Fligman I, Lonardo F, Jhanwar S C, Gerald W L, Woodruff J, Ladanyi M
Department of Pediatrics, Memorial Sloan-Kettering Cancer Center, New York, New York 10021, USA.
Am J Pathol. 1995 Dec;147(6):1592-9.
The translocation t(X;18)(p11;q11) is seen in > 80% of synovial sarcomas (SS) with informative karyotypes. The breakpoints of the t(X;18) have been cloned and shown to involve two novel genes, SSX (at Xp11) and SYT (at 18q11), which produce a chimeric SYT-SSX transcript as a result of the translocation. Recently, SSX has been shown to be duplicated, with both copies, SSX1 and SSX2, located within distinct subregions of Xp11. We performed a reverse transcriptase polymerase chain reaction (RT-PCR) assay for both chimeric SYT-SSX transcripts in a series of 35 SS (29 monophasic, 6 biphasic) to assess its usefulness in molecular diagnosis and to evaluate the incidence of molecular variants. Of the 35 cases, 29 (83%) showed a specific SYT-SSX RT-PCR product, using a consensus primer for SSX1 and SSX2 Upon excluding three negative cases that had poor quality RNA, the proportion of positives rose to 91% (29/32). The 29 positive cases were further studied using primers specific for either SSX1 or SSX2; 19 cases were positive for SYT-SSX1 and 10 for SYT-SSX2. The relationship of histological subtype (monophasic versus biphasic) to SSX1 or SSX2 involvement was not statistically significant. In a single histologically unremarkable monophasic SS, a slightly larger SYT-SSX2 RT-PCR product was observed. Sequencing of this novel variant showed a 129-bp segment inserted between the usual SYT and SSX2 fusion points, of which 126 bp were derived from a more proximal (5') portion of SSX2 The 3 bp immediately 5' to the fusion point could not be assigned to either SYT or SSX2 and may represent an insertion-deletion or a cryptic splicing event. This fragment maintains the reading frame of the chimeric product and encodes a predicted protein larger by 43 amino acids, which nevertheless replaces the region homologous to the transcriptional repression domain Kruppel-associated box, recently recognized in the 5' portion of the SSX genes, with all but the 3' end of the SYT transcript. Thus, a diagnosis of SS may be confirmed in > 90% of cases using RT-PCR detection of the chimeric transcript resulting from the t(X;18), and the incidence of molecular variants appears low.
在核型信息明确的滑膜肉瘤（SS）中，超过80%可见易位t(X;18)(p11;q11)。t(X;18)的断点已被克隆，发现涉及两个新基因，SSX（位于Xp11）和SYT（位于18q11），该易位导致产生嵌合的SYT-SSX转录本。最近研究显示SSX存在重复，两个拷贝SSX1和SSX2位于Xp11的不同亚区域。我们对35例SS（29例单相型、6例双相型）进行逆转录聚合酶链反应（RT-PCR）检测嵌合的SYT-SSX转录本，以评估其在分子诊断中的实用性并评估分子变异的发生率。35例病例中，29例（83%）使用针对SSX1和SSX2的共有引物显示出特异性的SYT-SSX RT-PCR产物。排除3例RNA质量差的阴性病例后，阳性比例升至91%（29/32）。对29例阳性病例进一步使用针对SSX1或SSX2的特异性引物研究；19例为SYT-SSX1阳性，10例为SYT-SSX2阳性。组织学亚型（单相型与双相型）与SSX1或SSX2参与情况的关系无统计学意义。在1例组织学表现不明显的单相型SS中，观察到一个稍大的SYT-SSX2 RT-PCR产物。对这个新变异进行测序显示，在通常的SYT和SSX2融合点之间插入了一个129 bp的片段，其中126 bp来自SSX2更靠近5'端的部分。紧挨着融合点5'端的3 bp无法确定属于SYT还是SSX2，可能代表一个插入缺失或隐蔽剪接事件。该片段保持了嵌合产物的阅读框，编码一个预测的蛋白质，比原来大43个氨基酸，不过用SYT转录本除3'端外的所有部分取代了SSX基因5'端最近发现的与转录抑制结构域Kruppel相关盒同源的区域。因此，使用RT-PCR检测由t(X;18)产生的嵌合转录本，在超过90%的病例中可确诊SS，且分子变异的发生率似乎较低。
