Five-Year Structural Progression in Monozygotic Twins with MAK Exon 3- Related Retinitis Pigmentosa

Five-Year Structural Progression in Monozygotic Twins with MAK Exon 3- Related Retinitis Pigmentosa | Research Square window.SnipcartSettings = { analytics: { enabled: false } }; (function() { var accessVector = localStorage.getItem('access_vector') || ''; window.dataLayer = window.dataLayer || []; if (accessVector) { window.dataLayer.push({ user: { profile: { profileInfo: { snid: accessVector } } } }); } })(); (function(w,d,s,l,i){w[l]=w[l]||[];w[l].push({'gtm.start':new Date().getTime(),event:'gtm.js'});var f=d.getElementsByTagName(s)[0],j=d.createElement(s),dl=l!='dataLayer'?'&l='+l:'';j.async=true;j.src='https://www.googletagmanager.com/gtm.js?id='+i+dl;f.parentNode.insertBefore(j,f);})(window,document,'script','dataLayer','GTM-K279D39R'); Browse Preprints In Review Journals COVID-19 Preprints AJE Video Bytes Research Tools Research Promotion AJE Professional Editing AJE Rubriq About Preprint Platform In Review Editorial Policies Our Team Advisory Board Help Center Sign In Submit a Preprint Cite Share Download PDF Case Report Five-Year Structural Progression in Monozygotic Twins with MAK Exon 3- Related Retinitis Pigmentosa Ayham Slimi, Mariam Alqam, Alaa AlTalbishi, Yahya Alswaiti, Manar Salameh This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-9065183/v1 This work is licensed under a CC BY 4.0 License Status: Under Review Version 1 posted 7 You are reading this latest preprint version Abstract Background Retinitis Pigmentosa (RP) associated with variants in the MAK gene is a relatively uncommon form of inherited retinal degeneration, although certain variants are more prevalent in specific populations. The only reported cases are linked to a homozygous Alu insertion in exon 9, whereas the clinical course and structural progression associated with exon 3 variants have not been described. Longitudinal imaging studies in genetically identical individuals are particularly rare. We report a five-year structural retinal progression in monozygotic twins with RP associated with a genetically confirmed exon 3 deletion in the MAK gene. Case presentation Two monozygotic twin brothers aged 47 years presented with progressive nyctalopia and peripheral visual field constriction beginning at approximately 38 years of age. Neither patient had systemic disease or extraocular manifestations. At the most recent evaluation, best-corrected visual acuity was 0.3 (6/12) in both eyes of both patients. Anterior segment examination and intraocular pressure were normal. Fundus examination revealed classic signs of RP, including optic disc pallor, attenuation of retinal vessels, and peripheral bone-spicule pigmentation. Genetic testing identified a homozygous exon 3 deletion in the MAK gene, confirmed by segregation analysis. Multimodal retinal imaging, including fundus autofluorescence (FAF) and spectral-domain optical coherence tomography (SD-OCT), demonstrated progressive contraction of the ellipsoid zone (EZ) and thinning of the outer retinal layers over a five-year follow-up period. Structural progression was highly concordant between the twins, while central visual acuity remained relatively preserved with relatively mild deterioration of the visual field. Conclusions This report documents longitudinal structural retinal degeneration in monozygotic twins with RP associated with exon 3 deletion in the MAK gene. Imaging biomarkers, particularly EZ integrity on OCT, may detect disease progression earlier than visual acuity changes. These findings contribute to understanding the natural history of this rare genetic variant and highlight the value of multimodal imaging in monitoring inherited retinal diseases. retinitis pigmentosa MAK monozygotic twins optical coherence tomography ellipsoid zone Figures Figure 1 Figure 2 Background MAK -associated RP (RP62; OMIM #614181) is an autosomal recessive retinal dystrophy characterized by progressive photoreceptor degeneration and relative preservation of central visual acuity in early stages 1 , 2 . Most reported cases to date are associated with a recurrent exon 9 Alu insertion, particularly in individuals of Ashkenazi Jewish ancestry, and are typically linked to relatively mild macular involvement until later decades of life 3 . In contrast, reported variants outside exon 9 are rare, and the structural retinal changes associated with these variants remain scarce 4 , 5 . In particular, longitudinal imaging data describing macular progression in individuals with non–exon 9 variants are limited. Here, we report 5-year multimodal imaging findings in monozygotic Palestinian twins with a homozygous exon 3 deletion in the MAK gene. This report provides longitudinal structural observations of a rare coding-region variant and describes progression patterns in genetically identical individuals. Case Presentation This longitudinal case series describes monozygotic twin brothers with RP associated with a homozygous exon 3 deletion in the MAK gene. Both patients were evaluated at the St. John of Jerusalem Eye Hospital and underwent comprehensive ophthalmic examinations at baseline and follow-up visits over approximately 5 years. Clinical evaluation included best-corrected visual acuity assessment, slit-lamp biomicroscopy, intraocular pressure measurement, and dilated fundus examination. Multimodal retinal imaging was performed at baseline (2019–2020) and follow-up (2024–2025), including SD-OCT, wide-field color fundus photography, and FAF. Structural progression was assessed qualitatively by evaluating EZ integrity, outer retinal thickness, and areas of hypoautofluorescence over time. Targeted sequencing of inherited retinal disease-associated genes was performed using molecular inversion probe–based capture followed by next-generation sequencing and analysis with an in-house bioinformatics pipeline 6 . Analysis was done in-house. A homozygous exon 3 deletion in the MAK gene (NM_001242957.3) was identified in Twin A. The deletion was subsequently validated by polymerase chain reaction (PCR) and gel electrophoresis and confirmed in Twin B. Fundus examination revealed typical features of RP, including optic disc pallor, attenuated retinal vessels, and peripheral bone-spicule pigmentation (Fig. 1 A-B; Fig. 2 A-B). Baseline multimodal imaging (2019–2020) demonstrated diffuse outer retinal atrophy with relative subfoveal preservation and a residual central EZ island in both twins (Fig. 1 C; Fig. 2 C). At approximately 5-year follow-up (2024–2025), SD-OCT showed interval contraction of the EZ island and progressive parafoveal thinning in both patients while central foveal sparing persisted (Fig. 1 D; Fig. 2 D). FAF imaging demonstrated enlargement of hypoautofluorescent areas, consistent with progressive retinal pigment epithelium and photoreceptor degeneration (Fig. 1 E-F; Fig. 2 E-F). A thin nontractional epiretinal membrane (ERM) was present bilaterally in both twins and remained stable throughout follow-up. Full-field electroretinography demonstrated markedly reduced scotopic and photopic responses consistent with advanced rod–cone dystrophy. Structural progression patterns were highly concordant between the twins (Fig. 1 ; Fig. 2 ). Twin A appeared slightly more structurally advanced at follow-up, with greater contraction of the EZ island and parafoveal thinning compared with Twin B; however, both individuals demonstrated similar macular architecture and preservation of central vision. Discussion and Conclusions This longitudinal case series describes monozygotic twins with autosomal recessive RP associated with a homozygous deletion of exon 3 in the MAK gene and provides 5-year multimodal imaging follow-up. To our knowledge, this early coding-region deletion has not previously been reported in association with MAK -related RP. The exon 3 deletion identified in this family is predicted to disrupt normal MAK protein function, which plays an important role in photoreceptor ciliary regulation and protein trafficking between the inner and outer segments 7 . Disruption of these processes leads to progressive photoreceptor degeneration 7 . In this study, serial imaging demonstrated parallel contraction of the EZ island and expansion of hypoautofluorescent areas over 5 years, while best-corrected visual acuity remained stable. This structural-functional dissociation highlights the limitation of visual acuity as a sole marker of disease progression and supports the value of OCT-–based structural biomarkers. Most previously reported cases of MAK -associated RP involve the recurrent exon 9 Alu insertion, particularly in individuals of Ashkenazi Jewish ancestry, and have been associated with relatively mild macular involvement and preservation of central visual acuity into the eighth decade of life 3 . In contrast, the twins (fifth decade of life) described here demonstrated measurable macular microstructural involvement, despite preserved vision acuity with relatively mild deterioration of the visual field within 5 years follow-up period, suggesting potential phenotypic variability among non-exon 9 variants. Further follow-up in later decades is needed to determine the rate of deterioration. Although conclusions regarding genotype-specific severity cannot be drawn from two individuals, these findings contribute to the expanding phenotypic spectrum of MAK -associated disease. The use of a monozygotic twin model provides a unique opportunity to observe disease progression in a controlled genetic context. Despite minor differences in severity, both individuals exhibited highly concordant structural progression changes over time. This study has limitations. Imaging was performed using different devices across the follow-up period, which may introduce cross-platform variability in image resolution, segmentation, and measurement scaling. Nevertheless, the observed progression was characterized by clear morphologic changes - including contraction of the EZ island and expansion of hypoautofluorescent areas - that were evident across modalities and unlikely to be attributable solely to device-related differences. Quantitative EZ measurements and standardized platform imaging would further strengthen longitudinal assessment in future studies. The second limitation is the small sample size. In conclusion, this 5-year longitudinal monozygotic twin study demonstrates progressive structural retinal changes in retinitis pigmentosa associated with an exon 3 deletion in the MAK, with preserved central visual acuity despite measurable microstructural decline and relatively mild deterioration of the visual field. These observations support the use of high-resolution structural imaging as a sensitive biomarker for natural history characterization and potential therapeutic monitoring. Furthermore, they highlight the importance of comprehensive genetic testing in identifying