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 Table of Contents  
CASE REPORT
Year : 2022  |  Volume : 2  |  Issue : 1  |  Page : 136-139

Analysis of microstructural changes in an X-linked juvenile retinoschisis patient harboring RS1 G668A mutation by en-face optical coherence tomography imaging


1 Department of Vitreo-Retina Services, Aravind Eye Hospital, Madurai, Tamil Nadu, India
2 Department of Genetics, Aravind Medical Research Foundation, Madurai, Tamil Nadu, India
3 Department of Genetics, Aravind Medical Research Foundation, Madurai; Department of Molecular Biology, Aravind Medical Research Foundation - Affiliated to Alagappa University, Karaikudi, Tamil Nadu, India
4 Department of Paediatric Ophthalmology and Adult Strabismus Services, Aravind Eye Hospital, Madurai, Tamil Nadu, India

Date of Submission17-May-2021
Date of Acceptance29-Jun-2021
Date of Web Publication07-Jan-2022

Correspondence Address:
Dr. Periasamy Sundaresan
Department of Genetics, Aravind Medical Research Foundation, 1, Anna Nagar, Madurai - 625 020, Tamil Nadu
India
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Source of Support: None, Conflict of Interest: None


DOI: 10.4103/ijo.IJO_1283_21

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  Abstract 


Juvenile X-linked retinoschisis (JXLR) is an X-linked recessive retinal dystrophy caused by retinoschisin (RS1) gene mutations. The current study reports and describes the cumulative findings of en-face OCT for a 7-year-old JXLR patient harboring a hemizygous pathogenic RS1 mutation (c.G668A; p.Cys223Tyr), where residue 223 is vital for cellular adhesion. Fundoscopy showed cart-wheel appearance at macula. Further, en-face OCT revealed characteristic schitic lesions in the ganglion cell layer, inner plexiform layer, inner nuclear layer, and outer plexiform layer. Our report adds to the Indian RS1 mutation spectrum and casts insights into the schisis microstructure using en-face imaging.

Keywords: Cys223Tyr, en-face OCT, India, Retinoschisis, RS1


How to cite this article:
Mishra C, Duvesh R, Chowdhury S, Anjanamurthy R, Kannan NB, Ramasamy K, Sundaresan P. Analysis of microstructural changes in an X-linked juvenile retinoschisis patient harboring RS1 G668A mutation by en-face optical coherence tomography imaging. Indian J Ophthalmol Case Rep 2022;2:136-9

How to cite this URL:
Mishra C, Duvesh R, Chowdhury S, Anjanamurthy R, Kannan NB, Ramasamy K, Sundaresan P. Analysis of microstructural changes in an X-linked juvenile retinoschisis patient harboring RS1 G668A mutation by en-face optical coherence tomography imaging. Indian J Ophthalmol Case Rep [serial online] 2022 [cited 2022 Jan 19];2:136-9. Available from: https://www.ijoreports.in/text.asp?2022/2/1/136/334865

Chitaranjan Mishra, Roopam Duvesh; First two authors equal contribution




Juvenile X-linked retinoschisis (JXLR, OMIM 312700) is an inherited retinal degenerative disease which primarily affects males in an X-linked recessive manner.[1] Classically, it is associated with early vision impairment in first decade of life.[1] It is characterized by the foveal schisis resulting from inner retinal layer splitting, thus represents an archetypal spoke-wheel appearance and a negative electroretinogram (ERG) because of reduced b-wave amplitude.[1],[2]

The candidate gene underlying JXLR pathogenesis is RS1 (chromosome Xp22.2), comprising of six exons.[1],[2],[3] It encodes an adhesive 24kDa retinoschisin protein secreted from photoreceptors and bipolar cells.[1],[2],[3] Retinoschisin is reported to involve in cellular adhesion and cell–cell interactions, thus maintains the structural and functional integrity of the retina.[1],[2],[3] Hence, mutations leading to faulty retinoschisin protein might reduce the adhesion across retinal layers resulting into schisis formation. So far, more than 300 unique variants of the RS1 gene have been reported, which are documented in the databases including Leiden Open Variation Database (https://databases.lovd.nl/shared/genes/RS1; Leiden Open Variation Database, LOVD v. 3.0 Build 26c). However, a few studies from India have reported RS1 mutations associated with X-linked retinoschisis till now, which include missense, nonsense, deletions, duplications, frameshifts, and splice site mutations.[4],[5],[6],[7]

