Novel and recurring hMLH1 and hMSH2 mutations in Singaporean families with hereditary non-polyposis colorectal cancer

SC Lee MD^a, JY Guo MSc^a, R Lim MD^a, F Zhao BSc^a, R Soo MD^a, E Koay PhD^b, M Salto-Tellez MD^b, HL Lim MD^a, A Leong MD^c, BC Goh MD^a

^aDepartment of Haematology-Oncology, ^bDepartment of Pathology, ^cDepartment of Surgery; National University Hospital, Singapore

Aim: Hereditary non-polyposis colorectal cancer (HNPCC) is the commonest known form of hereditary colorectal cancer (CRC), and is predominantly due to germline mutations in the mismatch repair genes hMLH1 and hMSH2. Data of the prevalence and spectrum of hMLH1 and hMSH2 mutations in Asian populations is sparse. Methods: Singaporean CRC patients diagnosed below age 40, and/or with strong familial cancer clustering suggestive of HNPCC, were recruited for germline hMLH1 and hMSH2 sequencing. When available, the patient’s colon cancer tissues were tested for microsatellite instability (MSI) and immunohistochemically stained for the hMLH1 and hMSH2 proteins. Results: Forty-six unrelated high-risk patients, of Chinese, Malay, or Indian ethnicity, were recruited. Five different deleterious hMLH1 and two deleterious hMSH2 mutations have been identified in six Chinese, one Malay, and two Indian (9/46, 20%). Of these, two hMLH1 and one hMSH2 deleterious mutations were novel, and two deleterious hMLH1 mutations were recurrent in two unrelated families each. The previously reported T1151A (Val384Asp) missense mutation in Chinese occurred in 3/23 (13%) of our Chinese patients. In addition, five other novel hMSH2 exonic missense mutations of uncertain significance were identified, of which two showed linkage, and occurred in 3/23 (13%) Chinese patients, but was not found in a screen of 44 Chinese healthy blood donors. The core promoter regions of the hMLH1 and hMSH2 genes were sequenced, and results will be available. The hMLH1 and hMSH2 mutation data in our Malay and Indian families represents the first such data in these ethnic groups. 11/35 (31%) patients had MSI-high tumors, while 4/27 (15%) patients had loss of expression of the hMLH1 or hMSH2 proteins in their tumors. Family history was the strongest predictor for a positive gene test. The correlation between hMLH1/hMSH2 germline status and tumor microsatellite instability status was good though imperfect, while tumor hMLH1/hMSH2 immunohistochemical staining appears to have limited clinical utility in this pre-selected high-risk population. Conclusion: Novel and recurring hMLH1 and hMSH2 mutations occur in Singaporean HNPCC families, and family history remains the strongest predictor of a positive gene test. This information is of relevance in selecting patients for gene testing and in formulating molecular diagnostic strategies for HNPCC in Asia.

Paper presented at the International Symposium on Predictive Oncology and Intervention Strategies; Nice, France; February 7 - 10, 2004; in oral session 892 (Genetic predisposition - Part II).