Background:LMNA is a known causative gene of dilated cardiomyopathy and familial conduction disturbance. Nonsense-mediated mRNA decay, normally caused by nonsense mutations, is a safeguard process to protect cells from deleterious effects of inappropriate proteins from mutated genes. Nonsense-mediated mRNA decay induced by nonstop codon mutations is rare. We investigated the effect of an LMNA missense mutation identified in 2 families affected by cardiac laminopathy.Methods:Genomic DNA and total RNA were isolated from patients’ peripheral blood lymphocytes or cardiac tissue. LMNA-coding exons were screened by direct sequencing. Complementary DNAs were generated by a reverse transcription-polymerase chain reaction from total RNA. Quantitative polymerase chain reaction was performed to quantify the LMNA complementary DNA amount by using specific primers for lamins A and C. A minigene splicing reporter experiment was performed to assess the effect of detected variants on RNA splicing. The protein expressions of both isoforms were analyzed by Western blotting.Results:We detected a missense variant c.936 G>C (p. Q312H) at the end of exon 5 of LMNA by genomic DNA sequencing in 2 unrelated families affected by dilated cardiomyopathy and cardiac conduction disturbance. This variant was previously reported in a French family suffering from muscular dystrophy and cardiac conduction disturbance. Sequencing of complementary DNA demonstrated that the mutated allele was absent. By quantitative polymerase chain reaction assay, we confirmed a 90% reduction in LMNA complementary DNA. The minigene splicing reporter assay demonstrated a splicing error by the variant. Western blot analysis revealed that lamin A and C expressions were reduced far >50%.Conclusions:We report an LMNA missense mutation found in 2 families, which disrupted a normal splicing site, led to nonsense-mediated mRNA decay, and resulted in severe cardiac laminopathy.

中文翻译：

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LMNA 错义突变导致无义介导的 mRNA 衰减和严重扩张型心肌病。

背景：LMNA是扩张型心肌病和家族性传导障碍的已知致病基因。无义介导的 mRNA 衰变通常由无义突变引起，是保护细胞免受突变基因中不适当蛋白质的有害影响的保护过程。由不间断密码子突变引起的无义介导的 mRNA 衰变很少见。我们研究了在 2 个受心脏椎板病变影响的家族中鉴定出的LMNA错义突变的影响。方法：从患者的外周血淋巴细胞或心脏组织中分离基因组 DNA 和总 RNA。LMNA-编码外显子通过直接测序筛选。互补 DNA 是通过逆转录聚合酶链反应从总 RNA 产生的。通过使用针对核纤层蛋白 A 和 C 的特异性引物，进行定量聚合酶链反应以量化LMNA互补 DNA 量。进行小基因剪接报告实验以评估检测到的变体对 RNA 剪接的影响。通过蛋白质印迹分析两种同种型的蛋白质表达。 结果：我们在LMNA外显子 5 末端检测到错义变异 c.936 G>C (p. Q312H)通过对受扩张型心肌病和心脏传导障碍影响的 2 个无关家族进行基因组 DNA 测序。这种变异以前曾在一个患有肌肉萎缩症和心脏传导障碍的法国家庭中报道过。互补 DNA 的测序表明突变的等位基因不存在。通过定量聚合酶链反应测定，我们证实LMNA互补 DNA减少了 90% 。小基因剪接报告基因检测表明该变体存在剪接错误。Western blot分析表明，核纤层蛋白A和C的表达均减少远远> 50％。结论：我们报告的LMNA错义突变在2个家庭，扰乱了正常的剪接位点，导致无义介导的mRNA降解发现，并导致严重的心脏椎板病。