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Purpose: We report the underlying genotype and explore possible genotypic-phenotypic correlations in a large cohort of choroideremia patients. Methods: We studied prospectively a cohort of 79 patients diagnosed within a tertiary referral service for patients with retinal dystrophies. Phenotypic evaluation consisted of clinical examination, including visual acuity and residual retinal area by fundus autofluorescence (FAF). Genotype was established by sequencing. We also investigated whether particular genotypes were associated with more severe phenotypes by performing analysis of covariance (ANCOVA), with visual acuity and FAF as the dependent variables and age as the covariant. Results: A total of 74 (94%) of patients in our cohort had causative mutations by sequencing, the majority of which were anticipated to be null. Of these, 35 (47%) had insertions and deletions, 13 (18%) had mutations predicted to affect splicing, and 26 (35%) had single point mutations. In the latter case, 13 of 21 (62%) pedigrees with single point mutations were C to T transitions at C-phosphate-G (CpG) dinucleotides. These mutations were spread across 5 of only 24 CpG dinucleotides in the entire CHM cDNA. Furthermore, these 5 locations are the only sites at which C to T transitions result in a stop codon. No clear evidence was found for genotype-phenotype correlation except in the instance of a patient with a large deletion involving neighbouring sequences. Conclusions: In patients with a diagnosis of choroideremia made by a specialty service, there is a high likelihood of establishing a genetic diagnosis. The majority of causative mutations appear to be null and, therefore, may benefit from gene replacement therapy. A disproportionate number of single point mutations observed were C to T transitions, consistent with the evolutionary decay of CpG dinucleotides through methylation and subsequent deamination. Hence, the development of choroideremia in such patients may represent the unwanted consequence of human evolution; de novo mutations are predicted to arise at these sites in future generations. (ClinicalTrials.gov number, NCT01461213.).

Original publication

DOI

10.1167/iovs.16-20230

Type

Journal article

Journal

Invest Ophthalmol Vis Sci

Publication Date

01/11/2016

Volume

57

Pages

6033 - 6039

Keywords

Adaptor Proteins, Signal Transducing, Adolescent, Adult, Aged, Child, Choroideremia, DNA, DNA Mutational Analysis, Female, Fluorescein Angiography, Follow-Up Studies, Fundus Oculi, Genotype, Humans, Male, Middle Aged, Mutation, Pedigree, Phenotype, Polymerase Chain Reaction, Prospective Studies, Retina, Time Factors, Visual Acuity, Young Adult