Aissi-Ben Moussa Sana, Moussa Amel, Lovecchio Tonio, Kourda Nadia, Najjar Taoufik, Ben Jilani Sarra, El Gaaied Amel, Porchet Nicole, Manai Mohamed, Buisine Marie-Pierre
Laboratoire de Biochimie et Biologie Moléculaire, Faculté des Sciences de Tunis, Tunis, Tunisia.
Fam Cancer. 2009;8(2):119-26. doi: 10.1007/s10689-008-9215-7. Epub 2008 Sep 16.
High rates of early colorectal cancers are observed in Tunisia suggesting high genetic susceptibility. Nevertheless, up to now no molecular studies have been performed. Hereditary nonpolyposis colorectal cancer (HNPCC) is the most frequent cause of inherited colorectal cancer. It is caused by constitutional mutations in the DNA mismatch repair (MMR) genes. Here, we investigated a Tunisian family highly suspected of hereditary nonpolyposis colorectal cancer (HNPCC). Six patients were diagnosed with a colorectal or an endometrial cancer at an early age, including one young female who developed a colorectal cancer at 22 years and we tested for germline mutations in MMR genes. MMR genes were tested for rearrangements by MLPA (MLH1, MSH2) and the presence of point mutations by sequencing (MLH1, MSH2, MSH6). Moreover, tumors were analyzed for microsatellite instability and expression of MMR proteins, as well as for somatic rearrangements in MLH1 and MSH2 by MLPA. MMR gene analysis by MLPA revealed the presence of a large deletion in MLH1 removing exon 6. Sequence analysis of the breakpoint region showed that this rearrangement resulted from a homologous unequal recombination mediated by a repetitive Alu sequence. Moreover, tumors harbored biallelic deletion of MLH1 exon 6 and loss of heterozygosity at MLH1 intragenic markers, suggesting duplication of the rearranged allele in the tumor. This germline MLH1 rearrangement was associated to a severe phenotype in this family. This is the first report of a molecular analysis in a Tunisian family with HNPCC.
突尼斯早期结直肠癌发病率较高，提示遗传易感性较高。然而，截至目前尚未进行分子研究。遗传性非息肉病性结直肠癌（HNPCC）是遗传性结直肠癌最常见的病因。它由DNA错配修复（MMR）基因的先天性突变引起。在此，我们对一个高度怀疑患有遗传性非息肉病性结直肠癌（HNPCC）的突尼斯家族进行了调查。6名患者在早年被诊断患有结直肠癌或子宫内膜癌，其中一名年轻女性在22岁时患了结直肠癌，我们对MMR基因的种系突变进行了检测。通过MLPA检测MMR基因的重排（MLH1、MSH2），通过测序检测点突变的存在（MLH1、MSH2、MSH6）。此外，对肿瘤进行微卫星不稳定性、MMR蛋白表达分析，以及通过MLPA检测MLH1和MSH2中的体细胞重排。MLPA对MMR基因的分析显示MLH1存在一个大的缺失，缺失外显子6。断点区域的序列分析表明，这种重排是由一个重复的Alu序列介导的同源不等位重组导致的。此外，肿瘤中存在MLH1外显子6的双等位基因缺失以及MLH1基因内标记的杂合性缺失，提示肿瘤中重排等位基因的重复。这种种系MLH1重排在该家族中与严重表型相关。这是突尼斯一个HNPCC家族分子分析的首次报告。