rare variants and improving genotype–phenotype correlation in inherited retinal diseases. Abbreviations BCVA Best-corrected visual acuity ERM Epiretinal membrane EZ Ellipsoid zone FAF Fundus autofluorescence MAK Male germ cell–associated kinase OCT Optical coherence tomography OMIM Online Mendelian Inheritance in Man RP Retinitis pigmentosa RP62 Retinitis pigmentosa 62 SD-OCT Spectral-domain optical coherence tomography Declarations Ethics approval and consent to participate: The study adhered to the tenets of the Declaration of Helsinki and was approved by the institutional ethics committee of St. John Eye Hospital Group. Written informed consent for participation and publication of clinical data and imaging was obtained from both patients. Consent for publication Written informed consent was obtained from all participants for publication of this case report and any accompanying images Availability of data and materials The variant identified in this study has been submitted to the ClinVar database (Submission ID: SUB16091357) and is currently under review. The accession number will be provided upon approval. No large-scale sequencing datasets were generated. Additional data supporting the findings of this study are available from the corresponding author upon reasonable request. Competing Interests: The authors declare that they have no competing interests. Funding: This research did not receive any specific grant from funding agencies in the public, commercial, or not-for-profit sectors Authors’ Contributions: AS (First Author): Coordinated patient care, conducted imaging, collected data, coordinated referrals, follow-up and drafted the manuscript MA: Collected clinical data, contributed to analysis, manuscript writing, manuscript revision MS: Performed molecular validation experiment (PCR) of the variant, contributed to data interpretation, and revised the manuscript AA: Contributed to manuscript revision and served as research lead YA: Provided expert review, methodological oversight, major editorial revisions, and co-led the research Acknowledgements We thank all staff at St. John of Jerusalem Eye Hospital for their support in patient care and data collection. References Tucker BA, Burnight ER, Cranston CM et al. Development and biological characterization of a clinical gene transfer vector for the treatment of MAK-associated retinitis pigmentosa. Gene Therapy 2021 29:5 . 2021;29(5):259–288. 10.1038/s41434-021-00291-5 Van Huet RAC, Siemiatkowska AM, Özgül RK, et al. Retinitis pigmentosa caused by mutations in the ciliary MAK gene is relatively mild and is not associated with apparent extra-ocular features. Acta Ophthalmol. 2015;93(1):83–94. 10.1111/AOS.12500 . Stone EM, Luo X, Héon E, et al. Autosomal Recessive Retinitis Pigmentosa Caused by Mutations in the MAK Gene. Invest Ophthalmol Vis Sci. 2011;52(13):9665. 10.1167/IOVS.11-8527 . Gray JM, Orlans HO, Shanks M, Clouston P, MacLaren RE. Slowly progressive retinitis pigmentosa caused by two novel mutations in the MAK gene. Ophthalmic Genet. 2018;39(4):508–11. 10.1080/13816810.2018.1474369 . Lai YH, Capasso JE, Kaiser R, Levin AV. Intraretinal cystoid spaces in a patient with retinitis pigmentosa due to mutation in the MAK gene. Ophthalmic Genet. 2016;37(4):424–6. 10.3109/13816810.2015.1092046 . Khan MI, Christian G, Carmen A et al. Molecular inversion probe based sequence analysis of 108 genes associated with non-syndromic inherited retinal disease in 4,000 probands. Invest Ophthalmol Vis Sci. 2016;57(12). Omori Y, Chaya T, Katoh K, et al. Negative regulation of ciliary length by ciliary male germ cell-associated kinase (Mak) is required for retinal photoreceptor survival. Proc Natl Acad Sci U S A. 2010;107(52):22671–6. 10.1073/PNAS.1009437108 . Additional Declarations No competing interests reported. Cite Share Download PDF Status: Under Review Version 1 posted Reviews received at journal 08 Apr, 2026 Reviewers agreed at journal 08 Apr, 2026 Reviewers invited by journal 02 Apr, 2026 Editor assigned by journal 02 Apr, 2026 Editor invited by journal 31 Mar, 2026 Submission checks completed at journal 31 Mar, 2026 First submitted to journal 30 Mar, 2026 You are reading this latest preprint version Research Square lets you share your work early, gain feedback from the community, and start making changes to your manuscript prior to peer review in a journal. As a division of Research Square Company, we’re committed to making research communication faster, fairer, and more useful. We do this by developing innovative software and high quality services for the global research community. Our growing team is made up of researchers and industry professionals working together to solve the most critical problems facing scientific publishing. Also discoverable on Platform About Our Team In Review Editorial Policies Advisory Board Help Center Resources Author Services Accessibility API Access RSS feed Manage Cookie Preferences © Research Square 2026 | ISSN 2693-5015 (online) Privacy Policy Terms of Service Do Not Sell My Personal Information {"props":{"pageProps":{"initialData":{"identity":"rs-9065183","acceptedTermsAndConditions":true,"allowDirectSubmit":false,"archivedVersions":[],"articleType":"Case Report","associatedPublications":[],"authors":[{"id":618337741,"identity":"c67ab0ca-908d-442f-a220-4856eedce026","order_by":0,"name":"Ayham Slimi","email":"","orcid":"","institution":"St John of Jerusalem Eye Hospital