Choroideremia is caused by loss-of-function mutations in CHM, which encodes Rab escort protein 1 (REP-1), required as a chaperone for prenylation of Rab GTPases (Rabs) by geranylgeranyl transferase II (a.k.a. Rab GGTase) [8,9]. Here, CHM is linked to choroideremia.