Schematic showing the effect of 13q12.2 deletions on FLT3 expression in BCP-ALL. The novel regulatory enhancer DS3 normally lies far upstream of the FLT3 gene on chromosome 13q. In wild-type cells, DS3 and FLT3 occur in separate TADs and are therefore functionally insulated from one another in the genome. Recurrent 13q12.2 deletions in BCP-ALL eliminate the boundary between these 2 TADs, allowing the DS3 enhancer to contact FLT3 and activate its expression.