With the help of optical coherence tomography (OCT), studies have demonstrated splitting in the foveomacular region involving different retinal layers in JXLR.[8],[9] In the last few years, en-face imaging has helped to visualize different patterns of retinoschisis, namely, spoke-like pattern, reticular, and polygonal pattern.[10] Herein, the present study describes the detailed combinatorial findings of en-face OCT imaging and RS1 mutation status for an Indian JXLR patient.


  Case Report Top


A 7-year-old male child born to nonconsanguineous parents was presented to our hospital due to decrease in visual acuity. On ophthalmic examinations of both the eyes, his best-corrected distant vision was 6/24 and near vision was N-6. Anterior segments were normal for both the eyes. Fundoscopic assessments (Zeiss fundus camera) revealed cart-wheel appearance at the macula due to foveal schisis [Figure 1]a, [Figure 1]b which was also documented through spectral-domain-OCT (Spectralis Heidelberg Engineering Inc., Vista, CA, USA) [Figure 1]c, [Figure 1]d consistent with JXLR phenotype. Other findings like peripheral retinoschisis, retinal detachment, vitreous hemorrhage, and proliferative vitreoretinopathy changes were absent. Confocal scanning laser ophthalmoscopy blue light fundus autofluorescence image showed mild hypo-autofluorescence at the center of fovea in both the eyes, similar to the FAF of fovea for a healthy subject of the same age and gender [Figure 1]e, [Figure 1]f. The en-face OCT imaging through the retinal nerve fiber (RNFL) layer did not show any schitic lesions [Figure 2]a, [Figure 2]b. However, the images taken through the ganglion cell layer (GCL), [Figure 2]c, [Figure 2]d, inner plexiform layer, inner nuclear layer (INL) and outer plexiform layer (OPL) [Figure 2]e, [Figure 2]f were suggestive of characteristic spoke-like schitic lesions. There were no peripheral retinoschisis or any other fundus abnormalities were observed. In both the eyes, there was reduction in the “b” wave amplitudes with larger “a” waves, suggestive of negative ERG, a key diagnostic finding in JXLR [Figure 3]a as compared to a normal subject with larger “b” wave amplitude [Figure 3]b.
Figure 1: Patient's clinical findings, where images on the left-side panel denotes the right eye and right-side panel for the left eye. (a, b) Fundus photo of both the eyes for the JXLR patient showing spoke-wheel or cart-wheel appearance at the macula due to foveal schisis. (c, d) Optical coherence tomography (OCT) images showing foveal schisis in both the eyes. OCT B scan was taken passing through the center of the fovea and 8.9 mm in length. (e, f) Confocal scanning laser ophthalmoscopy (cSLO) blue light fundus autofluorescence (FAF) image showing reduced FAF signal in the macular area. [Color fundus imaging – Zeiss fundus camera; SD-OCT – Spectralis Heidelberg Engineering Inc., Vista, CA, USA]

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Figure 2: An en-face OCT image of the patient at the level of the (a, b) retinal nerve fiber layer (RNFL) of the RE and the LE, respectively; (c, d) ganglion cell layer (GCL) of the RE and the LE, respectively; (e, f) inner plexiform layer (IPL) – outer plexiform layer (OPL) layer complex of the RE and the LE, respectively. Left panel of each image represents the OCT B scan. Please note that the two dashed red lines (also indicated by the red and yellow arrows) indicate the layers of the retina, where the segmentation was done manually. The middle panel of the images represent the en-face structural slab. No definite schitic pattern in RNFL layers was observed. In the GCL, spoke-like pattern in the foveal region was observed. In IPL-OPL layers, there is a spoke-like pattern in the foveal as well as the perifoveal regions. The right panel of the images represent the OCTA flow signal

