
The proband of this family (III.1) also exhibited bilateral macular dystrophy that progressively worsened over a period of 30 years. In early examinations, the proband experienced severely decreased visual acuity and photophobia, whereas nocturnal and peripheral visions were unaffected. At that time, his best-corrected visual acuity was 0.2 in the right eye and 0.1 in the left eye. His visual field showed a bilateral central scotoma. At ophthalmoscopy, the fundi showed asymmetric macular lesions with white polymorphous flecks, sparing the fovea. Fluorescein angiography revealed bilateral parafoveal hyperfluorescent well-circumscribed lesions, with central hypofluorescence, giving the aspect of “bull’s-eye ” lesions (Fig. 2A) . At the present time, the proband’s visual acuity is limited to counting fingers, with preserved peripheral and nocturnal vision. Fluorescein angiography has demonstrated the progression of macular degeneration, which now also involves the fovea, giving a “beaten-metal ” appearance (Fig. 2B) . Two of the proband’s children (IV.1, IV.3) were also diagnosed with PPCD and macular dystrophy at 11 and 4 years of age, respectively, whereas another child (IV.2) was not clinically affected. The proband’s father (II.1), who died 25 years ago, was known to have a moderate form of PPCD, with subtle eye fundus abnormalities. Four other family members were recently diagnosed with mild PPCD (III.3, III.5, IV.4, IV.6). These patients also had decreased visual acuity, severe photophobia, and mild atrophic macular lesions observed at funduscopy, demonstrating that corneal and retinal traits were inherited in a dominant manner in this family. 
Mutation Detection
It has been previously reported that missense mutations in VSX1 or in the gene encoding the alpha2 chain of type VIII collagen (COL8A2) caused autosomal dominant PPCD. 17 19 Genetic screening of these two genes in the proband’s DNA revealed a heterozygous nucleotide variation in the VSX1 gene, corresponding to an A→G transition, which predicted the change of histidine to arginine at amino acid position 244 in VSX1 (Fig. 1C) . Sequence analysis indicated that this H244R variant was absent from the proband’s clinically unaffected child (IV.2), whereas both clinically affected children (IV.1, IV.3) carried this mutation in the heterozygous state. This variant was also present in affected family members (III.3, IV.4) and absent in the unaffected (IV.5) patient, thus demonstrating that this VSX1 variant segregated with both disease phenotypes in this family. The H244R VSX1 variant has previously been identified in a familial case of keratoconus and in two apparently asymptomatic heterozygous persons. 17 Restriction analysis from our control population showed that the H244R allele was present in one of the 200 chromosomes studied (data not shown). The number of control chromosomes tested for this variant from PPCD or keratoconus studies now available is 1004, and only three control chromosomes have been found positive. 17 Therefore, the frequency of this variant is estimated at 0.30% instead of the 0.70% initially published. In addition, VSX1 has also been screened in 161 pedigrees affected with various anterior segment abnormalities by Semina and colleagues, 22 and no mutations were found. All these data indicate that the H244R variant is not widespread and that it cannot be considered a common variant. PPCD is a slowly progressive corneal disorder that leads to a variable degree of visual impairment in adulthood, but usually this condition goes unnoticed throughout life and affected persons are diagnosed by chance, explaining why most PPCD cases are considered sporadic. Therefore, we cannot rule out the possibility that the positive controls could have mild, undiagnosed keratoconus, or PPCD, or even subclinical retinal dysfunction. 
Psychological and Electrophysiological Tests
We performed, on four family members (IV.1, IV.2, IV.3, III.1), a series of visual tests to define the level of the retinal defects and to quantify their extent. Color vision results showed a protan axis of confusion for each eye with the saturated and desaturated tests for patient IV.1. For patient IV.2, color vision data were normal. For patient IV.3, results of the saturated test were normal for both eyes, and those of the desaturated test showed many lines of confusion without any defined axis, similar to what is recorded in advanced macular dystrophies (data not shown). Then, the proband’s children eye fundi were visualized by means of a SLO. The aspect of each SLO eye fundus was tape recorded, together with the localization of the patient’s preferred retinal locus (PRL). Comparison of its position with the patient’s clinical visual acuity gives good indications of the functioning mode of the PRL. The SLO eye fundi of patient IV.1 showed a round inhomogeneous macular area of approximately 10°, centered on the fovea. His visual acuity was 0.6, and his PRL were