Group","correspondingAuthor":false,"prefix":"","firstName":"Ayham","middleName":"","lastName":"Slimi","suffix":""},{"id":618337742,"identity":"836b9568-0d77-418c-8938-8a0e60e8fe30","order_by":1,"name":"Mariam Alqam","email":"","orcid":"","institution":"St John of Jerusalem Eye Hospital Group","correspondingAuthor":false,"prefix":"","firstName":"Mariam","middleName":"","lastName":"Alqam","suffix":""},{"id":618337743,"identity":"ae3a2b02-bf68-49f2-91ea-509f0b4ba673","order_by":2,"name":"Alaa AlTalbishi","email":"","orcid":"","institution":"St John of Jerusalem Eye Hospital Group","correspondingAuthor":false,"prefix":"","firstName":"Alaa","middleName":"","lastName":"AlTalbishi","suffix":""},{"id":618337744,"identity":"9eeedce3-6470-4b86-902e-92b5c5a28cc9","order_by":3,"name":"Yahya Alswaiti","email":"data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAZAAAAAyAQMAAABI0h/eAAAABlBMVEX///8AAABVwtN+AAAACXBIWXMAAA7EAAAOxAGVKw4bAAAA/UlEQVRIie3SsUrEMBzH8d/xl79LsWuLx/kKOQJV0YexHDj1nG+QXkE4F8X1wMFXqG+QEqiTODu7dqjg0KGDTaab0hsF8x3aLB/+IQng8/3BhArMLwcIUC0YYk+iB0KotvuQuLBEwYwhsx4l4eF7HXVQ6dN9WOnL/mh2Cqq/fxyEg5vr+AF5utUEvdywPC948Tx1EWRJFICWhSUFp6UKJEUuEjZJ3A/kxZCzntfjJMqSYzOlNATMV8MZyknrJI28mAq9ftUkqscNz0vNC3KIYWPZ/LNZ5XL2UX21XV+fiLc7PelcBjiIdu6its/AXpAj2t34rf2OTfH5fL7/1S9RPUj0+0nwlgAAAABJRU5ErkJggg==","orcid":"","institution":"St John of Jerusalem Eye Hospital Group","correspondingAuthor":true,"prefix":"","firstName":"Yahya","middleName":"","lastName":"Alswaiti","suffix":""},{"id":618337745,"identity":"057b53bc-ff97-4bfb-9846-8c110433498f","order_by":4,"name":"Manar Salameh","email":"","orcid":"","institution":"St John of Jerusalem Eye Hospital Group","correspondingAuthor":false,"prefix":"","firstName":"Manar","middleName":"","lastName":"Salameh","suffix":""}],"badges":[],"createdAt":"2026-03-08 15:23:21","currentVersionCode":1,"declarations":"","doi":"10.21203/rs.3.rs-9065183/v1","doiUrl":"https://doi.org/10.21203/rs.3.rs-9065183/v1","draftVersion":[],"editorialEvents":[],"editorialNote":"","failedWorkflow":false,"files":[{"id":106534196,"identity":"4cf277b3-3bd9-4c1b-a093-a249090acf29","added_by":"auto","created_at":"2026-04-09 15:02:12","extension":"png","order_by":1,"title":"Figure 1","display":"","copyAsset":false,"role":"figure","size":962110,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003eFive-Year Multimodal Imaging in Twin A With \u003c/strong\u003e\u003cem\u003e\u003cstrong\u003eMAK\u003c/strong\u003e\u003c/em\u003e\u003cstrong\u003e-Associated Retinitis Pigmentosa\u003c/strong\u003e. (A–B) Color fundus photographs demonstrating typical retinitis pigmentosa features. (C–D) SD-OCT scans showing contraction of the \u003cstrong\u003eEZ\u003c/strong\u003e island over 5 years. (E–F) FAF imaging demonstrating enlargement of hypoautofluorescent areas.\u003c/p\u003e","description":"","filename":"floatimage1.png","url":"https://assets-eu.researchsquare.com/files/rs-9065183/v1/242e41742fdcb583aeaa87eb.png"},{"id":106534198,"identity":"ad5a352e-b8e7-4fb1-bcfb-4b46b0f620e8","added_by":"auto","created_at":"2026-04-09 15:02:13","extension":"png","order_by":2,"title":"Figure 2","display":"","copyAsset":false,"role":"figure","size":888876,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003eFive-Year Multimodal Imaging in Twin B With \u003c/strong\u003e\u003cem\u003e\u003cstrong\u003eMAK\u003c/strong\u003e\u003c/em\u003e\u003cstrong\u003e-Associated Retinitis Pigmentosa.\u003c/strong\u003e (A–B) Color fundus photographs demonstrating typical retinitis pigmentosa features. (C–D) SD-OCT scans showing contraction of the central EZ island over 5 years. (E–F) FAF imaging demonstrating enlargement of hypoautofluorescent areas.\u003c/p\u003e","description":"","filename":"floatimage2.png","url":"https://assets-eu.researchsquare.com/files/rs-9065183/v1/dd83917ae6a77f778b6337fc.png"},{"id":107704703,"identity":"55aeec3a-1676-4f27-b57a-65376eafc9f7","added_by":"auto","created_at":"2026-04-24 08:54:56","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":1768342,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-9065183/v1/4fe5217d-21dd-4f6e-825d-62be3fb39904.pdf"}],"financialInterests":"No competing interests reported.","formattedTitle":"Five-Year Structural Progression in Monozygotic Twins with MAK Exon 3- Related Retinitis Pigmentosa","fulltext":[{"header":"Background","content":"\u003cp\u003e \u003cem\u003eMAK\u003c/em\u003e-associated RP (RP62; OMIM #614181) is an autosomal recessive retinal dystrophy characterized by progressive photoreceptor degeneration and relative preservation of central visual acuity in early stages\u003csup\u003e\u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e,\u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2\u003c/span\u003e\u003c/sup\u003e. Most reported cases to date are associated with a recurrent exon 9 Alu insertion, particularly in individuals of Ashkenazi Jewish ancestry, and are typically linked to relatively mild macular involvement until later decades of life \u003csup\u003e\u003cspan citationid=\"CR3\" class=\"CitationRef\"\u003e3\u003c/span\u003e\u003c/sup\u003e.\u003c/p\u003e \u003cp\u003eIn contrast, reported variants outside exon 9 are rare, and the structural retinal changes associated with these variants remain scarce \u003csup\u003e\u003cspan citationid=\"CR4\" class=\"CitationRef\"\u003e4\u003c/span\u003e,\u003cspan citationid=\"CR5\" class=\"CitationRef\"\u003e5\u003c/span\u003e\u003c/sup\u003e. In particular, longitudinal imaging data describing macular progression in individuals with non\u0026ndash;exon 9 variants are limited.