Pathogenetic implication of fusion genes in acute promyelocytic leukemia and their diagnostic utility

Acute promyelocytic leukemia (APL) has been recognized as a discrete subset of hematopoietic malignancies constituting approximately 10% of acute myeloid leukemia cases. The hallmark reciprocal chromosomal translocation t(15;17) involving fusion between the retinoic acid receptor (RARα) gene and promyelocytic leukemia (PML) gene is a characteristic feature in APL which consequently results in the emergence of PML-RARα chimeric gene. This gene has been substantiated to be responsible for cellular transformation and is a prime target of all-trans-retinoic acid (ATRA) as well as arsenic-trioxide (ATO) therapy. Since this initial discovery, about 10 diverse translocation partner genes of RARα have been reported that result in variant APL forms strongly suggesting that disruption of RARα underlies its pathogenesis. The nature of the fusion partner has a significant bearing upon disease characteristics including sensitivity to retinoids and ATO and thereby underpins the need for rapid and accurate diagnosis and also demands a highly specific treatment approach. In this article we laid emphasis on the rearrangement of the RARα gene and its different fusion partners resulting in variant forms of APL, their implication in underlying molecular pathogenesis of APL and also the different diagnostic modalities that should be employed for their rapid and accurate diagnosis.