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 haploinsufficiency of genes located in the deleted regions may play critical roles in the patient phenotype as well.