located inside the pathologic area, indicating that his small foveal areas are still functioning despite the dystrophic aspect of the macula (Fig. 2C) . In contrast, the SLO eye fundi of patient IV.3 showed that her PRL was located outside the macular lesions, on the upper part of the atrophic areas, with a visual acuity of 0.4, suggesting functional retinal reorganization (Fig. 2D) . EOG results of the four patients (III.1, IV.1, IV.2, IV.3) were normal, indicating that the function of the retinal pigment epithelium was normal and excluding this site as a possible origin of the macular dystrophy (data not shown). All ERG responses from IV.2, the proband’s clinically unaffected son, showed normal amplitudes and implicit times (Figs. 3A 3B 4) . Thus these normal responses negate any subclinical retinal dysfunction, which is in accordance with the absence of the H244R mutation in this family member. Implicit times of all the scotopic and photopic responses from affected persons (III.1, IV.1, IV.3) ranged within normal values. After dark adaptation, these patients had normal rod b-wave and mixed a- and b-wave amplitudes, indicating the absence of global dysfunctioning of the scotopic pathway (data not shown). Clinically, these patients had normal nocturnal vision and normal peripheral visual field vision, attesting that the global functioning of rod ON-BC was unaffected. After light adaptation, for each of these patients, the two first photopic OPs (OP2 and OP3) were barely recordable, whereas the third one (OP4) had normal amplitude values (Fig. 4) . Furthermore, for these patients cone a-wave amplitudes were normal, whereas cone b-waves amplitudes were moderately or severely decreased (Fig. 3A) . Flicker amplitudes were within normal range in patient IV.3, and they were decreased and severely decreased in patients IV.1 and III.1, respectively (Fig. 3B) . Together, these results suggest a defect in the visual signal transmission to the ON bipolar cells in the cone visual pathway only and a preserved global function of photoreceptors, outside the macula. 23 24  
Discussion
The H244R variant is of special interest because H244 is 100% conserved from flies to humans, and it is located in the functionally important CVC domain, which is essential, with the HD domain, for the repressive transcriptional action of VSX1. 25 In this report, H244R is associated with PPCD, macular dystrophy, and cone ON bipolar cell dysfunction, whereas the same variant has previously been identified in a familial case of keratoconus, highlighting that, despite the common molecular genetic etiology, the ocular phenotype in each family is variable. 17 Similarly, in a recent study, the P247R and G160D alleles of VSX1 were associated with keratoconus, whereas the same VSX1 variants in the series published by Héon et al. 26 were found to cosegregate with PPCD, inner retinal dysfunction, or both. Two genes are implicated in PPCD, but each of them accounts for the disease in only a small fraction of cases, indicating that other genes are probably involved. Although VSX1 allelic heterogeneity could explain in part the phenotypic variability observed in unrelated patients, it remains difficult to understand how persons with the same mutation can have different phenotypes and can even be asymptomatic carriers. However, this is common in a number of heritable forms of visual and hearing impairment, and it has been proposed that modifier genes or environmental interactions may obscure phenotype–genotype relationships by interacting in the same biologic pathway as the disease gene. 27 The availability of a second unrelated family, reported here, in which the H244R variant perfectly cosegregates with the disease phenotype, which is different from that previously described, reinforces the idea that H244R is a causative mutation and indicates that genetic modifiers might interfere with the pathologic effects of VSX1 variants by enhancing the phenotype or by reducing, or even suppressing, the effect of the mutant allele to the extent that it completely restores the normal condition. A noteworthy example of such a situation is provided by the spontaneous null allele for the CVC-homeobox Chx10 gene, closely related to Vsx1, which gives rise to an ocular retardation phenotype (or J ) in mice that can be partially restored depending on the genetic background. 14 28  
