Kehrer-Sawatzki H, Häussler J, Krone W, Bode H, Jenne D E, Mehnert K U, Tümmers U, Assum G
Abteilung Humangenetik, Ulm, Germany.
Hum Genet. 1997 Feb;99(2):237-47. doi: 10.1007/s004390050346.
A reciprocal t(17;22)(q11.2;q11.2) was found in a female patient with neurofibromatosis type 1 (NF1) and in her affected daughter. Sequence analysis of cloned junction fragments traversing the breakpoints allowed the identification of the structures involved in the rearrangement. Aberrant bands in Southern hybridizations of restriction enzyme-digested DNA of the patient pointed to the disruption of the NF1 gene in intron 31. Semispecific polymerase chain reaction analysis of the genomic DNA of the patient with the specific primer anchored at NF1 exon 31 was used to obtain the breakpoint-spanning fragment of the derivative chromosome 17. The intron 31 sequence turned out to be interrupted within a large irregular (AT) repeat. The chromosome 22-derived sequence of the der(17) junction fragment allowed us to identify cosmids of the corresponding region from a chromosome 22 specific cosmid library. With the support of the breakpoint-spanning cosmids, the chromosome 22 region upstream of the fragment carried by the der(17) was characterized. Primers deduced from the sequence of this upstream region were used in combination with a primer in NF1 intron 31 distal to the breakpoint on chromosome 17 to amplify the der(22) junction fragment. The structure of the junction sequences suggested that the translocation had arisen by unequal homologous recombination between (AT)-rich repeats on chromosome 22 and on chromosome 17 in intron 31 of the NF1 gene. However, our data support the assumption of additional rearrangements prior to, or in the course of, the recombination event, leading to a loss of the sequences between the involved (AT) repeats on chromosome 22. In the direct vicinity of these (AT) repeats, two members of a previously undescribed low-copy repetitive sequence have been found, copies of which are also present on human chromosome 13.
在一名患有1型神经纤维瘤病（NF1）的女性患者及其患病女儿中发现了相互易位t(17;22)(q11.2;q11.2)。对跨越断点的克隆连接片段进行序列分析，得以鉴定参与重排的结构。患者经限制性内切酶消化的DNA进行Southern杂交时出现的异常条带表明NF1基因在内含子31处发生了断裂。使用以NF1外显子31为锚定的特异性引物对患者基因组DNA进行半特异性聚合酶链反应分析，以获得衍生染色体17的跨越断点片段。结果发现内含子31序列在一个大的不规则（AT）重复序列内被打断。der(17)连接片段中来自染色体22的序列使我们能够从染色体22特异性黏粒文库中鉴定出相应区域的黏粒。在跨越断点的黏粒的支持下，对der(17)所携带片段上游的染色体22区域进行了表征。从该上游区域序列推导的引物与位于染色体17断点远端的NF1内含子31中的引物联合使用，以扩增der(22)连接片段。连接序列的结构表明，该易位是由NF1基因内含子31中染色体22和染色体17上富含（AT）的重复序列之间的不等位同源重组产生的。然而，我们的数据支持在重组事件之前或过程中发生了额外重排的假设，导致染色体22上相关（AT）重复序列之间的序列丢失。在这些（AT）重复序列的紧邻区域，发现了一个先前未描述的低拷贝重复序列的两个成员，其拷贝也存在于人类染色体13上。
