We describe a family with MSH6-dependent Lynch syndrome and familial pancreatic cancer and other tumours (gastric and endometrial), in the absence of colorectal neoplasia.
No CRC was found during follow-up of patients with Lynch syndrome carrying pathogenic variants in MSH6; advanced neoplasia developed over shorter follow-up time periods in patients with pathogenic variants in MLH1 or MSH2.
By confirming that the tumor was not dMMR and not MSI-H, it was concluded that his oral pharynx cancer was sporadic, rather than LS-related, and other family members carrying the mutated MSH6 are unlikely to be at above-average risk for the development of oral cancers, as a result of the LS.
Lynch syndrome (LS) is an autosomal dominant inherited disorder that is associated with an increased predisposition to certain cancers caused by loss-of-function mutations in one of four DNA mismatch repair (MMR) genes (MLH1, MSH2, MSH6, or PMS2).
We have previously shown that even a partial expression decrease in MLH1, MSH2, or MSH6 suggests that heterozygous LS mutation carriers have MMR malfunction in constitutive tissues.
Second, when we focused on Lynch syndrome (LS) with additional selected patients, 45 were identified to carry pathogenic mutations in MMR genes, with a higher frequency found in MSH2 and MSH6.
The cases demonstrated diffuse MLH1 loss associated with BRAF mutations and MLH1 promoter hypermethylation in keeping with sporadic dMMR, with presumed additional double hit mutations in MSH2+/-MSH6 rather than underlying LS.
Colon tissues were collected from patients with advanced adenomas, ≥4 nonadvanced adenomas, or CRC, and analyzed by immunohistochemistry to identify patients with loss of mismatch repair (MMR) proteins (MLH1, MSH2, MSH6, or PMS2): a marker of Lynch syndrome.
Our results suggest that MSH6 pathogenic variants are not common among Brazilian LS probands diagnosed with CRC and that MMR gene rearrangements account for a significant proportion of the germline variants in this population underscoring the need to include rearrangement analysis in the molecular testing of Brazilian individuals with suspected Lynch syndrome.
Lynch syndrome due to pathogenic variants in the DNA mismatch repair genes MLH1, MSH2, and MSH6 is predominantly associated with colorectal and endometrial cancer, although extracolonic cancers have been described within the Lynch tumor spectrum.
In humans, the importance of MMR is underscored by the discovery that a single mutation in any 1 of 4 genes within the MMR pathway (MLH1, MSH2, MSH6 and PMS2) results in Lynch syndrome (LS).
Lynch Syndrome (LS) is associated with germline mutations in one of the mismatch repair (MMR) genes, including MutL homolog 1 (MLH1), MutS homolog 2 (MSH2), MSH6, PMS1 homolog 2, mismatch repair system component (PMS2), MLH3 and MSH3.
Prediction of MLH1, MSH2, and MSH6 (PREMM<sub>1,2,6</sub>) is a web-based tool that analyzes individuals' personal/family histories of cancer to quantify their likelihood of carrying a germline mutation associated with Lynch syndrome.