Biologic features of the K666N mutation in SF3B1. (A) Comutation distribution of SF3B1^MUT AML patients shows a similar genetic landscape between K666N and other SF3B1 mutations, although RUNX1 and FLT3 mutations were higher in SF3B1^K666N patients. SRSF2 was also included, despite not being sequenced in all samples, because of its increased comutation in SF3B1^K666N MDS-RS (supplemental Figure 3). *P < .05, Fisher’s exact test. (B) Analysis of RNA-seq performed on isogenic Nalm6 cells by Darman et al shows that missplicing of some junctions is increased in all mutant cells (left panel), whereas others are increased in cells with K700E and H662Q, but not K666N, mutations (right panel). (C) Use of a single competitive end point PCR (upper panel) to validate distinct missplicing in independent cell populations with SF3B1 mutation, including SF3B1^K700E HNT34 AML cells, SF3B1^K666N MUTZ3 AML cells, wild-type CMLT1 and KG1 leukemia cells, and isogenic Nalm6 controls (lower panel). (D) Use of separate noncompetitive quantitative PCRs (qPCRs; upper panel) to further validate distinct missplicing in PHGDH (lower left panel) and COPS2 (lower right panel). *P < .05, Student t test.