Xie Fei, Wang Xuefeng, Cooper David N, Chuzhanova Nadia, Fang Yi, Cai Xiaohong, Wang Zhenyi, Wang Hongli
Shanghai Institute of Hematology, Ruijin Hospital, Shanghai Jiaotong University, China.
Blood Cells Mol Dis. 2006 May-Jun;36(3):385-91. doi: 10.1016/j.bcmd.2006.03.003. Epub 2006 May 11.
von Willebrand disease (VWD) type 3 is characterized by extremely low levels of von Willebrand factor (VWF) in plasma. To date, only 11 examples of gross deletions have been reported for the VWF gene and the underlying mutational mechanisms remain unclear. A Chinese patient with type 3 VWD was studied to elucidate the underlying mechanism of mutagenesis.
PCR was designed to amplify across the putatively deleted region of genomic DNA from the patient and his parents to locate the deletion breakpoints. In silico analysis was then performed to search for repetitive sequence elements, recombination-associated motifs, and scaffold/matrix attachment regions (S/MARs).
A novel homozygous gross deletion of the VWF gene, which removes some 61044 bp DNA between introns 5 and 16, was identified in the patient. The deletion junctions were flanked by highly homologous Alu repeats in inverted orientation. These repeats could thus have potentiated the formation of a stem-loop structure thereby bringing the breakpoints into close proximity. A number of recombination-associated motifs were noted in close proximity to both deletion breakpoints. Both the 5' and 3' breakpoints were located in, or near, regions with a high propensity to form S/MARs.
We report the first example of an Alu-mediated VWF gross gene deletion. Since a number of recombination-associated motifs were also identified in the vicinity of the breakpoints, it may be that multiple sequence elements have acted in concert to give rise to this deletion event.
3型血管性血友病（VWD）的特征是血浆中血管性血友病因子（VWF）水平极低。迄今为止，VWF基因仅报道了11例大片段缺失，其潜在的突变机制仍不清楚。对一名中国3型VWD患者进行研究以阐明诱变的潜在机制。
设计聚合酶链反应（PCR）以扩增患者及其父母基因组DNA的假定缺失区域，以定位缺失断点。然后进行电子分析以搜索重复序列元件、重组相关基序和支架/基质附着区域（S/MARs）。
在患者中鉴定出一种新的VWF基因纯合大片段缺失，该缺失去除了内含子5和16之间约61044 bp的DNA。缺失连接处两侧是反向的高度同源Alu重复序列。因此，这些重复序列可能增强了茎环结构的形成，从而使断点靠近。在两个缺失断点附近都发现了许多重组相关基序。5'和3'断点均位于易于形成S/MARs的区域内或附近。
我们报道了第一例Alu介导的VWF基因大片段缺失。由于在断点附近也鉴定出许多重组相关基序，可能是多个序列元件共同作用导致了这一缺失事件。
