Background

Choroideremia is an X-linked retinal disease characterized by progressive atrophy of the choroid and retinal pigment epithelium caused by mutations in the CHM gene. SVA (SINE-R/VNTR/Alu) elements are a type of non-autonomous retrotransposon that occasionally self-replicate, reinsert randomly into a gene, and cause disease. Intragenic SVA insertions have been reported as the mechanism underlying a number of diseases including a syndromic form of retinal dystrophy, but have never been found in CHM.

Materials and Methods

Here we identified and characterized a novel hemizygous SVA insertion, c.97_98inSVA (p.Arg33insSVA), in exon 2 of CHM in a male choroideremia patient. The SVA insertion’s impact was evaluated by establishing a patient-derived lymphoblastoid cell line as a source of RNA for mRNA analysis of the CHM transcript, and protein for immunoblot analysis of Rab Escort Protein 1 (REP-1).

Results

Immunoblot analysis revealed the absence of REP-1 protein, while a smaller than expected PCR product was amplified from cDNA. Sequencing of this PCR product showed skipping of exon 2, denoted r.50_116del. Ophthalmic examination including psychophysical tests, visual electrophysiology, and fundus imaging showed the patient’s phenotype was consistent with severe early manifestations of choroideremia.

Conclusions

This case is the first report of a SVA insertion in the CHM gene causing choroideremia.

中文翻译：

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CHM 基因中的新型 SVA 反转录转座子插入导致 REP-1 丢失，从而导致无脉络膜血症。

背景

脉络膜血症是一种 X 连锁视网膜疾病，其特征是由CHM基因突变引起的脉络膜和视网膜色素上皮进行性萎缩。SVA (SINE-R/VNTR/ Alu ) 元件是一种非自主性逆转录转座子，偶尔会自我复制、随机重新插入基因并引起疾病。据报道，基因内 SVA 插入是许多疾病的潜在机制，包括视网膜营养不良的综合征形式，但从未在CHM 中发现。

材料和方法

在这里，我们在男性无脉络膜血症患者的CHM外显子 2 中鉴定并表征了一种新的半合子 SVA 插入，c.97_98inSVA (p.Arg33insSVA) 。SVA 插入的影响是通过建立患者来源的淋巴母细胞系作为 RNA 来源来评估的，用于CHM转录物的mRNA 分析，以及用于 Rab Escort 蛋白 1 (REP-1) 免疫印迹分析的蛋白质。

结果

免疫印迹分析显示不存在 REP-1 蛋白，而从 cDNA 中扩增出小于预期的 PCR 产物。该 PCR 产物的测序显示外显子 2 的跳跃，表示为 r.50_116del。眼科检查包括心理物理测试、视觉电生理学和眼底成像显示患者的表型与脉络膜血症的严重早期表现一致。

结论

该病例是CHM基因中SVA 插入导致无脉络膜血症的首次报道。