Acute promyelocytic leukemia (APL), a subset of acute myeloid leukemia (FAB-M3), is cytogenetically characterized by the non-random, balanced t(15;17)(q22;q11,2-21) chromosome translocation. The chromosome 17 breakpoint occurs consistently in the second intron region of the structural retinoic acid receptor alpha (RARα) gene. RARα is a member of a nuclear receptor superfamily, and its disruption is thought to be directly linked to the interruption of normal myeloid differentiation. A transcription factor gene (PML1) is situated at the chromosome 15 breakpoint region. The chromosome 15 breakpoint can occur in intron 3 of the PML1 gene or in a downstream breakpoint region consisting of variable breakpoints in exon/intron 6. The t15;17 translocation generates a PML/RARα chimeric gene which is transcribed as a fusion PML/RARα mRNA. Detection of t(15;17) or its consequence, the fusion PML/RARα mRNA, is critical for patients with suspected APL. Its presence is the best predictor of a favorable response to retinoids, such as all-trans retinoic acid (ATRA), in combination with chemotherapy.
Quantification of expression of the t(15;17) PML/RARα chromosomal translocation is done on for confirmation of clinical diagnosis and monitoring of treatment efficacy.
The presence of the PML/RARα mRNA in a patient’s bone marrow or peripheral blood is detected using a real-time quantitative PCR to detect transcript levels of PML/RARα at breakpoints in intron 3 or inron/exon 6 of PML and exon 3 of RARα. We quantify transcript levels with relative quantification using a homogeneous cell line (UF1 or NB4) as the calibrator
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