Letter to the Editor Diagnostic Hematology Identification of Mixed Lineage Leukemia Gene (MLL)/ MLLT10 Fusion Transcripts by Reverse Transcription- PCR and Sequencing in a Case of AML With a FISH- Negative Cryptic MLL Rearrangement

The mixed lineage leukemia gene (MLL) on chromosome 11q23 is a frequent target of chromosomal translocations and rear-rangements in childhood leukemia and adult therapy-related leukemia [1]. By using a commercially available dual-color FISH break-apart probe, almost all MLL rearrangements can be de-tected, including variant and cryptic forms [2-4]. We report a unique case of cryptic MLL rearrangement, in which the patient exhibited a karyotype that did not include t(10;11)(p12;q23) and FISH results did not reveal MLL break-apart signals; how-ever, molecular analysis by reverse transcription (RT)-PCR re-vealed a 388-bp amplicon corresponding to the MLL/MLLT10 fusion transcript. A 17-yr-old male was admitted to our hospital for evaluation and management of multiple palpable neck lymphadenopa-thies. Blasts accounted for approximately 94 % of cells on pe-ripheral blood smear. On bone marrow (BM) aspiration smear, 90.5 % of nucleated cells were blasts. Chromosomes were analyzed via GTG banding. Complex structural abnormalities were observed, and the karyotype was 46,XY,der(10)t(10;21)(p12;q21),der(12)del(12)(p11.2)add(12) (q24.2)[17]/46,XY[3] (Fig. 1). FISH analysis was performed ac-cording to the manufacturer’s instructions, including MLL (LS