CHM and blindness (disorder): Another form of inherited retinal degeneration where significant progress has been achieved recently is choroideremia, which has an estimated prevalence of 1 in 50 000.40 It is an X-linked disorder caused by null mutations in the CHM gene and the lack of the encoded Rab escort protein-1 (REP1) accounts for the neurodegenerative process.41, 42 Loss of night vision begins in the first decade of life and there is gradual loss of peripheral vision leading to legal blindness by the fifth decade of life.