AIMS We aimed to unravel the genetic, molecular and cellular pathomechanisms of DSC2 truncation variants leading to arrhythmogenic cardiomyopathy (ACM). METHODS AND RESULTS We report a homozygous 4-bp DSC2 deletion variant c.1913_1916delAGAA, p.Q638LfsX647hom causing a frameshift carried by an ACM patient. Whole exome sequencing and comparative genomic hybridization analysis support a loss of heterozygosity in a large segment of chromosome 18 indicating segmental interstitial uniparental isodisomy (UPD). Ultrastructural analysis of the explanted myocardium from a mutation carrier using transmission electron microscopy revealed a partially widening of the intercalated disc. Using qRT-PCR we demonstrated that DSC2 mRNA expression was substantially decreased in the explanted myocardial tissue of the homozygous carrier compared to controls. Western blot analysis revealed absence of both full-length desmocollin-2 isoforms. Only a weak expression of the truncated form of desmocollin-2 was detectable. Immunohistochemistry showed that the truncated form of desmocollin-2 did not localize at the intercalated discs. In vitro, transfection experiments using induced pluripotent stem cell derived cardiomyocytes and HT-1080 cells demonstrated an obvious absence of the mutant truncated desmocollin-2 at the plasma membrane. Immunoprecipitation in combination with fluorescence measurements and Western blot analyses revealed an abnormal secretion of the truncated desmocollin-2. CONCLUSION In summary, we unraveled segmental UPD as the likely genetic reason for a small homozygous DSC2 deletion. We conclude that a combination of nonsense mediated mRNA decay and extracellular secretion is involved in DSC2 related ACM.

中文翻译：

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与单律性等轴切引起的与心律失常性心肌病相关的纯合DSC2缺失。

目的我们旨在揭示导致心律失常性心肌病（ACM）的DSC2截短变异体的遗传，分子和细胞病理机制。方法和结果我们报道了纯合的4-bp DSC2缺失变体c.1913_1916delAGAA，p.Q638LfsX647hom引起ACM患者携带的移码。完整的外显子组测序和比较基因组杂交分析支持18号染色体很大一部分杂合性的丧失，表明节段性单亲等位基因切割（UPD）。使用透射电子显微镜对突变载体植入的心肌进行超微结构分析，发现插入的椎间盘部分变宽。使用qRT-PCR，我们证明与对照相比，纯合载体的植入的心肌组织中DSC2 mRNA表达显着降低。蛋白质印迹分析表明，两种全长desmocollin-2亚型均不存在。仅检测到desmocollin-2的截短形式的弱表达。免疫组织化学显示，desmocollin-2的截短形式未定位在插入的椎间盘上。在体外，使用诱导的多能干细胞衍生的心肌细胞和HT-1080细胞进行的转染实验表明，在质膜上明显没有突变的截短的desmocollin-2。免疫沉淀与荧光测量和蛋白质印迹分析相结合，发现截短的desmocollin-2分泌异常。结论总的来说，我们揭示了节段性UPD为小纯合DSC2缺失的可能遗传原因。