Numerous studies on OPs after pharmacologic synaptic blockages or in various human or mouse model retinal diseases in which the ON-BC pathway is compromised, with preservation of the OFF counterpart, have led to the concept that OP2 and OP3 are associated with the ON retinal pathway but that OP4 reflects the OFF pathway. 23 The ERG b-wave is elicited when glutamate release from photoreceptors is suppressed in response to light stimulation. In darkness, glutamate, continuously released by photoreceptors, hyperpolarizes ON-BC through the mGluR6-Go-protein complex, which is believed to be exclusively expressed by ON-BC. 24 29 In response to light stimulation, the cation channels that had been closed after activation of the mGluR6-Go-protein complex in darkness reopen, thereby depolarizing ON-BC. 29 30 31 Thus, absence or reduction of the b-wave amplitude is considered to reflect ON-BC dysfunctioning after light increment. The mGluR6- or Go-deficient mice fail to produce scotopic and photopic b-waves because of the absence of synaptic transmission from rods and cones to the ON bipolar cell pathway, resulting in the absence of depolarization of their ON-BC, mimicking darkness responses. 32 33 In the same way, the metabotropic glutamate agonist 2-amino-4-phosphonobutric acid (APB) selectively blocks the mGluR6 receptor on ON-BC and hyperpolarizes these cells by antagonizing their responses to light. APB produces ERG responses similar to those observed in mGluR6- or Go-deficient mice and induces a loss of OP2 and OP3 with a preserved OP4 amplitude. 24 34 35 Therefore, by analogy with all these models, we predict that our patients have a defective ON-BC pathway, leaving the OFF-bipolar circuitry relatively intact. Thus this study illustrates a selective dominant heritable cone ON-BC dysfunction that spares the OFF-BC circuitry and the scotopic pathway. These results are unusual because, as has been pointed out by Nelson and Connaughton, 36 the human disease processes or animal models that target the ON-BC pathway usually impair both the rod and the cone ON-BC and are always accompanied by a loss of nocturnal vision. The selective retinal defect present in this family could be explained by the restricted expression pattern of the Vsx1 gene, which is found in ON-BC and which has established input with cone photoreceptors only. 6 15 16 The electrophysiological results presented here differ from the published data on Vsx1 null mice and on VSX1 patients previously reported with cone OFF bipolar cell dysfunction and an abnormal scotopic bipolar cell pathway, respectively. 16 17 The explanation for this discrepancy is not clear and might be multifactorial. This discrepancy may reflect species differences or, alternatively, could depend on the nature of the Vsx1 mutation itself, which could have distinct molecular pathogenic mechanisms. Considering the existence of potential modifier genes for VSX1, a third possibility is that the genetic background of each person harboring a VSX1 missense mutation might contribute highly to the variable inner retinal dysfunction. 
To date, this is the first clinical report describing maculopathy associated with PPCD in patients with VSX1, highlighting a possible new alternative role of VSX1 in cone photoreceptors. Although the eye fundi of patients with VSX1 have been normal, subclinical macular impairment is suspected in some patients. 18 The assumption that VSX1 could play a role in cone biology is further reinforced by the fact that VSX1 transcript is found in the human WERI retinoblastoma cell line, which expresses cone-specific genes, and not in the Y-79 retinoblastoma cell line, which is rod-specific, leaving the possibility that VSX1 could play a role in the differentiation or maturation of cone photoreceptors. 8 Also supportive is that VSX1 is capable of binding in vitro to the core of the locus control region, which controls the expression of the red/green visual pigments indispensable for the maturation and viability of cone photoreceptors. 8 However, disease genes identified thus far as being implicated in inherited macular dystrophies have been shown to encode proteins that are expressed either in the photoreceptors or in the retinal pigment epithelium in which they exert specific roles. Recently, it has been shown that the human ABCR transcript, thought to be present in rods only, is in fact also expressed by foveal and peripheral cones, as has been found for its frog ortholog. 37 Vsx1 is absent in mature photoreceptors in all the species studied; however, in goldfish, Vsx1 is weakly expressed in a subset of undifferentiated proliferating neuroepithelial cells of the presumptive neural retina before it is repressed in retinal cells other than BCs when differentiation begins. 1 12 Because VSX1 functions as a transcriptional repressor and is repressed in a VSX1-dependent manner, one would predict that some specific mutations, notably those located in the CVC-domain of VSX1, could lead to aberrant or persistent expression of VSX1 in some retinal cells in which this gene is normally downregulated. Consequently, direct target genes of VSX1 would be upregulated, and a downregulator(s) of VSX1 could be temporally or spatially incorrectly activated, resulting in retinal defects. At present, this genetic pathologic mechanism is speculative, and the maculopathy observed in our patients remains unexplained. Further insight into the pathophysiology of VSX1 requires the development of a knock-in mouse carrying the H244R allele in the orthologous murine Vsx1 gene. 
 
