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EGFLAM Pathogenic Variants and Congenital Stationary Night Blindness.

IMPORTANCE: Congenital stationary night blindness (CSNB) is a clinically and genetically heterogeneous inherited retinal disorder (IRD), and in many complete CSNB (cCSNB) cases, the underlying genetic cause remains unknown. Uncovering the genetic defects of IRDs helps to refine diagnostic methods and supports the development of specific therapeutic approaches. OBJECTIVE: To describe the phenotype and the underlying gene defect in patients with cCSNB from 2 unrelated families. DESIGN, SETTING AND PARTICIPANTS: This retrospective case series was conducted from January 2023 to July 2025. Data for 3 patients from cohorts of genetically unsolved IRD cases in France (n = 140 for CSNB) and the Netherlands (n = 2730 for IRD) were analyzed clinically and genetically. EXPOSURES: Complete ocular examination, including multimodal retinal imaging and full-field electroretinography (ffERG) incorporating the International Society for Clinical Electrophysiology of Vision standards and multimodal retinal imaging, were performed. Gene defects were identified by genome sequencing (GS) and exome sequencing (ES). MAIN OUTCOMES AND MEASURES: The main outcome was a gene defect, EGFLAM, underlying cCSNB. Measures included phenotyping, GS, ES, Sanger sequencing, and cosegregation analysis. RESULTS: The series included 3 patients from 2 unrelated families of Moroccan ancestry showing high myopia, reduced visual acuity, and night blindness. Retinal imaging depicted myopic changes. ffERG revealed electronegative Schubert-Bornschein configuration in keeping with cCSNB with ON-bipolar cell dysfunction. Patients were lacking pathogenic variants in known genes implicated in IRDs, including CSNB. Two different homozygous pathogenic variants, c.1563_1566del, p.(Val522Glufs*18) and c.1795C>T, p.(Arg599*) in EGFLAM were identified by ES and GS. The corresponding protein is localized in the outer plexiform layer and important for ON-bipolar cell signaling in the retina. CONCLUSION AND RELEVANCE: This case series reports on a gene defect in EGFLAM implicated in human cCSNB. Clinicians should be aware about this association and consider including EGFLAM in diagnostic gene panels for IRDs. This discovery may lead to faster and more accurate diagnosis of cCSNB and genetic counseling, as well as a pathway for developing therapies.

Adolescent

Linkage analysis in X-linked congenital stationary night blindness.

X-linked congenital stationary night blindness (XL-CSNB) is a nonprogressive disorder of the retina, characterized by night blindness, reduced visual acuity, and myopia. Previous studies have localized the CSNB1 locus to the region between OTC and TIMP on the short arm of the X chromosome. We have carried out linkage studies in three XL-CSNB families that could not be classified as either complete or incomplete CSNB on the criteria suggested by Miyake et al. (1986. Arch. Ophthalmol. 104: 1013-1020). We used markers for the DXS538, DMD, OTC, MAOA, DXS426, and TIMP loci. Two-point analyses show that there is close linkage between CSNB and MAOA (theta max = 0.05, Zmax = 3.39), DXS426 (theta max = 0.06, Zmax = 2.42), and TIMP (theta max = 0.07, Zmax = 2.04). Two multiply informative crossovers are consistent with CSNB lying proximal to MAOA and distal to DXS426, respectively. Multipoint analysis supports this localization, giving the most likely order as DMD-17 cM-MAOA-7.5 cM-CSNB-7.5 cM-DXS426/TIMP-cen, and thus refines the localization of CSNB.

Female

Affected females in X-linked congenital stationary night blindness.

Most heterozygous (carrier) females in families with X-linked congenital stationary night blindness are asymptomatic. Several anecdotal cases of manifesting females in X-linked congenital stationary night blindness have been reported, but few clinical details are available. The authors report clinical, electroretinographic, and dark adaptation studies of four affected females from a five-generation family with X-linked congenital stationary night blindness. Each of the manifesting females was the daughter of a different, asymptomatic, carrier mother. None of the 14 daughters of the 9 affected males showed signs or symptoms of congenital stationary night blindness. Uneven X-chromosomal lyonization is the most likely reason for these females manifesting this X-linked disorder.

Adolescent

'On' response defect in paraneoplastic night blindness with cutaneous malignant melanoma.

Response properties of rod and cone systems were assessed in a patient with an acquired form of night blindness associated with a metastatic cutaneous malignant melanoma. The night blindness, a sensation of shimmering lights, and selective reductions in the amplitudes of both rod and cone electroretinographic (ERG) b-waves were present before and after chemotherapy, confirming that this disorder was a paraneoplastic consequence of the melanoma rather than a response to chemotherapy. During ERG testing with flashes of extended duration, the cone b-wave abnormality was found to be a predominant loss of the cone ERG "on" response with relative preservation of the "off" response, similar to that observed in patients with congenital stationary night blindness. An impairment in signal transmission specific for retinal "on" pathways may be a primary defect in both of these forms of night blindness.

