Comprehensive analysis of the MLH1 promoter region in 480 patients with colorectal cancer and 1150 controls reveals new variants including one with a heritable constitutional MLH1 epimutation
Comprehensive analysis of the MLH1 promoter region in 480 patients with colorectal cancer and 1150 controls reveals new variants including one with a heritable constitutional MLH1 epimutation
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DOI：
10.1136/jmedgenet-2017-104744
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发表时间：
2018-04-01
影响因子：
4
通讯作者：
Holinski-Feder, Elke
中科院分区：
文献类型：
--
作者：
Morak, Monika;Ibisler, Ayseguel;Holinski-Feder, Elke
背景：导致Lynch综合征（LS）的MLH 1、MSH 2、MSH 6和PMS 2的生殖系缺陷主要基于序列改变，而MLH 1的体质表型突变（CEM）非常罕见。这种异常的MLH 1启动子甲基化是不遗传的，当从头出现，而一个稳定的遗传和变异诱导的CEM被描述为一个单一的等位基因。方法我们分析了5个不同的结直肠癌（CRC）患者组（n=480）中的MLH 1启动子序列，这些患者包括i）CEM（n=16），ii）CRC中MLH 1表达未解决的缺失（n=37），iii）CpG岛甲基化子表型CRC（n=102），iv）LS患者（n=83）和v）MLH 1-熟练CRC（n=242）作为对照。1150例非LS肿瘤患者也作为对照，以正确判断结果。一种新的复杂MLH 1变体c.- 63_-58 delins 18存在于患有CEM的CRC患者及其姐妹中，两者均显示出完全的等位基因特异性启动子甲基化和转录沉默。在17个个体中检测到的其他9个启动子变异与甲基化无关。对于其中四个，一个正常的，双等位基因MLH 1的表达被发现在患者的cDNA.Conclusion我们报告的第二个启动子变体稳定诱导遗传性CEM。关于启动子变体的分类，我们讨论了两种变体的文献中相互矛盾的结果，描述了五种变体的现有规则之间的分类差异，建议将五种启动子变体（可能）分类为良性，并将四种变体视为功能不清楚。
Background Germline defects in MLH1, MSH2, MSH6 and PMS2 predisposing for Lynch syndrome (LS) are mainly based on sequence changes, whereas a constitutional epimutation of MLH1(CEM) is exceptionally rare. This abnormal MLH1 promoter methylation is not hereditary when arising de novo, whereas a stably heritable and variant-induced CEM was described for one single allele. We searched for MLH1 promoter variants causing a germline or somatic methylation induction or transcriptional repression.Methods We analysed the MLH1 promoter sequence in five different patient groups with colorectal cancer (CRC) (n=480) composed of patients with i) CEM (n=16), ii) unsolved loss of MLH1 expression in CRC (n=37), iii) CpG-island methylator-phenotype CRC (n=102), iv) patients with LS (n=83) and v) MLH1-proficient CRC (n=242) as controls. 1150 patients with non-LS tumours also served as controls to correctly judge the results.Results We detected 10 rare MLH1 promoter variants. One novel, complex MLH1 variant c.-63_-58delins18 is present in a patient with CRC with CEM and his sister, both showing a complete allele-specific promoter methylation and transcriptional silencing. The other nine promoter variants detected in 17 individuals were not associated with methylation. For four of these, a normal, biallelic MLH1 expression was found in the patients' cDNA.Conclusion We report the second promoter variant stably inducing a hereditary CEM. Concerning the classification of promoter variants, we discuss contradictory results from the literature for two variants, describe classification discrepancies between existing rules for five variants, suggest the (re-)classification of five promoter variants to (likely) benign and regard four variants as functionally unclear.