Figure 1.
 
Pedigree of the family with the H244R mutation identified in the VSX1 gene. (A) Affected family members are drawn as closed circles (females) and closed squares (males), and unaffected family members are represented by open symbols. (Arrow) Proband. (B) Transmission electron microscopy of the corneal button from the proband revealed stratified pseudoepithelial cells with microvilli and desmosomal attachments (final magnification, ×7520). (C) Electrophoregram depicting the H244R mutation in exon 2 of the VSX1 gene from the proband’s DNA. (Arrowheads) Reverse and forward partial mutant sequences showing the A→G change.
Figure 1.
 
Pedigree of the family with the H244R mutation identified in the VSX1 gene. (A) Affected family members are drawn as closed circles (females) and closed squares (males), and unaffected family members are represented by open symbols. (Arrow) Proband. (B) Transmission electron microscopy of the corneal button from the proband revealed stratified pseudoepithelial cells with microvilli and desmosomal attachments (final magnification, ×7520). (C) Electrophoregram depicting the H244R mutation in exon 2 of the VSX1 gene from the proband’s DNA. (Arrowheads) Reverse and forward partial mutant sequences showing the A→G change.
Figure 2.
 
Aspects of patients’ eye fundi. (A) Fluorescein angiography images from the proband (III.1) aged 25. (B) Fluorescein angiography images from the proband (III.1) aged 45. (C) SLO of proband’s child (IV.1) showing the PRL inside the macular lesion. (D) SLO of proband’s child (IV.3) showing that PRL is located at the upper part of the macular lesion. (Arrows) Limits of the macular lesion.
Figure 2.
 
Aspects of patients’ eye fundi. (A) Fluorescein angiography images from the proband (III.1) aged 25. (B) Fluorescein angiography images from the proband (III.1) aged 45. (C) SLO of proband’s child (IV.1) showing the PRL inside the macular lesion. (D) SLO of proband’s child (IV.3) showing that PRL is located at the upper part of the macular lesion. (Arrows) Limits of the macular lesion.
Figure 3.
 
ERG recordings. (A) Photopic electroretinograms after adaptation to light. Proband’s unaffected child (IV.2) showed normal b-wave amplitude, whereas cone b-wave amplitude was decreased in the affected family members (III.1, IV.1, IV.3). (B) 30-Hz flicker electroretinogram recorded from the same family members.
Figure 3.
 
ERG recordings. (A) Photopic electroretinograms after adaptation to light. Proband’s unaffected child (IV.2) showed normal b-wave amplitude, whereas cone b-wave amplitude was decreased in the affected family members (III.1, IV.1, IV.3). (B) 30-Hz flicker electroretinogram recorded from the same family members.
Figure 4.
 
Cone-mediated OPs. In affected patients (III.1, IV.1, IV.3), OP2 and OP3 are markedly diminished to below the normal range, whereas OP4 amplitude is preserved. Normal OP pattern is shown in the unaffected child in this family (IV.2).
Figure 4.
 
