Abstract 3766: Low frequency of MLH1/MSH2 inactivation in suspected HNPCC patients from India
Authors: Bashyam Murali D. , Kotapalli Viswakalyan , Raman Ratheesh , Chaudhary Ajay K. , Gowrishankar Swarnalata , Kongara Ravikanth , A Sastry Regulagadda , G Shantiveer Uppin , D'Souza Shoba , Tester Ashavaid , Devendra Desai , Bhatt Jay , Bhaduri Anita , Shah Sudeep , Pattnaik Sujit , C Vamsy Mohana , Murthy Sudha , Thammineedi Subramanyeshwar Rao , Mukta Srinivasulu 
Published: June 2012

Abstract
Hereditary Non-Polyposis Colorectal Cancer (HNPCC) is an autosomal dominant familial syndrome resulting in colorectal cancer at a young age. It is caused mainly due to germline mutational inactivation of any one of four mismatch repair (MMR) genes viz. MSH2, MLH1, MSH6 and PMS2 resulting in the ‘mutator’ phenotype called microsatellite instability (MSI). The mutations often result in loss of protein expression which can be detected using immunohistochemistry (IHC). IHC and MSI analysis have been suggested as pre-screening methods for selection of patients for mutation analysis of MMR genes. Studies from several populations have indicated that MLH1/MSH2 inactivation may account for a majority of HNPCC cases. We earlier reported unique clinico-pathological and molecular genetic features in Indian sporadic colorectal cancer patients. We have now carried out a multi pronged analysis of suspected HNPCC patients from India. MSI screening and IHC for MLH1 and MSH2 followed by mutation analysis was employed on a panel of Indian CRC patients who were aged below 50 years at the time of diagnosis and exhibited HNPCC-specific family history. We also included patients who had multiple primary tumors or were of older age but exhibited HNPCC-specific familial involvement. As expected, a significant majority of patients (upto 80%) harbored tumors exhibiting high MSI (MSI-H) as compared to young patients without family history (only upto 20%). Surprisingly, a significantly low proportion (only about 30%) of young patients positive for family history and MSI-H exhibited loss of MLH1/MSH2 expression, perhaps due to mutations not resulting in loss of protein expression or the involvement of MSH6/PMS2 in Indian patients at a frequency higher than other populations. IHC for MSH6/PMS2 is currently underway. Mutation screening for the appropriate gene was carried out in eight patients negative for IHC using genomic DNA isolated from blood samples. Six heterozygous germline mutations (including four novel mutations) were identified; three each in MLH1 and MSH2. Studies are ongoing to determine whether the second allele in each of the six cases was inactivated through loss of heterozygosity. Interestingly, all patients in whom mutation was identified harbored tumor in the ascending colon. Three of the six mutations generate premature termination codons expected to trigger nonsense mediated decay resulting in reduced transcript levels of the respective genes. A fourth mutation (in MLH1) resulted in drastic reduction in transcript levels as determined by quantitative reverse transcription polymerase chain reaction; no such reduction was discernable in a microsatellite stable sporadic CRC sample. Analysis of effect of the remaining two mutations is currently underway. Our results therefore reveal unique features in Indian HNPCC patients; IHC for MLH1/MSH2 may not be an ideal primary screening tool to identify HNPCC patients in India.
Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 102nd Annual Meeting of the American Association for Cancer Research; 2011 Apr 2-6; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2011;71(8 Suppl):Abstract nr 3766. doi:10.1158/1538-7445.AM2011-3766