P-0231 Occurrence of 2152 C>T –MHS2 Mutation in Brazilian Lynch Syndrome Families

Abstract

ABSTRACT Introduction Lynch syndrome (LS) is an autosomal dominant cancer predisposition syndrome caused by germline mutations in one of the genes involved in mismatch repair (MMR): MLH1, MSH2, MSH6 and PMS2. It is the most common hereditary colorectal cancer (CRC) syndrome accounting for approximately 3-5% of all CRC diagnoses. Clinically, LS is characterized by early onset CRC (average age 45 years) as well as extra-colonic cancers, including endometrial, ovarian, gastric, small bowel, pancreas, hepatobiliary and brain tumors. The clinical diagnosis of LS is made when a family fulfills the Amsterdam criteria. Less strict criteria of Bethesda have been used to identify individuals at risk due to suggestive family history, early age at CRC onset or characteristic tumor histologies. MLH1 and MSH2 germline mutations account for the majority of known mutations in LS families (50-90%). To date, over 513 different DNA alterations have been reported principally in Western populations. One of the most interesting characteristics of the Brazilian population is its heterogeneity: apart from native populations, Brazil, especially Southern Brazil, has received immigrants from different countries, including an important contribution from Southern European (mainly Portuguese colonizers in the 16th century). In 1999, a novel mutation, consisting in a single base substitution of nucleotide 2152 C>T at exon 13 in MHS2, resulting in a glutamine amino acid change to a stop codon (Q718X), was describe in Portuguese Lynch families. The aim of this study is to assess the frequency of the c.2152 C>T mutation in MSH2 in Brazilian Lynch syndrome families. Methods Peripheral blood samples were obtained from 49 Lynch syndrome families after informed consent. DNA was extracted from leukocytes using the Ilustra blood genomicPrep Mini Spin kit (GE Healthcare) as described by the manufacturer. Exon 13 of the MSH2 gene was amplified by PCR and the resulting amplicons were separated on a ABI 3500 (Life Technologies) equipment. Results were analysed by the CLC Main WorkBench V6.1.1 software. Results The 2152 C>T - MHS2 mutation was identified in three (6.12%) of the 49 unrelated index cases, all of whom refer a Portuguese origin. All three families fulfilled Amsterdam criteria, and the mean of age at CRC diagnosis was 31 years. Conclusion In families meeting Amsterdam criteria, who very likely carry a germline MMR mutation, the initial genetic testing approach is often sequence analysis of the most commonly affected genes (MLH1 and MSH2), or targeted sequencing of the gene(s) whose product(s) is (are) not expressed in the colorectal tumor. The occurrence of the germline 2152 C>T - MHS2 mutation in Brazilian families at a considerable frequency, suggests that it may be a hotspot mutation in this region. Although the findings of this study should be confirmed in a larger series of patients, screening of Brazilian LS families for this mutation should be considered as an initial approach to diagnosis.