Cone-mediated OPs. In affected patients (III.1, IV.1, IV.3), OP2 and OP3 are markedly diminished to below the normal range, whereas OP4 amplitude is preserved. Normal OP pattern is shown in the unaffected child in this family (IV.2).
LevineEM, HitchcockPF, GlasgowE, SchechterN. Restricted expression of a new paired-class homeobox gene in normal and regenerating adult goldfish retina. J Comp Neurol. 1994;348:596–606. [CrossRef] [PubMed]
LiuIS, ChenJD, PloderL, et al. Developmental expression of a novel murine homeobox gene (Chx10): evidence for roles in determination of the neuroretina and inner nuclear layer. Neuron. 1994;13:377–393. [CrossRef] [PubMed]
SvendsenPC, McGheeJD. The C. elegans neuronally expressed homeobox gene ceh-10 is closely related to genes expressed in the vertebrate eye. Development. 1995;121:1253–1262. [PubMed]
KurtzmanAL, GregoriL, HaasAL, SchechterN. Ubiquitination and degradation of the zebrafish paired-like homeobox protein VSX-1. J Neurochem. 2000;75:48–55. [PubMed]
ForresterWC, PerensE, ZallenJA, GarrigaG. Identification of Caenorhabditis elegans genes required for neuronal differentiation and migration. Genetics. 1998;148:151–165. [PubMed]
ChowRL, SnowB, NovakJ, et al. Vsx1, a rapidly evolving paired-like homeobox gene expressed in cone bipolar cells. Mech Dev. 2001;109:315–322. [CrossRef] [PubMed]
OhtoshiA, JusticeMJ, BehringerRR. Isolation and characterization of Vsx1, a novel mouse CVC paired-like homeobox gene expressed during embryogenesis and in the retina. Biochem Biophys Res Commun. 2001;286:133–140. [CrossRef] [PubMed]
HayashiT, HuangJ, DeebSS. RINX(VSX1), a novel homeobox gene expressed in the inner nuclear layer of the adult retina. Genomics. 2000;67:128–139. [CrossRef] [PubMed]
SeminaEV, Mintz-HittnerHA, MurrayJC. Isolation and characterization of a novel human paired-like homeodomain-containing transcription factor gene, VSX1, expressed in ocular tissues. Genomics. 2000;63:289–293. [CrossRef] [PubMed]
PassiniMA, KurtzmanAL, CangerAK, et al. Cloning of zebrafish vsx1: expression of a paired-like homeobox gene during CNS development. Dev Genet. 1998;23:128–141. [CrossRef] [PubMed]
PassiniMA, LevineEM, CangerAK, RaymondPA, SchechterN. Vsx-1 and Vsx-2: differential expression of two paired-like homeobox genes during zebrafish and goldfish retinogenesis. J Comp Neurol. 1997;388:495–505. [CrossRef] [PubMed]
LevineEM, PassiniM, HitchcockPF, GlasgowE, SchechterN. Vsx-1 and Vsx-2: two Chx10-like homeobox genes expressed in overlapping domains in the adult goldfish retina. J Comp Neurol. 1997;387:439–448. [CrossRef] [PubMed]
ChenCM, CepkoCL. Expression of Chx10 and Chx10–1 in the developing chicken retina. Mech Dev. 2000;90:293–297. [CrossRef] [PubMed]
BurmeisterM, NovakJ, LiangMY, et al. Ocular retardation mouse caused by Chx10 homeobox null allele: impaired retinal progenitor proliferation and bipolar cell differentiation. Nat Genet. 1996;12:376–384. [CrossRef] [PubMed]
OhtoshiA, WangSW, MaedaH, et al. Regulation of retinal cone bipolar cell differentiation and photopic vision by the CVC homeobox gene Vsx1. Curr Biol. 2004;14:530–536. [CrossRef] [PubMed]
ChowRL, VolgyiB, SzilardRK, et al. Control of late off-center cone bipolar cell differentiation and visual signaling by the homeobox gene Vsx1. Proc Natl Acad Sci USA. 2004;101:1754–1759. [CrossRef] [PubMed]
HeonE, GreenbergA, KoppKK, et al. VSX1: a gene for posterior polymorphous dystrophy and keratoconus. Hum Mol Genet. 2002;11:1029–1036. [CrossRef] [PubMed]
