Department of Biosciences, University of Helsinki, Finland.
Hum Mutat. 2011 Jan;32(1):107-15. doi: 10.1002/humu.21409.
In order to assess whether variations affecting DNA mismatch repair (MMR) genes are pathogenic and hence predisposing to Lynch syndrome (LS), a three-step assessment model has been proposed. Where LS is suspected based on family history, STEP1 is dedicated to the identification of the causative MMR gene and the variation within it. Thereafter, in STEP2 of the assessment model, the effect of the variation on the function of the protein is assessed in an in vitro MMR and in silico assays. Where LS cannot be confirmed or ruled out in STEP2, the more specific biochemical laboratory assays such as analyzing the effect of the variation on expression, localization, and interaction of the protein are required in STEP3. Here, we verified the proposed three-step assessment model and its ability to distinguish pathogenic MMR variations from variants of uncertain significance (VUS) by utilizing the clinical as well as the laboratory and in silico data of 37 MLH1, 26 MSH2, and 11 MSH6 variations. The proposed model was shown to be appropriate and proceed logically in assessing the pathogenicity of MMR variations. In fact, for MMR deficient MSH2 and MLH1 variations the first two steps seem to be sufficient as STEP3 provides no imperative information concerning the variant pathogenicity. However, the importance of STEP3 is seen in the assessment of MMR proficient variations showing discrepant in silico results as their pathogenicity cannot be confirmed or ruled out after STEP2. MSH6 variations may be applicable to the model if appropriate selection in terms of ruling out MLH1 and MSH2 variations and MLH1 promoter hypermethylation is ensured prior to the completion of STEP2. In conclusion, taking into consideration the susceptibility gene the three-step model can be utilized in an appropriate and efficient manner to determine the pathogenicity of MMR gene variations.
为了评估影响 DNA 错配修复 (MMR) 基因的变异是否具有致病性，从而导致林奇综合征 (LS)，提出了一个三步评估模型。如果根据家族史怀疑 LS，则 STEP1 专门用于确定致病 MMR 基因及其内部的变异。在此之后，在评估模型的 STEP2 中，通过体外 MMR 和计算机模拟测定来评估该变异对蛋白质功能的影响。如果在 STEP2 中无法确认或排除 LS，则需要进行更具体的生化实验室测定，例如分析变异对蛋白质表达、定位和相互作用的影响，这属于 STEP3。在这里，我们通过利用 37 个 MLH1、26 个 MSH2 和 11 个 MSH6 变异的临床、实验室和计算机数据验证了该三步评估模型及其区分致病性 MMR 变异和意义不明变异 (VUS) 的能力。该模型被证明是合适的，并且逻辑上能够评估 MMR 变异的致病性。实际上，对于 MMR 缺陷的 MSH2 和 MLH1 变异，前两步似乎已经足够，因为 STEP3 对变异的致病性没有提供强制性信息。然而，在评估表现出不一致的计算机模拟结果的 MMR 正常变异时，STEP3 的重要性就显现出来，因为在 STEP2 之后，无法确认或排除它们的致病性。如果在完成 STEP2 之前能够确保排除 MLH1 和 MSH2 变异以及 MLH1 启动子甲基化，那么 MSH6 变异可能适用于该模型。总之，考虑到易感基因，三步模型可以以适当和有效的方式用于确定 MMR 基因变异的致病性。
