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A case of ocular cystinosis associated with two potentially severe CTNS mutations

Lookup NU author(s): Andrew Browning, Dr Gustavo Figueiredo, Dr Oliver Baylis, Dr Emma Montgomery, Dr Elisa Molinari, Professor Francisco Figueiredo, Professor John Sayer

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Abstract

© 2019, © 2019 Taylor & Francis Group, LLC. Background: Ocular cystinosis is a rare autosomal recessive disorder caused by one severe and one mild mutation in the CTNS gene. It is characterised by cystine deposition within the cornea and conjunctiva however, the kidneys are not affected. We report a case of ocular cystinosis caused by two potentially severe CTNS mutations and discuss the possible mechanism of renal sparing. Methods: This is an observational case report of the proband and her unaffected relatives. All subjects underwent ophthalmic examination, whilst in the proband, In vivo laser scanning confocal microscopy was used to demonstrate cystine crystals within her corneas and conjunctiva. Genetic diagnosis was confirmed by DNA sequencing of the proband and the segregation of the mutations was established in her relatives. RT-PCR of leukocyte RNA was undertaken to determine if aberrant splicing of the CTNS gene was taking place Results: The proband was found to have cystine crystals limited to the anterior corneal stroma and the conjunctiva. Sequencing of the proband’s CTNS gene found her to be a compound heterozygote for a 27bp deletion in exon8/intron 8 (c.559_561 + 24del) and a novel c.635C>T variant in exon 9 that is predicted be pathogenic and to result in the substitution of alanine with valine at amino acid position 212 (p.Ala212Val), which is within the 3 rd transmembrane spanning domain of the CTNS protein. Examination of the proband’s leukocyte RNA failed to demonstrate any aberrant CTNS gene splicing. Conclusion: We present a case of ocular cystinosis caused by two potentially severe CTNS gene mutations. The lack of renal involvement may be due to localised (ocular) aberrant CTNS RNA splicing.


Publication metadata

Author(s): Browning AC, Figueiredo GS, Baylis O, Montgomery E, Beesley C, Molinari E, Figueiredo FC, Sayer JA

Publication type: Article

Publication status: Published

Journal: Ophthalmic Genetics

Year: 2019

Volume: 40

Issue: 2

Pages: 157-160

Print publication date: 01/04/2019

Online publication date: 06/04/2019

Acceptance date: 03/03/2019

ISSN (print): 1381-6810

ISSN (electronic): 1744-5094

Publisher: Taylor and Francis Ltd

URL: https://doi.org/10.1080/13816810.2019.1592198

DOI: 10.1080/13816810.2019.1592198


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