Mintz-HittnerHA, SeminaEV, FrishmanLJ, PragerTC, MurrayJC. VSX1 (RINX) mutation with craniofacial anomalies, empty sella, corneal endothelial changes, and abnormal retinal and auditory bipolar cells. Ophthalmology. 2004;111:828–836. [CrossRef] [PubMed]
BiswasS, MunierFL, YardleyJ, et al. Missense mutations in COL8A2, the gene encoding the alpha2 chain of type VIII collagen, cause two forms of corneal endothelial dystrophy. Hum Mol Genet. 2001;10:2415–2423. [CrossRef] [PubMed]
MarmorMF. Standardization notice: EOG standard reapproved electro-oculogram. Doc Ophthalmol. 1998;95:91–92. [CrossRef] [PubMed]
MarmorMF, ZrennerE. Standard for clinical electroretinography (1999 update): International Society for Clinical Electrophysiology of Vision. Doc Ophthalmol. 1998;97:143–156. [CrossRef] [PubMed]
SeminaEV, BrownellI, Mintz-HittnerHA, MurrayJC, JamrichM. Mutations in the human forkhead transcription factor FOXE3 associated with anterior segment ocular dysgenesis and cataracts. Hum Mol Genet. 2001;10:231–236. [CrossRef] [PubMed]
WachtmeisterL. Oscillatory potentials in the retina: what do they reveal. Prog Retin Eye Res. 1998;17:485–521. [CrossRef] [PubMed]
ChalupaLM, GunhanE. Development of on and off retinal pathways and retinogeniculate projections. Prog Retin Eye Res. 2004;23:31–51. [CrossRef] [PubMed]
DorvalKM, BobechkoBP, AhmadKF, BremnerR. Transcriptional activity of the paired-like homeodomain proteins Chx10 and Vsx1. J Biol Chem. 2005;280:10100–10108. [CrossRef] [PubMed]
BiscegliaL, CiaschettiM, De BonisP, et al. VSX1 mutational analysis in a series of Italian patients affected by keratoconus: detection of a novel mutation. Invest Ophthalmol Vis Sci. 2005;46:39–45. [CrossRef] [PubMed]
HaiderNB, IkedaA, NaggertJK, NishinaPM. Genetic modifiers of vision and hearing. Hum Mol Genet. 2002;11:1195–1206. [CrossRef] [PubMed]
Bone-LarsonC, BasuS, RadelJD, et al. Partial rescue of the ocular retardation phenotype by genetic modifiers. J Neurobiol. 2000;42:232–247. [CrossRef] [PubMed]
NawyS. Regulation of the on bipolar cell mGluR6 pathway by Ca2+. J Neurosci. 2000;20:4471–4479. [PubMed]
DhingraA, LyubarskyA, JiangM, et al. The light response of ON bipolar neurons requires G[alpha]o. J Neurosci. 2000;20:9053–9058. [PubMed]
ShiellsRA, FalkG. A rise in intracellular Ca2+ underlies light adaptation in dogfish retinal ‘on’ bipolar cells. J Physiol. 1999;514:343–350. [CrossRef] [PubMed]
TakaoM, MorigiwaK, SasakiH, et al. Impaired behavioral suppression by light in metabotropic glutamate receptor subtype 6-deficient mice. Neuroscience. 2000;97:779–787. [CrossRef] [PubMed]
MasuM, IwakabeH, TagawaY, et al. Specific deficit of the ON response in visual transmission by targeted disruption of the mGluR6 gene. Cell. 1995;80:757–765. [CrossRef] [PubMed]
DolanRP, SchillerPH. Effects of ON channel blockade with 2-amino-4-phosphonobutyrate (APB) on brightness and contrast perception in monkeys. Vis Neurosci. 1994;11:23–32. [CrossRef] [PubMed]
NakajimaY, IwakabeH, AkazawaC, et al. Molecular characterization of a novel retinal metabotropic glutamate receptor mGluR6 with a high agonist selectivity for L-2-amino-4-phosphonobutyrate. J Biol Chem. 1993;268:11868–11873. [PubMed]
NelsonR, ConnaughtonV. Bipolar cell pathways in the vertebrate retina. ;Available at: . Accessed October 27, 2005.
MoldayLL, RabinAR, MoldayRS. ABCR expression in foveal cone photoreceptors and its role in stargardt macular dystrophy (Abstract). Am J Ophthalmol. 2000;130:689.
Figure 1.
 