Adolescent

Ultrastructural changes of the retina and the retinal pigment epithelium in Briard dogs with hereditary congenital night blindness and partial day blindness.

The offspring of two Briard dogs (brother and sister) with congenital, clinically stationary night blindness showed an aggravation of the disease with severe impairment of day vision in addition to night blindness. This ultrastructural study was performed on four such second generation puppies at the age of 4 months. The neuroretina and retinal pigment epithelium (RPE) from four locations were studied: the central area (immediately temporal to the optic disc); the centre of the tapetal area; the upper periphery (border of tapetal area); and the lower periphery (non-tapetal area). The RPE showed large inclusions, seemingly lipid in nature, mainly in the central and tapetal areas of the retina. Small, membrane bound, electron-dense inclusions were scattered in the RPE cytoplasm in all areas examined. The small inclusions were found to be less numerous in normal than in affected dogs and may be lysosomal in nature. Forty to fifty percent of the rod outer segments in the tapetal area showed disorientation of the disc membranes, whereas the corresponding figures were 20-40% in the central and lower peripheral areas and 6-25% in the upper peripheral area. No structural abnormalities were found in the rod inner segments or synaptic bodies. The cones were better preserved. The inner retina appeared normal. These electron microscopic findings seem to correspond to a previously published electrophysiologic evaluation, indicating a defective and delayed rod function (virtually no scotopic a- and b-waves), a better preserved cone function (photopic flicker responses present, although reduced) and impaired RPE activity (a prominent, slow negative potential of long latency at the site of the c-wave). It appears that these Briard dogs, showing structural changes of the rod outer segments in addition to pigment epithelial inclusions, mainly located in the posterior pole, comprise a pigment epitheliopathy and retinopathy morphologically different from other hereditary canine retinopathies that have been described earlier in the literature and different from animal models of congenital night blindness.

Animals

Changes in the DC electroretinogram in Briard dogs with hereditary congenital night blindness and partial day blindness.

Five Briard dogs, 7-12 months old, with congenital night blindness and severely reduced day vision (offspring of a sister and brother with congenital and supposedly stationary night blindness but with normal or nearly normal day vision) and three normal control dogs were studied by means of direct current (DC) electroretinography in order to analyse fast and slow retinal and pigment epithelial (RPE) potentials. No definite a- and b-waves were seen in the affected dogs in the dark-adapted state, which indicates severely impaired rod function. All affected dogs responded to 30 Hz flickering light in the light-adapted state, although with an amplitude reduced by 50-70%. Thus, cone function was better preserved than rod function. The control dogs showed a small c-wave and a deep negative trough between the b- and c-waves, indicating that slow PIII from the Müller cells, as well as the photoreceptor potential, are very prominent. In the affected dogs, there was no c-wave, but from a stimulus intensity of 3 log U above the normal b-wave threshold, a slow negative potential appeared, the latency and peak time of which were very long, 5-7 and 11-15 sec, respectively. With increasing stimulus intensities, both parameters decreased substantially, whereas the amplitude increased to a maximum of 2400 microV. In the light-adapted state, the dog with the best day vision showed a negative potential of short duration (peak time about 0.2 sec), followed by a positive potential (peak time about 1.2 sec).(ABSTRACT TRUNCATED AT 250 WORDS)

Animals

[Family investigation and clinical genetic analysis of a large pedigree with congenital stationary night blindness].

A large pedigree of congenital stationary night blindness (CSNB) was investigated by both the family method and the family history method, and the diagnosis was confirmed by dark adaptation and full-field electroretinogram tests. There were 57 affected members of 7 successive generations in the pedigree which showed typical autosomal dominant inheritance with a complete gene penetrance. Based on this study and other sources, the genetic aspect and the clinical manifestations of CSNB, especially the characteristics of dark adaptation and electroretinogram, were discussed.

Adult

Paradoxical pupillary responses in congenital stationary night blindness.

Three unrelated boys, ages 2, 6, and 10 years, who have congenital stationary night blindness with myopia and a Schubert-Bornschein-type electroretinogram finding, were found to show a "paradoxical" pupillary constriction in darkness. When examining room lights are turned out, the patient's pupils briskly constrict and slowly dilate. Older night blind male relatives of these boys did not show this abnormal constriction to darkness.

Adolescent

Correlation of clinicopathologic findings in a patient. Congenital night blindness, branch retinal vein occlusion, cilioretinal artery, drusen of the optic nerve head, and intraretinal pigmented lesion.

The ocular clinicopathologic features of this unique patient were congenital stationary night blindness, drusen of the optic nerve head, cilioretinal artery, intraretinal pigmented lesion, and branch retinal vein occlusion. Photocoagulation therapy led to total disappearance of the neovascular tissue, clinically and histopathologically. Histopathologic examination showed an occluded branch vein associated with a sclerotic retinal arteriole. Peripheral to the site of venous occlusion, inner ischemic retinal atrophy was present. The normal complement of rod and cone photoreceptors supports the view that the night blindness in this case was an abnormality in the neural transmission and not on a morphological basis. The pigmented intraretinal lesion proved to be a localized area of retinal and choroidal neovascularization with anastomosis and secondary retinal pigment epithelial hyperplasia. This lesion was identical to Fuchs' dot of myopia but out patient was hyperopic.