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Figure 3: Representative full-field electroretinogram (ff-ERG) images. (a) Dark adapted 10 ERG (strong flash ERG, combined response) of the patient showing reduction in the “b” wave amplitudes with larger “a” waves suggestive of negative ERG in both the eyes. (b) Representative ERG from age-matched normal subject indicating normal “a” and “b” waves. [ERG recorded as per International Society for Clinical Electrophysiology of Vision (ISCEV) standards

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For genetic analysis, polymerase chain reaction for all six exons of RS1 was performed using published primers and conditions[4] followed by Sanger sequencing (ABI 3500 Genetic analyzer, Applied Biosystems, CA). A hemizygous missense mutation c.G668A (p.Cys223Tyr) at the end of exon 6 was identified in the patient [Figure 4]a, [Figure 4]b. Segregation analysis revealed heterozygous mutation in the patient's mother, while father had wild-type genotype [Figure 4]b, corroborating X-linked inheritance. In silico tools (SIFT, PolyPhen2 and Mutation Taster) predicted this mutation as probably deleterious. Evolutionary conservation analysis across different species showed highly conserved nature of this codon position [Figure 4]c.
Figure 4: (a) Schematic representation of RS1 gene structure and encoded protein domains. Location of 10 cysteine (Cys) residues of retinoschisin protein are marked in brown color. Purple color boxes show the distribution of RS1 mutations from Indian JXLR patients reported so far. Pink color box highlighted the mutation identified in the current study (C223Y) [NM_000330.3:c.668G>A; NP_000321.1:p.Cys223Tyr]. (b) Pedigree showing male patient affected by JXLR disease (filled black symbols with arrow-termed as Proband) and white unfilled square symbol indicate unaffected male. Circle with dot in center represents carrier female (mother). No consanguinity seen between parents. Sequencing electropherograms of the patient showed hemizygosity for RS1 mutation c.G668A, heterozygous carrier mother and father with normal genotype, and consistent with X-linked recessive inheritance for JXLR disease. (c) Evolutionary conservation analysis using multiple sequence alignment tool (CLUSTAL O (1.2.4)) showed conservation of the amino acid at codon position 223 (indicated by arrow) across different species. Sibling sample was not available for genetic testing

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  Discussion Top


Herein, the present report illustrates the collective findings of en-face OCT and RS1 mutation screening for a JXLR patient. His fundoscopic assessments revealed cart-wheel appearance at the macula, which is a native finding seen in JXLR patients. To gain further acumens into the systematic architecture of schisis formations in the patient, en-face OCT scans were performed across different retinal layers. We observed typical spoke-like pattern in the GCL, INL and OPL; a finding similar to a prior report.[10] The probable reasons for absence of schitic cavities in the RNFL or ONL layers may be the rare occurrence of cavities in these layers, especially in young patients. In our patient, we could see faint hyporeflective lesions in the RNFL layer on OCTA bilaterally, not amounting to typical schitic cavities. These lesions may develop to schitic cavities over a period of time, which needs a longer follow-up and serial documentations. Notably, gene therapy trials for XLRS are underway which involves monitoring of patient's retinal morphology.[11] Moreover, extent of schitic cavities and detailed microstructural changes can be supervised by en-face OCT imaging to gain profound knowledge, useful for clinical considerations with regard to ongoing trials for retinoschisis.

RS1 mutational screening identified a pathogenic mutation Cys223Tyr belonging to c-terminal region of the retinoschisin, which substitutes amino acid cysteine (Cys) at position 223 to tyrosine (Tyr). Cys residues are vital in maintaining RS1 homo-octameric complex and retinal structure integrity, especially residues at positions 59 and 223 which mediates the intermolecular disulfide bonding.[1],[3] Thus, substitution of cysteine by bulkier tyrosine breaks disulfide linkage, affecting protein stability and conformation. Though this mutation was first detected in 2010[12]; yet, it has not been reported so far from India. Nevertheless, this is a single case report; future studies comprising more patients with longer follow-ups will help in better understanding of the morphology and pattern of schitic cavities over time.


  Conclusion Top


This study highlights the importance of en-face imaging toward understanding of schisis microstructure. Additionally, this report adds to the spectrum of RS1 mutations list from India and aid in carrier status determination for further genetic counseling.

Acknowledgements

We thank the patient and family members for their participation in the study. We also thank Aravind Eye Care System for the support. We also acknowledge Lady Tata Memorial Trust for the award of research scholarship to Ms. Susmita Chowdhury.

