Weitzel Jeffrey N, Lagos Veronica I, Herzog Josef S, Judkins Thaddeus, Hendrickson Brant, Ho Jason S, Ricker Charité N, Lowstuter Katrina J, Blazer Kathleen R, Tomlinson Gail, Scholl Tom
Department of Clinical Cancer Genetics, City of Hope, 1500 East Duarte Road, Duarte, CA 91010, USA.
Cancer Epidemiol Biomarkers Prev. 2007 Aug;16(8):1615-20. doi: 10.1158/1055-9965.EPI-07-0198. Epub 2007 Jul 23.
Large rearrangements account for 8% to 15% of deleterious BRCA mutations, although none have been characterized previously in individuals of Mexican ancestry.
DNA from 106 Hispanic patients without an identifiable BRCA mutation by exonic sequence analysis was subjected to multiplexed quantitative differential PCR. One case of Native American and African American ancestry was identified via multiplex ligation-dependent probe amplification. Long-range PCR was used to confirm deletion events and to clone and sequence genomic breakpoints. Splicing patterns were derived by sequencing cDNA from reverse transcription-PCR of lymphoblastoid cell line RNA. Haplotype analysis was conducted for recurrent mutations.
The same deletion of BRCA1 exons 9 through 12 was identified in five unrelated families. Long-range PCR and sequencing indicated a deletion event of 14.7 kb. A 3-primer PCR assay was designed based on the deletion breakpoints, identified within an AluSp element in intron 8 and an AluSx element in intron 12. Haplotype analysis confirmed common ancestry. Analysis of cDNA showed direct splicing of exons 8 to 13, resulting in a frameshift mutation and predicted truncation of the BRCA1 protein.
We identified and characterized a novel large BRCA1 deletion in five unrelated families-four of Mexican ancestry and one of African and Native American ancestry, suggesting the possibility of founder effect of Amerindian or Mestizo origin. This BRCA1 rearrangement was detected in 3.8% (4 of 106) of BRCA sequence-negative Hispanic families. An assay for this mutation should be considered for sequence-negative high-risk Hispanic patients.
大片段重排在有害的BRCA突变中占8%至15%，尽管此前尚未在墨西哥裔个体中进行过特征描述。
对106名通过外显子序列分析未发现可识别BRCA突变的西班牙裔患者的DNA进行多重定量差异PCR。通过多重连接依赖探针扩增鉴定出1例美洲原住民和非裔美国人血统的病例。使用长距离PCR确认缺失事件，并克隆和测序基因组断点。通过对淋巴母细胞系RNA进行逆转录PCR后的cDNA测序得出剪接模式。对复发性突变进行单倍型分析。
在5个不相关的家族中鉴定出相同的BRCA1外显子9至12缺失。长距离PCR和测序表明存在14.7 kb的缺失事件。基于在第8内含子中的一个AluSp元件和第12内含子中的一个AluSx元件内鉴定出的缺失断点，设计了一种三引物PCR检测方法。单倍型分析证实了共同祖先。对cDNA的分析显示外显子8直接剪接到13，导致移码突变并预测BRCA1蛋白截短。
我们在5个不相关的家族中鉴定并描述了一种新的BRCA1大片段缺失——4个墨西哥裔家族和1个非洲及美洲原住民血统家族，提示可能存在美洲印第安人或混血起源的奠基者效应。在BRCA序列阴性的西班牙裔家族中，3.8%（106例中的4例）检测到这种BRCA1重排。对于序列阴性的高危西班牙裔患者，应考虑对这种突变进行检测。
