Mutational analysis of patients with the diagnosis of choroideremia

All reported mutations in the choroideremia (CHM) gene result in the truncation or complete absence of Rab escort protein 1 (REP1). Molecular analysis was carried out on 57 families diagnosed with CHM. Confirmation of the clinical diagnosis is important as end-stage CHM may be clinically similar to the end stages of other retinal degenerative diseases such as RP. The primary means of confirming the diagnosis of CHM is to sequence all 15 exons. An alternative method involves detection of the REP1 protein, as described in MacDonald et al. [1998]. A monoclonal antibody to REP1 does not detect truncated REP1 by immunoblot analysis, presumably due to instability and subsequent degradation of the truncated protein. This analysis provides relatively fast confirmation of the diagnosis, however, protein samples are not always available and are susceptible to degradation, affecting the accurate interpretation of results. CHM gene mutations were found in 54 of 57 families studied. The majority of mutations (>42%) were transitions and transversions. Complete deletions of the CHM gene and deletion/insertion mutations each accounted for almost 4% of the total, while over 9% had large intragenic and other partial deletions. Almost 28% of the mutations were deletions of fewer than 5 base pairs (bp) and almost 13% were splice site mutations. Despite the fact that mutations are found throughout the gene with no common mutation for the disorder, identical mutations have been characterized in unrelated individuals. The majority of these mutations are C to T transitions, changing an arginine residue (CGA) to a stop codon (TGA). Four of the five CGA codons in the CHM gene are sites of recurring mutations.