Hereditary Cancer Program, Catalan Institute of Oncology, ICO-IDIBELL, Hospitalet de Llobregat, Spain.
Hum Mutat. 2012 Nov;33(11):1576-88. doi: 10.1002/humu.22142. Epub 2012 Jul 12.
Lynch syndrome is associated with germline mutations in DNA mismatch repair (MMR) genes. Up to 30% of DNA changes found are variants of unknown significance (VUS). Our aim was to assess the pathogenicity of eight MLH1 VUS identified in patients suspected of Lynch syndrome. All of them are novel or not previously characterized. For their classification, we followed a strategy that integrates family history, tumor pathology, and control frequency data with a variety of in silico and in vitro analyses at RNA and protein level, such as MMR assay, MLH1 and PMS2 expression, and subcellular localization. Five MLH1 VUS were classified as pathogenic: c.[248G>T(;)306G>C], c.[780C>G;788A>C], and c.791-7T>A affected mRNA processing, whereas c.218T>C (p.L73P) and c.244A>G [corrected] (p.T82A) impaired MMR activity. Two other VUS were considered likely neutral: the silent c.702G>A variant did not affect mRNA processing or stability, and c.974G>A (p.R325Q) did not influence MMR function. In contrast, variant c.25C>T (p.R9W) could not be classified, as it associated with intermediate levels of MMR activity. Comprehensive functional assessment of MLH1 variants was useful in their classification and became relevant in the diagnosis and genetic counseling of carrier families.
林奇综合征与 DNA 错配修复（MMR）基因的种系突变有关。高达 30%的发现的 DNA 变化是意义不明的变异（VUS）。我们的目的是评估 8 种在疑似林奇综合征患者中发现的 MLH1 VUS 的致病性。它们都是新的或以前未表征的。为了对它们进行分类，我们遵循了一种策略，该策略将家族史、肿瘤病理学和对照频率数据与各种基于 RNA 和蛋白质水平的体外和体外分析相结合，如 MMR 检测、MLH1 和 PMS2 表达以及亚细胞定位。5 种 MLH1 VUS 被归类为致病性：c.[248G>T(;)306G>C]、c.[780C>G;788A>C]和 c.791-7T>A 影响 mRNA 加工，而 c.218T>C（p.L73P）和 c.244A>G [更正]（p.T82A）则损害 MMR 活性。另外两种 VUS 被认为可能是中性的：无意义的 c.702G>A 变体不会影响 mRNA 加工或稳定性，而 c.974G>A（p.R325Q）不会影响 MMR 功能。相比之下，变体 c.25C>T（p.R9W）无法分类，因为它与 MMR 活性的中间水平相关。对 MLH1 变体的综合功能评估有助于对其进行分类，并在携带者家族的诊断和遗传咨询中变得相关。
