The C9orf72 repeat size correlates with onset age of disease, DNA methylation and transcriptional downregulation of the promoter.
The C9orf72 repeat size correlates with onset age of disease, DNA methylation and transcriptional downregulation of the promoter.
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DOI：
10.1038/mp.2015.159
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发表时间：
2016-08
影响因子：
11
通讯作者：
Van Broeckhoven C
中科院分区：
文献类型：
--
作者：
Gijselinck I;Van Mossevelde S;van der Zee J;Sieben A;Engelborghs S;De Bleecker J;Ivanoiu A;Deryck O;Edbauer D;Zhang M;Heeman B;Bäumer V;Van den Broeck M;Mattheijssens M;Peeters K;Rogaeva E;De Jonghe P;Cras P;Martin JJ;de Deyn PP;Cruts M;Van Broeckhoven C
位于C9 orf 72的5'调控区的G4 C2重复序列的病理性扩增是额颞叶变性（FTLD）和肌萎缩侧索硬化（ALS）的最常见遗传原因。C9 orf 72患者的发病年龄具有高度可变性，这表明存在修饰因素和/或预期。我们研究了72名患有FTLD、FTLD-ALS或ALS的比利时指数患者和61名具有C9 orf 72重复扩增的亲属。我们评估了G4 C2扩增大小对发病年龄的影响、预期的作用以及重复序列大小对甲基化和C9 orf 72启动子活性的影响。血液中G4 C2扩增大小在45至超过2100个重复单位之间变化，在72例扩增的索引患者中有5.6%存在短扩增（45-78个单位）。在两个家庭中，短扩增与疾病共分离。在血液中具有短扩张但在脑中指示马赛克的受试者显示与具有长扩张的受试者相同的病理。此外，我们提供了G4 C2扩增大小与发病年龄（P<0.05）相关的证据，最可能通过5'侧翼CpG岛的甲基化状态与血液（P<0.0001）和脑（P<0.05）中的扩增大小的相关性来解释。在几个信息丰富的C9 orf 72亲子传播中，我们确定了更早的发病年龄，增加的扩增大小和/或增加的甲基化状态（P=0.0034）的5' CpG岛，让人想起疾病的预期。同样，与正常短重复序列（2-6个单元）相比，中间重复序列（7-24个单元）显示出略高的甲基化程度（P <0.0001）和C9 orf 72启动子活性的降低（P<0.0001）。在G4 C2侧翼存在小缺失的情况下，转录活性的降低甚至更显著（P<0.0001）。在这里，我们发现C9 orf 72启动子中CpG甲基化的增加可以解释G4 C2大小的增加如何导致功能丧失，而不排除重复长度依赖性毒性功能获得。这些数据提供了对疾病机制的见解，并对诊断咨询和潜在的治疗方法具有重要意义。
Pathological expansion of a G4C2 repeat, located in the 5' regulatory region of C9orf72, is the most common genetic cause of frontotemporal lobar degeneration (FTLD) and amyotrophic lateral sclerosis (ALS). C9orf72 patients have highly variable onset ages suggesting the presence of modifying factors and/or anticipation. We studied 72 Belgian index patients with FTLD, FTLD–ALS or ALS and 61 relatives with a C9orf72 repeat expansion. We assessed the effect of G4C2 expansion size on onset age, the role of anticipation and the effect of repeat size on methylation and C9orf72 promoter activity. G4C2 expansion sizes varied in blood between 45 and over 2100 repeat units with short expansions (45–78 units) present in 5.6% of 72 index patients with an expansion. Short expansions co-segregated with disease in two families. The subject with a short expansion in blood but an indication of mosaicism in brain showed the same pathology as those with a long expansion. Further, we provided evidence for an association of G4C2 expansion size with onset age (P<0.05) most likely explained by an association of methylation state of the 5' flanking CpG island and expansion size in blood (P<0.0001) and brain (P<0.05). In several informative C9orf72 parent–child transmissions, we identified earlier onset ages, increasing expansion sizes and/or increasing methylation states (P=0.0034) of the 5' CpG island, reminiscent of disease anticipation. Also, intermediate repeats (7–24 units) showed a slightly higher methylation degree (P<0.0001) and a decrease of C9orf72 promoter activity (P<0.0001) compared with normal short repeats (2–6 units). Decrease of transcriptional activity was even more prominent in the presence of small deletions flanking G4C2 (P<0.0001). Here we showed that increased methylation of CpGs in the C9orf72 promoter may explain how an increasing G4C2 size lead to loss-of-function without excluding repeat length-dependent toxic gain-of-function. These data provide insights into disease mechanisms and have important implications for diagnostic counseling and potential therapeutic approaches.