LSI ETV6/RUNX1 ES Dual Color Probe revealed increased signals of RUNX1 (red). (A) An interphase cell and metaphase cell from case 6. The cluster of red signals indicates amplification of RUNX1 on the abnormal chromosome 21. (B) An interphase cell from case 10. (C) Metaphase FISH analysis from case 10 confirms that the clustered red signals are on one chromosome (arrow).