9号环状染色体综合征的荧光原位杂交分析

Analysis of ring chromosome 9 syndrome with fluorescence in situ hybridizations

目的对1例9号环状染色体综合征患儿进行细胞分子遗传学分析，探索9号环状染色体与临床表型的关系。方法采用染色体G显带核型分析和TelVision 9p探针和TelVision 9q探针进行双色荧光原位杂交，识别和定位1例9号环状染色体患儿。结果患儿核型为45，X，-9／46，XX，r（9）（p24q34）／46，XX，r（9；9）（p24q34；p24q34）（4／92／4）。双色荧光原位杂交显示9号环状染色体上没有杂交信号，提示9号环状染色体短臂末端缺失片段至少有115kb，长臂末端缺失片段至少有95kb。与其它报道的环状9号染色体综合征、9号染色体短臂和长臂部分单体综合征相比，本例患者兼有环状9号染色体综合征的临床特征以及9号染色体短臂和长臂部分单体综合征的一些特征。结论由于缺失的断裂点之间亚显微结构的不同、环的不稳定性、基因与表型相互作用以及胎儿环境条件的不同等原因，具有相同断裂点的9号环状染色体综合征患者可以有不同的临床表型，单倍基因剂量不足对临床表型发挥了重大作用。

Objective To investigate the mechanism of the ring chromosome 9 formation by cytogenetic analysis of one case affected with ring chromosome 9 syndrome. Methods Routine chromosome GTG-binding analysis and dual color fluorescence in situ hybridization （FISH） with TelVision 9p and 9q probes were applied to characterize the case. Results The G-binding revealed that the patient had ring chromosome 9 with the following karyotype： 45,X,-9/46,XX, r（9）（p24q34）/46,XX, r（9;9）（p24q34; p24q34）[4/92/4]. The dual color FISH analysis with TelVision 9p and TelVision 9q probes failed to detect a hybridization signal on the ring chromosome in the case, which indicated that at least 115 kb were deleted on the terminal 9p and 95 kb were deleted on the terminal 9q. Comparing to the cases reported in the literatures, our patient shared some common features of the 9p- and 9q syndrome. Conclusion The clinical features of patients with identical r（9） breakpoints present variable phenotypes. The possible cause might be the submicroscopic variation in the deletion breakpoints, variation in the ring stability, the modification of the expression of the deleted by the individual＇s genetic background, or the effect of changes in the fetal environment. The haploinsufficieney of genes located in the deleted regions may play critical roles in the patient phenotype as well.