Karyotype and FISH analysis in patient 1. (A). Cytogenetic analysis of peripheral blood abnormal cell showing duplication of 7p14-p15 (black arrow) and 3 copies of chromosome 21 (red arrow). (B). FISH on peripheral blood using probes specific for ETO (orange) and RUNX1 (green) genes. Note the presence of one strong and one dim green signal in the metaphase and lower left interphase nucleus confirming the constitutional RUNX1 deletion. In the lower right interphase nucleus there are 1 strong and 2 “dim” RUNX1 signals, representing a trisomy 21 cell line with duplication of the deleted chromosome 21.