Δ-CRLF2 can be detected together with IKZF1 deletion in Ph-negative ALL patients and with JAK mutations (JAK1 or JAK2) or IL7R mutations; furthermore, they are identified in roughly 50% of children with Down syndrome;55,58 although some contrasting results have been reported, its presence correlates with an overall poor outcome.54,55. Here, JAK1 is linked to acute lymphoblastic leukemia.