Abi Habib Walid, Azzi Salah, Brioude Frédéric, Steunou Virginie, Thibaud Nathalie, Das Neves Cristina, Le Jule Marilyne, Chantot-Bastaraud Sandra, Keren Boris, Lyonnet Stanislas, Michot Caroline, Rossi Massimiliano, Pasquier Laurent, Gicquel Christine, Rossignol Sylvie, Le Bouc Yves, Netchine Irène
INSERM, UMR_S 938, CDR Saint-Antoine, Paris F-75012, France, Sorbonne Universités, UPMC Univ Paris 06, UMR_S 938, CDR Saint-Antoine, Paris F-75012, France, Pediatric Endocrinology, APHP, Armand Trousseau Hospital, Paris, France.
INSERM, UMR_S 938, CDR Saint-Antoine, Paris F-75012, France.
Hum Mol Genet. 2014 Nov 1;23(21):5763-73. doi: 10.1093/hmg/ddu290. Epub 2014 Jun 10.
Isolated gain of methylation (GOM) at the IGF2/H19 imprinting control region 1 (ICR1) accounts for about 10% of patients with BWS. A subset of these patients have genetic defects within ICR1, but the frequency of these defects has not yet been established in a large cohort of BWS patients with isolated ICR1 GOM. Here, we carried out a genetic analysis in a large cohort of 57 BWS patients with isolated ICR1 GOM and analyzed the methylation status of the entire domain. We found a new point mutation in two unrelated families and a 21 bp deletion in another unrelated child, both of which were maternally inherited and affected the OCT4/SOX2 binding site in the A2 repeat of ICR1. Based on data from this and previous studies, we estimate that cis genetic defects account for about 20% of BWS patients with isolated ICR1 GOM. Methylation analysis at eight loci of the IGF2/H19 domain revealed that sites surrounding OCT4/SOX2 binding site mutations were fully methylated and methylation indexes declined as a function of distance from these sites. This was not the case in BWS patients without genetic defects identified. Thus, GOM does not spread uniformly across the IGF2/H19 domain, suggesting that OCT4/SOX2 protects against methylation at local sites. These findings add new insights to the mechanism of the regulation of the ICR1 domain. Our data show that mutations and deletions within ICR1 are relatively common. Systematic identification is therefore necessary to establish appropriate genetic counseling for BWS patients with isolated ICR1 GOM.
胰岛素样生长因子2/印记控制区1（IGF2/H19 ICR1）的孤立性甲基化增加（GOM）约占贝克威思-维德曼综合征（BWS）患者的10%。这些患者中的一部分在ICR1内存在基因缺陷，但在一大群孤立性ICR1 GOM的BWS患者中，这些缺陷的发生率尚未确定。在此，我们对57例孤立性ICR1 GOM的BWS患者进行了基因分析，并分析了整个区域的甲基化状态。我们在两个无关家族中发现了一个新的点突变，在另一个无关儿童中发现了一个21 bp的缺失，两者均为母系遗传，且影响了ICR1 A2重复序列中的八聚体结合转录因子4/性别决定区Y框蛋白2（OCT4/SOX2）结合位点。基于本研究和既往研究的数据，我们估计顺式基因缺陷约占孤立性ICR1 GOM的BWS患者的20%。IGF2/H19区域八个位点的甲基化分析显示，OCT4/SOX2结合位点突变周围的位点完全甲基化，甲基化指数随与这些位点距离的增加而下降。在未发现基因缺陷的BWS患者中情况并非如此。因此，GOM并非均匀地分布在IGF2/H19区域，这表明OCT4/SOX2可防止局部位点的甲基化。这些发现为ICR1区域的调控机制增添了新的见解。我们的数据表明，ICR1内的突变和缺失相对常见。因此，有必要进行系统鉴定，以便为孤立性ICR1 GOM的BWS患者提供适当的遗传咨询。