Ethics statement

This study was approved by the Institutional Ethics Committee and adhered to the tenets of Declaration of Helsinki. Written informed consent were obtained from all the study participants.

Declaration of patient consent

The authors certify that they have obtained all appropriate patient consent forms. In the form the patient(s) has/have given his/her/their consent for his/her/their images and other clinical information to be reported in the journal. The patients understand that their names and initials will not be published and due efforts will be made to conceal their identity, but anonymity cannot be guaranteed.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.



 
  References Top

1.
Wu WWH, Molday RS. Defective discoidin domain structure, subunit assembly, and endoplasmic reticulum processing of retinoschisin are primary mechanisms responsible for X-linked retinoschisis. J Biol Chem 2003;278:28139-46.  Back to cited text no. 1
    
2.
Molday RS, Kellner U, Weber BHF. X-linked juvenile retinoschisis: Clinical diagnosis, genetic analysis, and molecular mechanisms. Prog Retin Eye Res 2012;31:195-212.  Back to cited text no. 2
    
3.
Wu WWH, Wong JP, Kast J, Molday RS. RS1, a discoidin domain-containing retinal cell adhesion protein associated with X-linked retinoschisis, exists as a novel disulfide-linked octamer. J Biol Chem 2005;280:10721-30.  Back to cited text no. 3
    
4.
Suganthalakshmi B, Shukla D, Rajendran A, Kim R, Nallathambi J, Sundaresan P. Genetic variations in the hotspot region of RS1 gene in Indian patients with juvenile X-linked retinoschisis. Mol Vis 2007;13:611-7.  Back to cited text no. 4
    
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Shukla D, Rajendran A, Gibbs D, Suganthalakshmi B, Zhang K, Sundaresan P. Unusual manifestations of x-linked retinoschisis: Clinical profile and diagnostic evaluation. Am J Ophthalmol 2007;144:419-23.  Back to cited text no. 5
    
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Sudha D, Neriyanuri S, Sachidanandam R, Natarajan SN, Gandra M, Tharigopala A, et al. Understanding variable disease severity in X-linked retinoschisis: Does RS1 secretory mechanism determine disease severity? PLoS One 2018;13:e0198086.  Back to cited text no. 6
    
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Selvan H, Sharma A, Birla S, Gupta S, Somarajan BI, Gupta V, et al. Molecular characterization of a rare phenotype of X-linked retinoschisis with angle-closure glaucoma. Indian J Ophthalmol 2019;67:1226-9.  Back to cited text no. 7
[PUBMED]  [Full text]  
8.
Gregori NZ, Berrocal AM, Gregori G, Murray TG, Knighton RW, Flynn HW, et al. Macular spectral-domain optical coherence tomography in patients with X linked retinoschisis. Br J Ophthalmol 2009;93:373-8.  Back to cited text no. 8
    
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Yu J, Ni Y, Keane PA, Jiang C, Wang W, Xu G. Foveomacular schisis in juvenile X-linked retinoschisis: An optical coherence tomography study. Am J Ophthalmol 2010;149:973-8.e2.  Back to cited text no. 9
    
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Yoshida-Uemura T, Katagiri S, Yokoi T, Nishina S, Azuma N. Different foveal schisis patterns in each retinal layer in eyes with hereditary juvenile retinoschisis evaluated by en-face optical coherence tomography. Graefes Arch Clin Exp Ophthalmol 2017;255:719-23.  Back to cited text no. 10
    
11.
Cukras C, Wiley HE, Jeffrey BG, Sen HN, Turriff A, Zeng Y, et al. Retinal AAV8-RS1 gene therapy for X-linked retinoschisis: Initial findings from a phase I/IIa trial by intravitreal delivery. Mol Ther 2018;26:2282-94.  Back to cited text no. 11
    
12.
Sergeev YV, Caruso RC, Meltzer MR, Smaoui N, MacDonald IM, Sieving PA. Molecular modeling of retinoschisin with functional analysis of pathogenic mutations from human X-linked retinoschisis. Hum Mol Genet 2010;19:1302-13.  Back to cited text no. 12
    


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