Abstract
Purpose::
Choroideremia (CHM) is a juvenile onset, X-linked disease caused by mutations in the Rab Escort Protein 1 gene (REP1). Mutations in REP1 underlying CHM share a common disease mechanism of nonsense mediated decay due to truncation of the messenger by nonsense, splice site, and frame-shifting mutations. Disease causing missense mutations have not been identified so far. Here we report an overview on novel mutations identified in a European wide collected sample of CHM patients.
Methods::
Ninety-one index cases (73 male with a diagnosis of CHM, 14 carriers, and 4 males for differential diagnosis) have been accumulated and screened by SSCP for mutations in REP1 after exon specific PCR. Amplimer showing aberrant banding in SSCP were subjected to direct sequencing. Mutations identified were verified by either direct sequencing of the reverse strand or by restriction enzyme digest.
Results::
In 30% of our patients, mutations were identified by exon specific screening methods. So far six nonsense mutations, eleven intragenic deletions, five intragenic insertions, and one splice site mutation, as well as three microdeletions covering the whole gene including flanking sequences of REP1 have been identified. 81% of the identified mutations were novel and the remaining mutations have already been reported in other studies. We identified a novel single missense mutation in exon 15 and excluded its pathogenicity by segregation analysis.
Conclusions::
We found a major fraction of novel mutations among the sequence changes we identified. This hampers the application of mass screening techniques in CHM patients because of private mutations. Applying exon specific screening methods, we identified mutations in about half of the fraction of patients reported from other studies. This may be due to as yet not screened promoter mutations or phenocopies in patients referred for differential diagnosis.
Keywords: retinal degenerations: hereditary • gene screening • genetics