\u003c/p\u003e \u003cp\u003eHere, we report 5-year multimodal imaging findings in monozygotic Palestinian twins with a homozygous exon 3 deletion in the \u003cem\u003eMAK\u003c/em\u003e gene. This report provides longitudinal structural observations of a rare coding-region variant and describes progression patterns in genetically identical individuals.\u003c/p\u003e"},{"header":"Case Presentation","content":"\u003cp\u003eThis longitudinal case series describes monozygotic twin brothers with RP associated with a homozygous exon 3 deletion in the \u003cem\u003eMAK\u003c/em\u003e gene. Both patients were evaluated at the St. John of Jerusalem Eye Hospital and underwent comprehensive ophthalmic examinations at baseline and follow-up visits over approximately 5 years.\u003c/p\u003e \u003cp\u003eClinical evaluation included best-corrected visual acuity assessment, slit-lamp biomicroscopy, intraocular pressure measurement, and dilated fundus examination. Multimodal retinal imaging was performed at baseline (2019–2020) and follow-up (2024–2025), including SD-OCT, wide-field color fundus photography, and FAF. Structural progression was assessed qualitatively by evaluating EZ integrity, outer retinal thickness, and areas of hypoautofluorescence over time.\u003c/p\u003e \u003cp\u003eTargeted sequencing of inherited retinal disease-associated genes was performed using molecular inversion probe–based capture followed by next-generation sequencing and analysis with an in-house bioinformatics pipeline \u003csup\u003e\u003cspan class=\"CitationRef\"\u003e6\u003c/span\u003e\u003c/sup\u003e. Analysis was done in-house. A homozygous exon 3 deletion in the \u003cem\u003eMAK\u003c/em\u003e gene (NM_001242957.3) was identified in Twin A. The deletion was subsequently validated by polymerase chain reaction (PCR) and gel electrophoresis and confirmed in Twin B.\u003c/p\u003e \u003cp\u003eFundus examination revealed typical features of RP, including optic disc pallor, attenuated retinal vessels, and peripheral bone-spicule pigmentation (Fig.\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e1\u003c/span\u003eA-B; Fig.\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e2\u003c/span\u003eA-B). Baseline multimodal imaging (2019–2020) demonstrated diffuse outer retinal atrophy with relative subfoveal preservation and a residual central EZ island in both twins (Fig.\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e1\u003c/span\u003eC; Fig.\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e2\u003c/span\u003eC). At approximately 5-year follow-up (2024–2025), SD-OCT showed interval contraction of the EZ island and progressive parafoveal thinning in both patients while central foveal sparing persisted (Fig.\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e1\u003c/span\u003eD; Fig.\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e2\u003c/span\u003eD). FAF imaging demonstrated enlargement of hypoautofluorescent areas, consistent with progressive retinal pigment epithelium and photoreceptor degeneration (Fig.\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e1\u003c/span\u003eE-F; Fig.\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e2\u003c/span\u003eE-F).\u003c/p\u003e \u003cp\u003eA thin nontractional epiretinal membrane (ERM) was present bilaterally in both twins and remained stable throughout follow-up. Full-field electroretinography demonstrated markedly reduced scotopic and photopic responses consistent with advanced rod–cone dystrophy.\u003c/p\u003e \u003cp\u003eStructural progression patterns were highly concordant between the twins (Fig.\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e1\u003c/span\u003e; Fig.\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e2\u003c/span\u003e). Twin A appeared slightly more structurally advanced at follow-up, with greater contraction of the EZ island and parafoveal thinning compared with Twin B; however, both individuals demonstrated similar macular architecture and preservation of central vision.\u003c/p\u003e "},{"header":"Discussion and Conclusions","content":"\u003cp\u003eThis longitudinal case series describes monozygotic twins with autosomal recessive RP associated with a homozygous deletion of exon 3 in the \u003cem\u003eMAK\u003c/em\u003e gene and provides 5-year multimodal imaging follow-up. To our knowledge, this early coding-region deletion has not previously been reported in association with \u003cem\u003eMAK\u003c/em\u003e-related RP.\u003c/p\u003e\u003cp\u003eThe exon 3 deletion identified in this family is predicted to disrupt normal \u003cem\u003eMAK\u003c/em\u003e protein function, which plays an important role in photoreceptor ciliary regulation and protein trafficking between the inner and outer segments \u003csup\u003e\u003cspan class=\"CitationRef\"\u003e7\u003c/span\u003e\u003c/sup\u003e. Disruption of these processes leads to progressive photoreceptor degeneration \u003csup\u003e\u003cspan class=\"CitationRef\"\u003e7\u003c/span\u003e\u003c/sup\u003e. In this study, serial imaging demonstrated parallel contraction of the EZ island and expansion of hypoautofluorescent areas over 5 years, while best-corrected visual acuity remained stable. This structural-functional dissociation highlights the limitation of visual acuity as a sole marker of disease progression and supports the value of OCT-–based structural biomarkers.