QKI and pilocytic astrocytoma: In pilocytic astrocytomas (PAs), fusions of the NTRK2 gene, which encode for the tropomyosin receptor kinase B (TrkB) with either the transcriptional repressor nucleus Accumbens-associated protein 2 (NACC2), NACC2-NTRK2, or the pre-mRNA alternative splicing regulator Quaking homolog KH domain containing RNA binding (QKI), QKI-NTRK2, can induce MAPK pathway hyperactivity in a ligand-independent manner [53].