Acute promyelocytic leukemia with a cryptic insertion of RARA into PML on chromosome 15 due to uniparental isodisomy: A case report

Acute promyelocytic leukemia is a myeloid disorder that is characterized by the specific t(15;17) variant in ~98% of cases. The typical hypergranular and microgranular or hypogranular types exist, and are frequently associated with disseminated intravascular coagulopathy. Rare cases of promyelocytic leukemia-retinoic acid receptor α (PML-RARA) fusion without the reciprocal RARA-PML have been reported in cytogenetically normal samples. Conversely, fluorescence in situ hybridization (FISH) analysis has revealed a cryptic insertion of the RARA gene into the PML gene on chromosome 15. The current study reports a unique case with a normal karyotype and molecular evidence of the PML-RARA short isoform 3-fusion transcript, with FISH analysis revealing two fusion signals on the two copies of chromosome 15, but absence of the reciprocal on the two copies of chromosome 17. This finding raised the hypothesis of chromosome 15 uniparental isodysomy as consequence of normal chromosome 15 loss and duplication of the rearranged chromosome, as supported by polymorphic loci molecular analysis. The clinical, cytogenetic and molecular characterization of this case are presented and discussed in the present study.