Here we describe a rare case of congenital KMT2Ar ALL presenting with co-occurring IKZF1 gene fusions and a predictably aggressive disease trajectory. We report for the first time, the novel IKZF1::TUT1 and KDM2A::IKZF1 gene fusions. Rearrangements in-volving KMT2A are commonly retained in relapsed infant ALL, however, in this case the KMT2A::AFF1 gene fusion did not appear to be the lesion driving leukemic relapse. Instead, our data suggest that relapse was driven by IKZF1::TUT1. This gene fusion remained in all samples investigated, including the on-blinatumomab therapy sample taken immediately prior to relapse. Conversely, the KMT2A::AFF1 gene fusion was only detected in the diagnosis and refractory post-induction samples highlighting a key role for IKZF1::TUT1 in disease pathogenesis. Intriguingly, both IKZF1 gene fusions are predicted to be out-of-frame, however, our data demonstrate the IKZF1 gene is still expressed. This is not unprecedented and it has previously been observed that out-of-frame fusions can cause transcriptional activation/repression of genes involved in the ... (Show More)

Here we describe a rare case of congenital KMT2Ar ALL presenting with co-occurring IKZF1 gene fusions and a predictably aggressive disease trajectory. We report for the first time, the novel IKZF1::TUT1 and KDM2A::IKZF1 gene fusions. Rearrangements in-volving KMT2A are commonly retained in relapsed infant ALL, however, in this case the KMT2A::AFF1 gene fusion did not appear to be the lesion driving leukemic relapse. Instead, our data suggest that relapse was driven by IKZF1::TUT1. This gene fusion remained in all samples investigated, including the on-blinatumomab therapy sample taken immediately prior to relapse. Conversely, the KMT2A::AFF1 gene fusion was only detected in the diagnosis and refractory post-induction samples highlighting a key role for IKZF1::TUT1 in disease pathogenesis. Intriguingly, both IKZF1 gene fusions are predicted to be out-of-frame, however, our data demonstrate the IKZF1 gene is still expressed. This is not unprecedented and it has previously been observed that out-of-frame fusions can cause transcriptional activation/repression of genes involved in the fusions leading to increases or decreases of their expression and the as-sociated functional outcomes.

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