\u003c/p\u003e\u003cp\u003eMost previously reported cases of \u003cem\u003eMAK\u003c/em\u003e-associated RP involve the recurrent exon 9 Alu insertion, particularly in individuals of Ashkenazi Jewish ancestry, and have been associated with relatively mild macular involvement and preservation of central visual acuity into the eighth decade of life \u003csup\u003e\u003cspan class=\"CitationRef\"\u003e3\u003c/span\u003e\u003c/sup\u003e. In contrast, the twins (fifth decade of life) described here demonstrated measurable macular microstructural involvement, despite preserved vision acuity with relatively mild deterioration of the visual field within 5 years follow-up period, suggesting potential phenotypic variability among non-exon 9 variants. Further follow-up in later decades is needed to determine the rate of deterioration. Although conclusions regarding genotype-specific severity cannot be drawn from two individuals, these findings contribute to the expanding phenotypic spectrum of \u003cem\u003eMAK\u003c/em\u003e-associated disease.\u003c/p\u003e\u003cp\u003eThe use of a monozygotic twin model provides a unique opportunity to observe disease progression in a controlled genetic context. Despite minor differences in severity, both individuals exhibited highly concordant structural progression changes over time.\u003c/p\u003e\u003cp\u003eThis study has limitations. Imaging was performed using different devices across the follow-up period, which may introduce cross-platform variability in image resolution, segmentation, and measurement scaling. Nevertheless, the observed progression was characterized by clear morphologic changes - including contraction of the EZ island and expansion of hypoautofluorescent areas - that were evident across modalities and unlikely to be attributable solely to device-related differences. Quantitative EZ measurements and standardized platform imaging would further strengthen longitudinal assessment in future studies. The second limitation is the small sample size.\u003c/p\u003e\u003cp\u003eIn conclusion, this 5-year longitudinal monozygotic twin study demonstrates progressive structural retinal changes in retinitis pigmentosa associated with an exon 3 deletion in the MAK, with preserved central visual acuity despite measurable microstructural decline and relatively mild deterioration of the visual field. These observations support the use of high-resolution structural imaging as a sensitive biomarker for natural history characterization and potential therapeutic monitoring. Furthermore, they highlight the importance of comprehensive genetic testing in identifying rare variants and improving genotype–phenotype correlation in inherited retinal diseases.\u003c/p\u003e"},{"header":"Abbreviations","content":"\u003cdiv class=\"DefinitionList\"\u003e \u003cdiv class=\"DefinitionListEntry\"\u003e \u003cdiv class=\"Term\"\u003eBCVA\u003c/div\u003e \u003cdiv class=\"Description\"\u003e \u003cp\u003eBest-corrected visual acuity\u003c/p\u003e \u003c/div\u003e \u003c/div\u003e \u003cdiv class=\"DefinitionListEntry\"\u003e \u003cdiv class=\"Term\"\u003eERM\u003c/div\u003e \u003cdiv class=\"Description\"\u003e \u003cp\u003eEpiretinal membrane\u003c/p\u003e \u003c/div\u003e \u003c/div\u003e \u003cdiv class=\"DefinitionListEntry\"\u003e \u003cdiv class=\"Term\"\u003eEZ\u003c/div\u003e \u003cdiv class=\"Description\"\u003e \u003cp\u003eEllipsoid zone\u003c/p\u003e \u003c/div\u003e \u003c/div\u003e \u003cdiv class=\"DefinitionListEntry\"\u003e \u003cdiv class=\"Term\"\u003eFAF\u003c/div\u003e \u003cdiv class=\"Description\"\u003e \u003cp\u003eFundus autofluorescence\u003c/p\u003e \u003c/div\u003e \u003c/div\u003e \u003cdiv class=\"DefinitionListEntry\"\u003e \u003cdiv class=\"Term\"\u003eMAK\u003c/div\u003e \u003cdiv class=\"Description\"\u003e \u003cp\u003eMale germ cell\u0026ndash;associated kinase\u003c/p\u003e \u003c/div\u003e \u003c/div\u003e \u003cdiv class=\"DefinitionListEntry\"\u003e \u003cdiv class=\"Term\"\u003eOCT\u003c/div\u003e \u003cdiv class=\"Description\"\u003e \u003cp\u003eOptical coherence tomography\u003c/p\u003e \u003c/div\u003e \u003c/div\u003e \u003cdiv class=\"DefinitionListEntry\"\u003e \u003cdiv class=\"Term\"\u003eOMIM\u003c/div\u003e \u003cdiv class=\"Description\"\u003e \u003cp\u003eOnline Mendelian Inheritance in Man\u003c/p\u003e \u003c/div\u003e \u003c/div\u003e \u003cdiv class=\"DefinitionListEntry\"\u003e \u003cdiv class=\"Term\"\u003eRP\u003c/div\u003e \u003cdiv class=\"Description\"\u003e \u003cp\u003eRetinitis pigmentosa\u003c/p\u003e \u003c/div\u003e \u003c/div\u003e \u003cdiv class=\"DefinitionListEntry\"\u003e \u003cdiv class=\"Term\"\u003eRP62\u003c/div\u003e \u003cdiv class=\"Description\"\u003e \u003cp\u003eRetinitis pigmentosa 62\u003c/p\u003e \u003c/div\u003e \u003c/div\u003e \u003cdiv class=\"DefinitionListEntry\"\u003e \u003cdiv class=\"Term\"\u003eSD-OCT\u003c/div\u003e \u003cdiv class=\"Description\"\u003e \u003cp\u003eSpectral-domain optical coherence tomography\u003c/p\u003e \u003c/div\u003e \u003c/div\u003e \u003c/div\u003e"},{"header":"Declarations","content":"\u003cp\u003e\u003cstrong\u003eEthics approval and consent to participate:\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe study adhered to the tenets of the Declaration of Helsinki and was approved by the institutional ethics committee of St. John Eye Hospital Group. Written informed consent for participation and publication of clinical data and imaging was obtained from both patients.