Pedigree of the family with the H244R mutation identified in the VSX1 gene. (A) Affected family members are drawn as closed circles (females) and closed squares (males), and unaffected family members are represented by open symbols. (Arrow) Proband. (B) Transmission electron microscopy of the corneal button from the proband revealed stratified pseudoepithelial cells with microvilli and desmosomal attachments (final magnification, ×7520). (C) Electrophoregram depicting the H244R mutation in exon 2 of the VSX1 gene from the proband’s DNA. (Arrowheads) Reverse and forward partial mutant sequences showing the A→G change.
Figure 1.
 
Pedigree of the family with the H244R mutation identified in the VSX1 gene. (A) Affected family members are drawn as closed circles (females) and closed squares (males), and unaffected family members are represented by open symbols. (Arrow) Proband. (B) Transmission electron microscopy of the corneal button from the proband revealed stratified pseudoepithelial cells with microvilli and desmosomal attachments (final magnification, ×7520). (C) Electrophoregram depicting the H244R mutation in exon 2 of the VSX1 gene from the proband’s DNA. (Arrowheads) Reverse and forward partial mutant sequences showing the A→G change.
Figure 2.
 
Aspects of patients’ eye fundi. (A) Fluorescein angiography images from the proband (III.1) aged 25. (B) Fluorescein angiography images from the proband (III.1) aged 45. (C) SLO of proband’s child (IV.1) showing the PRL inside the macular lesion. (D) SLO of proband’s child (IV.3) showing that PRL is located at the upper part of the macular lesion. (Arrows) Limits of the macular lesion.
Figure 2.
 
Aspects of patients’ eye fundi. (A) Fluorescein angiography images from the proband (III.1) aged 25. (B) Fluorescein angiography images from the proband (III.1) aged 45. (C) SLO of proband’s child (IV.1) showing the PRL inside the macular lesion. (D) SLO of proband’s child (IV.3) showing that PRL is located at the upper part of the macular lesion. (Arrows) Limits of the macular lesion.
Figure 3.
 
ERG recordings. (A) Photopic electroretinograms after adaptation to light. Proband’s unaffected child (IV.2) showed normal b-wave amplitude, whereas cone b-wave amplitude was decreased in the affected family members (III.1, IV.1, IV.3). (B) 30-Hz flicker electroretinogram recorded from the same family members.
Figure 3.
 
ERG recordings. (A) Photopic electroretinograms after adaptation to light. Proband’s unaffected child (IV.2) showed normal b-wave amplitude, whereas cone b-wave amplitude was decreased in the affected family members (III.1, IV.1, IV.3). (B) 30-Hz flicker electroretinogram recorded from the same family members.
Figure 4.
 
Cone-mediated OPs. In affected patients (III.1, IV.1, IV.3), OP2 and OP3 are markedly diminished to below the normal range, whereas OP4 amplitude is preserved. Normal OP pattern is shown in the unaffected child in this family (IV.2).
Figure 4.
 
Cone-mediated OPs. In affected patients (III.1, IV.1, IV.3), OP2 and OP3 are markedly diminished to below the normal range, whereas OP4 amplitude is preserved. Normal OP pattern is shown in the unaffected child in this family (IV.2).
×
×

This PDF is available to Subscribers Only

Sign in or purchase a subscription to access this content. ×

You must be signed into an individual account to use this feature.

×