July 2018
Volume 59, Issue 9
Open Access
ARVO Annual Meeting Abstract  |   July 2018
Pathological donor splice site mutations beyond the dinucleotide canonical sequence in choroideremia
Author Affiliations & Notes
  • Lewis Fry
    Nuffield Laboratory of Ophthalmology, Nuffield Department of Clinical Neurosciences & NIHR Oxford Biomedical Research Centre, University of Oxford, Oxford, United Kingdom
  • Maria In?s Patrício
    Nuffield Laboratory of Ophthalmology, Nuffield Department of Clinical Neurosciences & NIHR Oxford Biomedical Research Centre, University of Oxford, Oxford, United Kingdom
    Oxford Eye Hospital, Oxford University Hospitals NHS Foundation Trust, Oxford, United Kingdom
  • Jonathan Williams
    Oxford Medical Genetics Laboratories, The Churchill Hospital, Oxford University Hospitals NHS Foundation Trust, Oxford, United Kingdom
  • Penny Clouston
    Oxford Medical Genetics Laboratories, The Churchill Hospital, Oxford University Hospitals NHS Foundation Trust, Oxford, United Kingdom
  • Kanmin Xue
    Nuffield Laboratory of Ophthalmology, Nuffield Department of Clinical Neurosciences & NIHR Oxford Biomedical Research Centre, University of Oxford, Oxford, United Kingdom
    Oxford Eye Hospital, Oxford University Hospitals NHS Foundation Trust, Oxford, United Kingdom
  • Alun R Barnard
    Nuffield Laboratory of Ophthalmology, Nuffield Department of Clinical Neurosciences & NIHR Oxford Biomedical Research Centre, University of Oxford, Oxford, United Kingdom
    Oxford Eye Hospital, Oxford University Hospitals NHS Foundation Trust, Oxford, United Kingdom
  • Robert E MacLaren
    Nuffield Laboratory of Ophthalmology, Nuffield Department of Clinical Neurosciences & NIHR Oxford Biomedical Research Centre, University of Oxford, Oxford, United Kingdom
    Oxford Eye Hospital, Oxford University Hospitals NHS Foundation Trust, Oxford, United Kingdom
  • Footnotes
    Commercial Relationships   Lewis Fry, None; Maria Patrício, Nightstar Therapeutics Inc (P), University of Oxford (E); Jonathan Williams, None; Penny Clouston, None; Kanmin Xue, University of Oxford (E); Alun Barnard, Nightstar Therapeutics Inc (C), University of Oxford (E); Robert MacLaren, Choroideremia Research Foundation (F), Euretina (S), Nightstar Therapeutics Inc (I), Nightstar Therapeutics Inc (F), Nightstar Therapeutics Inc (E), Nightstar Therapeutics Inc (P), Nightstar Therapeutics Inc (C), Spark Therapeutics Inc (C), University of Oxford (E), University of Oxford (P)
  • Footnotes
    Support  The Rhodes Trust
Investigative Ophthalmology & Visual Science July 2018, Vol.59, 3493. doi:
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    • Get Citation

      Lewis Fry, Maria In?s Patrício, Jonathan Williams, Penny Clouston, Kanmin Xue, Alun R Barnard, Robert E MacLaren; Pathological donor splice site mutations beyond the dinucleotide canonical sequence in choroideremia. Invest. Ophthalmol. Vis. Sci. 2018;59(9):3493.

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      © ARVO (1962-2015); The Authors (2016-present)

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Abstract

Purpose : Choroideremia (CHM) is an X-linked retinal degeneration caused by mutations in the CHM gene that encodes Rab escort protein-1 (REP1). Here we describe the clinical and molecular findings of two unrelated male patients (P1 & P2), who have an identical c.940+3delA donor splice site (intron 7) CHM mutation but markedly different rates of disease progression. Since this mutation is outside the canonical splice donor site, it raises the possibility that some viable RNA transcripts might be generated in the patient with slower rate of degeneration (P1).

Methods : Clinical assessment, including visual acuity and microperimetry, was performed. Rate of disease progression was estimated based on the areas of remaining fundus autofluorescence (AF) compared to a cohort of 31 choroideremia patients with other mutations. CHM exons ± 50 bp of intronic DNA covering splice donor/acceptor sites were bidirectionally Sanger sequenced for the two index patients and a positive control patient (P3) with a mutation in the consensus splice donor site (c.940+2T>A).

Results : All three patients demonstrated typical choroideremia phenotype. P1 showed an AF area of 168.7 mm2 (aged 36 yr), compared with P2 who showed an AF area of 13.6 mm2 (aged 43 yr), and P3 who showed an AF area of 38.4 mm2 (aged 12 yr). Genotyping and phenotyping of the mother of P1 confirmed carrier status. Analysis of intronic sequence 3' to the +3delA mutation revealed a series of 7 thymine (T) nucleotides in all three patients. Hence the +3delA mutation would cause a 5' shift of the poly-T sequence by one nucleotide, thereby leaving the splice donor site otherwise identical up to the +8 position, with the exception of the A to T transversion at position +3.

Conclusions : Splice site mutations beyond the GT canonical donor sequence in intron 7 can cause choroideremia. A single transversion at position +3 appears sufficient to be pathogenic, although it can be associated with a milder form. This raises the possibility that a low level of splicing might occur despite this mutation, possibly due to alternative splice donor sequence downstream.

This is an abstract that was submitted for the 2018 ARVO Annual Meeting, held in Honolulu, Hawaii, April 29 - May 3, 2018.

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