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eConsent for publication\u003c/strong\u003e\u003cbr\u003e\u0026nbsp;Written informed consent was obtained from all participants for publication of this case report and any accompanying images\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eAvailability of data and materials\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe variant identified in this study has been submitted to the ClinVar database (Submission ID: SUB16091357) and is currently under review. The accession number will be provided upon approval. No large-scale sequencing datasets were generated. Additional data supporting the findings of this study are available from the corresponding author upon reasonable request.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eCompeting Interests:\u003c/strong\u003e The authors declare that they have no competing interests.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eFunding:\u003c/strong\u003e This research did not receive any specific grant from funding agencies in the public, commercial, or not-for-profit sectors\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eAuthors’ Contributions:\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eAS (First Author):\u003c/strong\u003e Coordinated patient care, conducted imaging, collected data, coordinated referrals, follow-up and drafted the manuscript\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eMA:\u003c/strong\u003e Collected clinical data, contributed to analysis, manuscript writing, manuscript revision\u003cbr\u003e\u003cstrong\u003eMS:\u0026nbsp;\u003c/strong\u003ePerformed molecular validation experiment (PCR) of the variant, contributed to data interpretation, and revised the manuscript\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eAA:\u003c/strong\u003e Contributed to manuscript revision and served as research lead\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eYA:\u003c/strong\u003e Provided expert review, methodological oversight, major editorial revisions, and co-led the research\u003c/p\u003e\n\u003cp\u003e\u0026nbsp;\u003cstrong\u003eAcknowledgements\u003c/strong\u003e\u003cbr\u003e\u0026nbsp;We thank all staff at St. John of Jerusalem Eye Hospital for their support in patient care and data collection.\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\u003cli\u003e\u003cspan\u003eTucker BA, Burnight ER, Cranston CM et al. Development and biological characterization of a clinical gene transfer vector for the treatment of MAK-associated retinitis pigmentosa. \u003cem\u003eGene Therapy 2021 29:5\u003c/em\u003e. 2021;29(5):259\u0026ndash;288. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003e10.1038/s41434-021-00291-5\u003c/span\u003e\u003cspan address=\"10.1038/s41434-021-00291-5\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eVan Huet RAC, Siemiatkowska AM, \u0026Ouml;zg\u0026uuml;l RK, et al. Retinitis pigmentosa caused by mutations in the ciliary MAK gene is relatively mild and is not associated with apparent extra-ocular features. Acta Ophthalmol. 2015;93(1):83\u0026ndash;94. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003e10.1111/AOS.12500\u003c/span\u003e\u003cspan address=\"10.1111/AOS.12500\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eStone EM, Luo X, H\u0026eacute;on E, et al. Autosomal Recessive Retinitis Pigmentosa Caused by Mutations in the MAK Gene. Invest Ophthalmol Vis Sci. 2011;52(13):9665. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003e10.1167/IOVS.11-8527\u003c/span\u003e\u003cspan address=\"10.1167/IOVS.11-8527\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eGray JM, Orlans HO, Shanks M, Clouston P, MacLaren RE. Slowly progressive retinitis pigmentosa caused by two novel mutations in the \u003cem\u003eMAK\u003c/em\u003e gene. Ophthalmic Genet. 2018;39(4):508\u0026ndash;11. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003e10.1080/13816810.2018.1474369\u003c/span\u003e\u003cspan address=\"10.1080/13816810.2018.1474369\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eLai YH, Capasso JE, Kaiser R, Levin AV. Intraretinal cystoid spaces in a patient with retinitis pigmentosa due to mutation in the \u003cem\u003eMAK\u003c/em\u003e gene. Ophthalmic Genet. 2016;37(4):424\u0026ndash;6. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003e10.3109/13816810.2015.1092046\u003c/span\u003e\u003cspan address=\"10.3109/13816810.2015.1092046\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eKhan MI, Christian G, Carmen A et al. Molecular inversion probe based sequence analysis of 108 genes associated with non-syndromic inherited retinal disease in 4,000 probands. Invest Ophthalmol Vis Sci. 2016;57(12).\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eOmori Y, Chaya T, Katoh K, et al. Negative regulation of ciliary length by ciliary male germ cell-associated kinase (Mak) is required for retinal photoreceptor survival. Proc Natl Acad Sci U S A. 2010;107(52):22671\u0026ndash;6. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003e10.1073/PNAS.1009437108\u003c/span\u003e\u003cspan address=\"10.1073/PNAS.1009437108\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e.