Machado Patrícia M, Brandão Rita D, Cavaco Branca M, Eugénio Joana, Bento Sandra, Nave Mónica, Rodrigues Paula, Fernandes Aires, Vaz Fátima
Molecular Biology Department and Breast Cancer Risk Evaluation Clinic, Instituto Português de Oncologia de Lisboa, Francisco Gentil, Lisboa, Portugal.
J Clin Oncol. 2007 May 20;25(15):2027-34. doi: 10.1200/JCO.2006.06.9443.
BRCA2 rearrangements are rare genetic events. A large BRCA2 genomic insertion was recurrently observed in our participants, and we sought to characterize it at the molecular and phenotypic level.
We studied 210 high-risk breast/ovarian cancer families. Fifty-three probands were fully screened for BRCA1/2 mutations, and three of 53 had a large insertion in exon 3 of BRCA2. This finding was analyzed by polymerase chain reaction (PCR), reverse transcriptase PCR (RT-PCR), and sequencing. An additional 157 consecutive families were screened for this mutation by a three-step PCR method. Phenotype and haplotype analysis was also performed.
Sixteen BRCA mutations were observed in 19 of 53 patients (36% detection rate). A recurrent Alu motif insertion in position c.156_157 was observed after sequencing of an abnormal fragment obtained after the amplification of BRCA2 exon 3. RT-PCR revealed exon 3 skipping. Screening of this rearrangement identified 14 additional families (out of 157). In total, 17 (8%) of 210 high-risk families ascertained in our clinic were positive for this mutation. Segregation of a common haplotype (from D13S260 to D13S1695) confirmed a common origin, estimated to have occurred 2,400 to 2,600 years ago. The following four cancer phenotypes were observed in the 17 positive families: female breast (n = 9), male breast (n = 4), breast/ovarian (n = 2), and heterogeneous (n = 2). Male breast cancer was more frequently observed in c.156_157insAlu-positive families compared with negative families (23% v 12%, respectively), and 33% of all male breast cancer families with an identified BRCA mutation were c.156_157insAlu positive.
c.156_157insAlu is a founder mutation of Portuguese origin and is the most frequent BRCA2 rearrangement described to date.
BRCA2基因重排是罕见的遗传事件。在我们的研究对象中反复观察到一种大型BRCA2基因插入现象，我们试图从分子和表型水平对其进行特征描述。
我们研究了210个高危乳腺癌/卵巢癌家系。对53名先证者进行了BRCA1/2突变的全面筛查，其中53人中有3人在BRCA2基因的第3外显子存在大型插入。通过聚合酶链反应（PCR）、逆转录PCR（RT-PCR）和测序对这一发现进行了分析。另外157个连续家系通过三步PCR方法筛查该突变。还进行了表型和单倍型分析。
53例患者中有19例（检出率36%）观察到16种BRCA突变。对BRCA2基因第3外显子扩增后获得的异常片段进行测序，发现一个重复出现的Alu基序插入位于c.156_157位置。RT-PCR显示第3外显子跳跃。对这种重排进行筛查又发现了另外14个家系（在157个家系中）。在我们诊所确定的210个高危家系中，共有17个（8%）对该突变呈阳性。一种常见单倍型（从D13S260到D13S1695）的分离证实了其共同起源，估计发生在2400至2600年前。在这17个阳性家系中观察到以下四种癌症表型：女性乳腺癌（n = 9）、男性乳腺癌（n = 4）、乳腺癌/卵巢癌（n = 2）和异质性（n = 2）。与阴性家系相比，c.156_157insAlu阳性家系中男性乳腺癌的发生率更高（分别为23%和12%），在所有已鉴定出BRCA突变的男性乳腺癌家系中，33%为c.156_157insAlu阳性。
c.156_157insAlu是一种起源于葡萄牙的奠基者突变，是迄今为止描述的最常见的BRCA2基因重排。
