Morphology and TTMV integration structure of our case. (A) A peripheral blood (PB) smear from our patient, stained with Wright-Giemsa, showing circulating promyelocytic blasts with abundant azurophilic granules. (B) Alignment of unique sequencing reads from PB from our patient. Reads shown originated in RARA exon 3, where our CRISPR guide is designed to cut. Nine of 26 unique reads (35%) covering the region of interest showed an insertion of ∼2.4 kb (framed in red). (C) The RARA gene with the TTMV insertion between exons 2 and 3. Blocks represent exons, joined by lines showing introns. Empty blocks represent untranslated regions. The red bar (3.4 kb) is positioned to mark the whole size of the integrated TTMV; the red block is the fragment of the insertion that we could prove was transcribed in our patient. The locations of primers used in panels D and E are marked (AN_5_F and RARA3_R). (D) Agarose gel 2% stained with ethidium bromide showing the product of amplification of the patient’s PB RNA after reverse transcription and amplification with primers designed to target the insertion and RARA exon 3. First lane: 100-bp DNA ladder; second lane: our patient; third lane: the no-template control. The expected product size was 654 bp. The actual product size was closer to 600 bp, as an 84-bp fragment of the insertion was not in the transcribed product. (E) A Sanger sequencing chromatograph, showing the sequence of TTMV ORF2 adjoining RARA exon 3 with a small (14 bp) intron sequence preserved. The cartoon in panel C was generated with Worm-web (http://wormweb.org/exonintron).