Altered rep-1 expression due to substitution at position 13 of the
IVS13 splice-donor site of the choroideremia (CHM) gene

Beaufrere, L.; Rieu, Stéphanie; Hache, J.-C.; Dumur, Viviane; Claustres, Mireille; Tuffery, Sylvie

doi:10.1076/ceyr.17.7.726.5169

Cited by 2 publications

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“…In choroideremia, +3 disease-causing variants at the 5′ splice site have been reported in intron 1, 7, and 13, but the intron 7 splice donor site has a run of 8 T nucleotides immediately downstream of the deletion, which would limit the effects of the single nucleotide frameshift in these 2 patients and may make this variant unique to other noncanonical splice site variants. A variant in the intron 13 splice donor (c.1609+3A>C) was reported to cause full exon 13 skipping; however, investigations to assess for residual full-length transcripts were not undertaken. We were unable to detect REP1 expression at the low levels of mRNA detected in peripheral tissue (peripheral blood mononuclear cells).…”

Section: Discussionmentioning

confidence: 99%

Association of Messenger RNA Level With Phenotype in Patients With Choroideremia

et al. 2020

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IMPORTANCE Gene therapy is a promising treatment for choroideremia, an X-linked retinal degeneration. The required minimum level of gene expression to ameliorate degeneration rate is unknown. This can be interrogated by exploring the association between messenger RNA (mRNA) levels and phenotype in mildly affected patients with choroideremia.OBJECTIVE To analyze CHM mRNA splicing outcomes in 2 unrelated patients with the same c.940+3delA CHM splice site variant identified as mildly affected from a previous study of patients with choroideremia. DESIGN, SETTING, AND PARTICIPANTSIn this retrospective observational case series, 2 patients with c.940+3delA CHM variants treated at a single tertiary referral center were studied. In addition, a third patient with a c.940+2T>A variant that disrupts the canonical dinucleotide sequence at the same donor site served as a positive control. Data were collected from October 2013 to July 2018. MAIN OUTCOMES AND MEASURESCentral area of residual fundus autofluorescence was used as a biomarker for disease progression. CHM transcript splicing was assessed by both end point and quantitative polymerase chain reaction. Rab escort protein 1 (REP1) expression was assessed by immunoblot. RESULTSThe 2 mildly affected patients with c.940+3delA variants had large areas of residual autofluorescence for their age and longer degeneration half-lives compared with the previous cohort of patients with choroideremia. The control patient with a c.940+2T>A variant had a residual autofluorescence area within the range expected for his age. Both patients with the c.940+3delA variant expressed residual levels of full-length CHM mRNA transcripts relative to the predominant truncated transcript (mean [SEM] residual level: patient 1, 2.3% [0.3]; patient 2, 4.7% [0.2]), equivalent to approximately less than 1% of the level of full-length CHM expressed in nonaffected individuals. Full-length CHM expression was undetectable in the control patient. REP1 expression was less than the threshold for detection both in patients 1 and 2 and the control patient compared with wild-type controls. CONCLUSIONS AND RELEVANCEThese results demonstrate the first genotype-phenotype association in choroideremia. A +3 deletion in intron 7 is sufficient to cause choroideremia in a milder form. If replicated with gene therapy, these findings would suggest that relatively low expression (less than 1%) of the wild-type levels of mRNA would be sufficient to slow disease progression.

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Section: Discussionmentioning

confidence: 99%