Investigation of allelic imbalances on chromosome 3p in nasopharyngeal carcinoma in Tunisia: High frequency of microsatellite instability in patients with early-onset of the disease

Abstract

Tunisia is one of the world's intermediate risk areas for nasopharyngeal carcinoma (NPC). Loss of heterozygosity (LOH) on the short arm of chromosome 3 (3p) is the most frequent genetic change reported in NPC from endemic areas. In the present study, we investigate the incidence of LOH and microsatellite instability (MSI) on chromosome 3p in 49 microdissected primary NPC specimens and corresponding non-cancerous tissues from Tunisian patients using six microsatellite polymorphic markers. LOH at one or more markers was observed in 40 out of 48 informative cases (83.3%). The markers D3S1038 at 3p25.2-26.1 and D3S1076 at 3p21.1-21.2 have showed the highest frequency of LOH (51.3%), followed by D3S1067 at 3p14.3-21.1 (48.7%), D3S1568 at 3p21.3 (47.4%), D3S659 at 3p13 (15.3%), and D3S1228 at 3p14.1-14.2 (11%). Interestingly, MSI at one or more microsatellite markers was observed in 15 cases (31.2%). The highest frequency of MSI was presented by D3S1568 (18.4%), D3S1067 (17.9%), and D3S1038 (12.8%). With regard to clinicopathological features, LOH was found to be less common in young patients (under 25 years) than in adults (p=0.04), whereas MSI was found to be more frequent in patients under 45 years than in older patients (p=0.006). No significant correlation was found between LOH or MSI and the other clinicopathological features investigated including, gender, tumor size, lymph node metastasis, UICC clinical stage, and histological subtype. This study revealed different patterns of allelic imbalance on chromosome 3P in NPC between age groups in Tunisia, and suggests an alteration in the DNA mismatch repair machinery that may be, in part, responsible of the early age onset form of this disease in North African populations. More attention should be given to the mismatch repair system in the juvenile form of this disease in future studies.