Argon

Anesthetically blocked optic nerve conduction in congenital stationary night blindness.

It has been hypothesized that the negative configuration of the electroretinogram (ERG) in congenital stationary night blindness (CSNB) may change to a positive configuration following loss of the inhibitory function of the optic nerve centrifugal fibers. In order to study this hypothesis, the ERGs before and after blocking optic nerve conduction by retrobulbar anesthesia were recorded in a patient with CSNB, who had retinal breaks and was being treated with cryopexy under retrobulbar anesthesia. After complete blockade of the optic nerve conduction induced by retrobulbar anesthesia, the ERG showed little change in comparison with that recorded before anesthesia. The above finding indicates that the temporary blockade of optic nerve conduction does not modify the ERG configuration in CSNB.

Anesthesia, Local

A Japanese pedigree of autosomal dominant congenital stationary night blindness with variable expressivity.

Three cases in three successive generations of one family with autosomal dominant congenital stationary night blindness are presented. Case 1, the proband, and Case 3, his grandfather had the same electroretinographic responses: nonrecordable scotopic electroretinogram (ERG), normal but slightly diminished flicker ERG, and negative-shaped single bright-flash ERG. Their dark adaptation curves were monophasic with no rod segment. However, Case 2, the proband's father, showed different ERG findings; a moderately diminished scotopic ERG, a normal flicker ERG, and a biphasic dark adaptation curve with an elevated final rod threshold. The authors believe that these differences reflect variations in the expressivity of a single gene mutation with the lowest expressivity being seen in Case 2.

Adult

Mapping of locus for X-linked congenital stationary night blindness (CSNB1) proximal to DXS7.

A recombinant chromosome in a male affected with X-linked congenital stationary night blindness (CSNB1) provides new information on the location of the CSNB1 locus. A four-generation family with five males affected with X-linked CSNB was analyzed with five polymorphic markers for four X-chromosome loci spanning the region OTC (Xp21.1) to DXS255 (Xp11.22). Four of the males inherited the same X chromosome; one male inherited a chromosome that from OTC to DXS7, inclusive, was derived from the normal X chromosome of his unaffected grandfather and that from a location between DXS7 and DXS426 proximally was derived from the chromosome carrying the CSNB1 locus. This recombinant maps the CSNB1 locus in this family to a region on the short arm of the X chromosome proximal to the DXS7 locus.

Alleles

Autosomal dominant stationary night-blindness. A large family rediscovered.

In 1909, 2 years after the famous publication by Nettleship, a large family with congenital stationary night-blindness of the 'Nougaret type' was published by the Danish district surgeon, Sigurd Rambusch. In 1990 the 'Rambusch family', still resident in the original area, was sought out and rediscovered, at which time the reconstructed part of the pedigree comprised more than 200 affected persons in 11 generations. Dark adaptometry and electroretinography were performed on a few affected family members, including a descendant with a uniocular affection. The pedigree is presented and recordings of dark adaptation courses and electroretinographical responses from a few family members are demonstrated.

Adult

Congenital stationary night blindness: an animal model.

Electroretinographic studies of myctalopic Appaloosa horses demonstrated photopic and scotopic abnormalities similar to those in humans with congenital stationary night blindness (CSNB) of the Schubert-Bornschein type. The phototopic abnormalities consisted of reduced b-wave amplitudes and slower than normal b-wave implict time. The dark-adapted ERG's consisted of a simple negative potential; the scotopic b-wave was nonrecordable. However, a normal c-wave was present in the dark-adapted response. Histologic studies demonstrated no structural abnormalities that could explain the functional defect.

Adaptation, Physiological

An image intensifier aid for chronic night blindness.

Working with the Retinitis Pigmentosa Foundation, ITT has designed an image intensifier monocular specifically for application as a prosthetic aid for persons suffering from chronic night blindness as a result of retinal degenerations. A description of the instrument along with the rationale for its major design points is given and its applications illustrated. The first few of these instruments were delivered earlier this year and limited production has been started.

Humans

Night blindness and the retinal mechanism of visual adaptation.

An account is given of investigations into the mechanisms of dark-adaptation in the retina of man and of the skate and other fish. Working hypotheses as to the possible sites of abnormal function in the various disorders of which night blindness is a feature are presented.

Animals

Night blindness, characteristic facies, and skeletal abnormalities in two brothers.

Two brothers are described with a similar physical appearance characterised by minor periorbital anomalies, malar flatness, a maxillary overbite, retrognathia, sloping shoulders, joint hyperextensibility, and minor radiological anomalies. In addition, they had a slowly progressing night blindness, myopia, and extinguished electroretinograms. The mother had mild expression of some of the physical anomalies and a decreased electroretinogram response to red light. We have been unable to find any report of similarly affected children. The possible modes of inheritance are discussed.

Abnormalities, Multiple