Second-site mutation in the Wiskott-Aldrich syndrome (WAS) protein gene causes somatic mosaicism in two WAS siblings.
Second-site mutation in the Wiskott-Aldrich syndrome (WAS) protein gene causes somatic mosaicism in two WAS siblings.
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DOI：
10.1172/jci15485
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发表时间：
2003-05
期刊：
影响因子：
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通讯作者：
T. Wada;A. Konno;S. Schurman;E. Garabedian;S. Anderson;M. Kirby;D. Nelson;F. Candotti
中科院分区：
文献类型：
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作者：
T. Wada;A. Konno;S. Schurman;E. Garabedian;S. Anderson;M. Kirby;D. Nelson;F. Candotti
在几种遗传性疾病中已经发现了由真回复突变或第二位点突变引起的回复突变嵌合现象。回复突变体的发生被认为是罕见的，基本的遗传机制仍然是未知的。在这里，我们描述了两个兄弟与Wiskott-Aldrich综合征（WAS）的躯体嵌合体。在这个家族中引起疾病的原始突变是WAS蛋白（WASP）基因中的单碱基插入（1305 insG），其导致移码并消除蛋白质表达。然而，这两名患者的T细胞中都有WASP的表达，这些T细胞被证明携带第二位点突变，导致从核苷酸1299到1316的19个核苷酸缺失。这种缺失消除了原始突变的影响，并恢复了WASP阅读框架。体外表达研究表明，由第二位点突变编码的突变蛋白是表达和功能性的，因为它能够与细胞伴侣结合并介导T细胞受体/CD 3下调。这些观察结果与WASP表达淋巴细胞的体内选择优势的证据一致。分子生物学分析表明，缺失的周围序列包含两个4-bp的直接重复序列，并且在缺失的片段内可以由五个GC对形成发夹结构。这些研究结果强烈表明，滑动错配的原因，这第二个网站的突变和选择性积累的WASP表达T淋巴细胞导致这些患者的回复突变嵌合体。
Revertant mosaicism due to true back mutations or second-site mutations has been identified in several inherited disorders. The occurrence of revertants is considered rare, and the underlying genetic mechanisms remain mostly unknown. Here we describe somatic mosaicism in two brothers affected with Wiskott-Aldrich syndrome (WAS). The original mutation causing disease in this family is a single base insertion (1305insG) in the WAS protein (WASP) gene, which results in frameshift and abrogates protein expression. Both patients, however, showed expression of WASP in a fraction of their T cells that were demonstrated to carry a second-site mutation causing the deletion of 19 nucleotides from nucleotide 1299 to 1316. This deletion abrogated the effects of the original mutation and restored the WASP reading frame. In vitro expression studies indicated that mutant protein encoded by the second-site mutation was expressed and functional, since it was able to bind to cellular partners and mediate T cell receptor/CD3 downregulation. These observations were consistent with evidence of in vivo selective advantage of WASP-expressing lymphocytes. Molecular analysis revealed that the sequence surrounding the deletion contained two 4-bp direct repeats and that a hairpin structure could be formed by five GC pairs within the deleted fragment. These findings strongly suggest that slipped mispairing was the cause of this second-site mutation and that selective accumulation of WASP-expressing T lymphocytes led to revertant mosaicism in these patients.