Background: The loss or low expression of DNA mismatch repair (MMR) genes can result in genomic instability and tumorigenesis. One such gene, MSH2, is mutated or rearranged in Lynch syndrome (LS), which is characterized by a high risk of tumor development, including colorectal cancer. However, many variants identified in this gene are often defined as variants of uncertain significance (VUS). In this study, we selected a variant in the 3′ untranslated region (UTR) of MSH2 (c*226A > G), identified in three affected members of a LS family and already reported in the literature as a VUS. Methods: The effect of this variant on the activity of the MMR complex was examined using a set of functional assays to evaluate MSH2 expression. Results: We found MSH2 was overexpressed compared to healthy controls, as determined by RTqPCR and Western blot analyses of total RNA and proteins, respectively, extracted from peripheral blood samples. These results were confirmed by luciferase reporter gene assays. Conclusions: We therefore speculated that, in addition to canonical inactivation via a gene mutation, MMR activity may also be modulated by changes in MMR gene expression.

Hereditary non-polyposis colorectal cancer is also known as Lynch syndrome. Lynch syndrome is associated with pathogenetic variants in one of the mismatch repair (MMR) genes. In addition to colorectal cancer, the inefficiency of the MMR system leads to a greater predisposition to cancer of the endometrium and other cancers of the abdominal sphere. Molecular diagnosis is performed to identify pathogenetic variants in MMR genes. However, for many patients with clinically suspected Lynch syndrome, it is not possible to identify a pathogenic variant in MMR genes. Molecular diagnosis is essential for referring patients to specific surveillance to prevent the development of tumors related to Lynch syndrome. This review summarizes the main aspects of Lynch syndrome and recent advances in the field and, in particular, emphasizes the factors that can lead to the loss of expression of MMR genes.

The molecular characterization of patients with Lynch syndrome (LS) involves germline testing to detect a deleterious mutation in one of the genes of the mismatch repair (MMR ) pathway. To date, however, a large proportion of patients with a clinical suspicion of LS who undergo genetic testing do not show a germline pathogenetic variant in these genes. Germline DNA from 73 patients with a clinical suspicion of LS was examined with next-generation sequencing methods, using a multigene custom panel designed and standardized by our research group, that targets a set of 15 genes. Deleterious variants were identified in 5.6% of index cases, while unclassified variants were identified in 80.3% of probands. To evaluate the pathogenicity of these uncertain variants, the American College of Medical Genetics and Genomics criteria was used, also considering wherever possible the microsatellite instability (MSI) status detected on tumor tissues as pathogenic criterion. In this manner, 8 of these uncertain significance variants were classified as likely pathogenic variants. Notably, some of these likely pathogenetic variants were also identified in the MLH3 gene that is a gene not routinely analyzed for cases with a clinical suspicion of LS. The present study highlighted the importance of verifying the pathogenicity of the numerous variants of unknown significance identified in patients for whom heredity is already clinically confirmed suggesting the importance of considering the MSI-H status on the tumor of patients carrying an uncertain variant to evaluate its pathogenicity. Moreover, the present study also suggested analyzing other MMR genes, such as MLH3 , in panels used for the molecular screening of LS.

In the last years tandem mass spectrometry (MS/MS) has become a leading technology used for neonatal screening purposes. Newborn screening by MS/MS on dried blood spot samples (DBS) has one of its items in methionine levels: the knowledge of this parameter allows the identification of infant affected by homocystinuria (cystathionine β-synthase, CBS, deficiency) but can also lead, as side effect, to identify cases of methionine adenosyltransferase (MAT) type I/III deficiency.We started an expanded newborn screening for inborn errors of metabolism in Campania region in 2007. Here we report our ten years experience on expanded newborn screening in identifying patients affected by hypermethioninemia. During this period we screened approximately 77,000 infants and identified two cases: one case of classical homocystinuria and one patient affected by defect of MAT I/III. In this paper we describe these patients and their biochemical follow-up and review the literature concerning worldwide newborn screening reports on incidence of CBS and MAT deficiency.