Torriano Simona, Erkilic Nejla, Faugère Valérie, Damodar Krishna, Hamel Christian P, Roux Anne-Francoise, Kalatzis Vasiliki
Inserm U1051, Institute for Neurosciences of Montpellier, Montpellier, France.
University of Montpellier, Montpellier, France.
Hum Mol Genet. 2017 Sep 15;26(18):3573-3584. doi: 10.1093/hmg/ddx244.
Choroideremia (CHM) is an inherited retinal dystrophy characterised by progressive degeneration of photoreceptors, retinal pigment epithelium (RPE) and underlying choroid. It is caused by loss-of-function mutations in CHM, which has an X-linked inheritance, and is thus an ideal candidate for gene replacement strategies. CHM encodes REP1, which plays a key role in the prenylation of Rab GTPases. We recently showed that an induced pluripotent stem cell (iPSc)-derived RPE model for CHM is fully functional and reproduces the underlying prenylation defect. This criterion can thus be used for testing the pathogenic nature of novel variants. Until recently, missense variants were not associated with CHM. Currently, at least nine such variants have been reported but only two have been shown to be pathogenic. We report here the characterisation of the third pathogenic missense CHM variant, p.Leu457Pro. Clinically, the associated phenotype is indistinguishable from that of loss-of-function mutations. By contrast, this missense variant results in wild type CHM expression levels and detectable levels of mutant protein. The prenylation status of patient-specific fibroblasts and iPSc-derived RPE is within the range observed for loss-of-function mutations, consistent with the clinical phenotype. Lastly, considering the current climate of CHM gene therapy, we assayed whether the presence of mutant REP1 could interfere with a gene replacement strategy by testing the prenylation status of patient-specific iPSc-derived RPE following AAV-mediated gene transfer. Our results show that correction of the functional defect is possible and highlight the predictive value of these models for therapy screening prior to inclusion in clinical trials.
无脉络膜症（CHM）是一种遗传性视网膜营养不良，其特征为光感受器、视网膜色素上皮（RPE）及下方脉络膜进行性退变。它由CHM基因功能丧失性突变引起，具有X连锁遗传，因此是基因替代策略的理想候选对象。CHM编码REP1，其在Rab GTP酶的异戊二烯化过程中起关键作用。我们最近表明，一种用于CHM的诱导多能干细胞（iPSc）来源的RPE模型功能完全正常，并再现了潜在的异戊二烯化缺陷。因此，这一标准可用于测试新变异的致病性质。直到最近，错义变异还未与CHM相关联。目前，至少已报道了9种此类变异，但只有2种被证明具有致病性。我们在此报告第三种致病性CHM错义变异p.Leu457Pro的特征。临床上，相关表型与功能丧失性突变的表型无法区分。相比之下，这种错义变异导致野生型CHM表达水平及可检测到的突变蛋白水平。患者特异性成纤维细胞和iPSc来源的RPE的异戊二烯化状态处于功能丧失性突变所观察到的范围内，与临床表型一致。最后，考虑到当前CHM基因治疗的情况，我们通过检测AAV介导的基因转移后患者特异性iPSc来源的RPE的异戊二烯化状态，来测定突变型REP1的存在是否会干扰基因替代策略。我们的结果表明功能缺陷是可以纠正的，并突出了这些模型在纳入临床试验之前进行治疗筛选的预测价值。