\u003c/span\u003e\u003c/li\u003e\u003c/ol\u003e"}],"fulltextSource":"","fullText":"","funders":[],"hasAdminPriorityOnWorkflow":false,"hasManuscriptDocX":true,"hasOptedInToPreprint":true,"hasPassedJournalQc":"","hasAnyPriority":false,"hideJournal":false,"highlight":"","institution":"","isAcceptedByJournal":false,"isAuthorSuppliedPdf":false,"isDeskRejected":"","isHiddenFromSearch":false,"isInQc":false,"isInWorkflow":false,"isPdf":false,"isPdfUpToDate":true,"isWithdrawnOrRetracted":false,"journal":{"display":true,"email":"[email protected]","identity":"bmc-ophthalmology","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"boph","sideBox":"Learn more about [BMC Ophthalmology](http://bmcophthalmol.biomedcentral.com/)","snPcode":"","submissionUrl":"https://www.editorialmanager.com/boph","title":"BMC Ophthalmology","twitterHandle":"BMC_series","acdcEnabled":true,"dfaEnabled":false,"editorialSystem":"em","reportingPortfolio":"BMC Series","inReviewEnabled":true,"inReviewRevisionsEnabled":true},"keywords":"retinitis pigmentosa, MAK, monozygotic twins, optical coherence tomography, ellipsoid zone","lastPublishedDoi":"10.21203/rs.3.rs-9065183/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-9065183/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003cp\u003eBackground\u003cbr\u003e\nRetinitis Pigmentosa (RP) associated with variants in the MAK gene is a relatively uncommon form of inherited retinal degeneration, although certain variants are more prevalent in specific populations. The only reported cases are linked to a homozygous Alu insertion in exon 9, whereas the clinical course and structural progression associated with exon 3 variants have not been described. Longitudinal imaging studies in genetically identical individuals are particularly rare. We report a five-year structural retinal progression in monozygotic twins with RP associated with a genetically confirmed exon 3 deletion in the MAK gene.\u003c/p\u003e\n\u003cp\u003eCase presentation\u003cbr\u003e\nTwo monozygotic twin brothers aged 47 years presented with progressive nyctalopia and peripheral visual field constriction beginning at approximately 38 years of age. Neither patient had systemic disease or extraocular manifestations. At the most recent evaluation, best-corrected visual acuity was 0.3 (6/12) in both eyes of both patients. Anterior segment examination and intraocular pressure were normal. Fundus examination revealed classic signs of RP, including optic disc pallor, attenuation of retinal vessels, and peripheral bone-spicule pigmentation. Genetic testing identified a homozygous exon 3 deletion in the MAK gene, confirmed by segregation analysis. Multimodal retinal imaging, including fundus autofluorescence (FAF) and spectral-domain optical coherence tomography (SD-OCT), demonstrated progressive contraction of the ellipsoid zone (EZ) and thinning of the outer retinal layers over a five-year follow-up period. Structural progression was highly concordant between the twins, while central visual acuity remained relatively preserved with relatively mild deterioration of the visual field.\u003c/p\u003e\n\u003cp\u003eConclusions\u003cbr\u003e\nThis report documents longitudinal structural retinal degeneration in monozygotic twins with RP associated with exon 3 deletion in the MAK gene. Imaging biomarkers, particularly EZ integrity on OCT, may detect disease progression earlier than visual acuity changes. These findings contribute to understanding the natural history of this rare genetic variant and highlight the value of multimodal imaging in monitoring inherited retinal diseases.\u003c/p\u003e","manuscriptTitle":"Five-Year Structural Progression in Monozygotic Twins with MAK Exon 3- Related Retinitis Pigmentosa","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2026-04-09 15:02:07","doi":"10.21203/rs.3.rs-9065183/v1","editorialEvents":[{"type":"communityComments","content":0},{"type":"editorInvitedReview","content":"","date":"2026-04-08T14:44:20+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"257933275356121272526755480650071522791","date":"2026-04-08T10:24:14+00:00","index":"hide","fulltext":""},{"type":"reviewersInvited","content":"","date":"2026-04-02T13:20:56+00:00","index":"","fulltext":""},{"type":"editorAssigned","content":"","date":"2026-04-02T13:19:16+00:00","index":"","fulltext":""},{"type":"editorInvited","content":"","date":"2026-03-31T11:27:24+00:00","index":"","fulltext":""},{"type":"checksComplete","content":"","date":"2026-03-31T05:41:46+00:00","index":"","fulltext":""},{"type":"submitted","content":"BMC Ophthalmology","date":"2026-03-30T20:50:32+00:00","index":"","fulltext":""}],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"bmc-ophthalmology","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"boph","sideBox":"Learn more about [BMC Ophthalmology](http://bmcophthalmol.biomedcentral.com/)","snPcode":"","submissionUrl":"https://www.editorialmanager.com/boph","title":"BMC Ophthalmology","twitterHandle":"BMC_series","acdcEnabled":true,"dfaEnabled":false,"editorialSystem":"em","reportingPortfolio":"BMC Series","inReviewEnabled":true,"inReviewRevisionsEnabled":true}}],"origin":"","ownerIdentity":"a65630fe-8975-4edc-98d5-4c3dbe8d82fe","owner":[],"postedDate":"April 9th, 2026","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"under-review","subjectAreas":[],"tags":[],"updatedAt":"2026-04-09T15:02:08+00:00","versionOfRecord":[],"versionCreatedAt":"2026-04-09 15:02:07","video":"","vorDoi":"","vorDoiUrl":"","workflowStages":[]},"version":"v1","identity":"rs-9065183","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-9065183","identity":"rs-9065183","version":["v1"]},"buildId":"XKTyCvWXoU3ODBz1xrDgd","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}