Non-truncating hMLH1 variants identified in Slovenian gastric cancer patients are not associated with Lynch Syndrome: a functional analysis report

Abstract

Hereditary non-polyposis colorectal cancer is the most common known genetic syndrome that predisposes to various types of cancer including gastric cancer and occures mainly due to pathogenic germline mutations in DNA mismatch repair (MMR) genes, such as MLH1, MSH2 and MSH6. Impaired MMR activity can lead to microsatellite instability (MSI) in tumor tissues. Interpreting the pathogenic significance of identified mutations in MMR genes, especially missense alterations and short in-frame deletions and insertions is challenging and functional analysis is often needed to accurately assess their pathogenicities. The purpose of this study was to evaluate functional significance of MLH1 missense mutations, previously identified in unrelated Slovenian patients with MSI-positive gastric carinomas. A novel in vivo yeast-based approach and in silico predictions were used. Variant E433Q was characterized for the first time and was shown to have no effect on MLH1 protein function. Functional analysis of amino acid rearrangement K618A, with previously reported contradictory results of its pathogenicity, suggests that the variant is a neutral polymorphism. Results of our study imply that there is either germline mutation or an epigenetic inactivation of another MMR gene, which causes MSI phenotype in the referred gastric cancer cases.

Three-step site-directed mutagenesis screen identifies pathogenic MLH1 variants associated with Lynch syndrome

“…Many laboratories have analysed its genotype-phenotype correlation, with conflicting results. Some studies claim MLH1 K618A does not affect protein expression or MMR activity and can be found in healthy individuals as frequently as in patients with LS 25–30. Other studies suggest MLH1 K618A to be a low penetrance mutation 31–38…”

Genetic Instability in Gastric Cancer

“…We also assessed two of the variants, which were described for the first time in our study (Hudler et al, 2004). We have shown that identified missense mutations were not causally associated with MSI-H phenotype in analysed gastric cancer tissues (Vogelsang & Komel, 2010).…”