Comprehensive mutation analysis (20 families) of the choroideremia gene reveals a missense variant that prevents the binding of REP1 with rab geranylgeranyl transferase

Choroideremia (CHM), an X-linked degen- eration of the retinal pigmented epithelium (RPE), pho- toreceptors, and choroid, ultimately leads to blindness. It is caused by loss-of-function of the CHM gene prod- uct, the Rab escort protein 1 (REP1) that is involved, together with its homologue REP2, in prenylation of Rab GTPases, key regulators of intracellular vesicular traf- fic. Here, we report the molecular characterization of 20 unrelated Italian families affected by CHM. We identi- fied 19 different mutations, nine of which are new. In most cases, we analyzed the effect of the mutations at the mRNA level. Furthermore, we demonstrated, by in vitro trancription/translation assays, that the mutated mRNAs produced truncated proteins in all cases but one. In fact, we also identified a novel REP1 missense variant (c.1520A>G; p.H507R) associated to CHM. Thus far, only two other CHM-associated missense mutations have been identified, one of which was a splicing alteration. We investigated the impact of the p.H507R amino acid change on REP1 structure and function, thus providing the first experimental demonstration that correlates a mis- sense mutation in CHM with a functional impairment of REP1. Overall, our results indicate that the REP1-Rab geranyl-geranyl transferase interaction and consequently REP1-mediated Rab prenylation is essential for RPE and photoreceptor function. Hum Mutat 32:1460-1469, 2011. C 2011 Wiley Periodicals, Inc.