Double minutes (dmin) and homogeneously staining regions (hsr) in myeloid disorders: a new case suggesting that dmin form hsr in vivo.

We describe a case of an 87-year-old woman with myelodysplastic syndrome (MDS) in transformation. At presentation, the patient suffered from refractory anemia with excess of blasts (RAEB). The karyotype showed a clone with 3 to >20 double minutes (dmin) that were MYC-positive and, in addition, a cryptic deletion of MYC on one of the chromosome 8 homologs. The dmin varied both in size and in fluorescence intensity for the MYC probe following FISH. After six months, the disease had progressed to refractory anemia with excess of blasts in transformation (RAEBT). The corresponding karyotype showed a second cell line with two markers that appeared like rings and, again, a cryptic MYC deletion on one of the chromosome 8 homologs. The markers contained centromeres and amplified MYC sequences. The deletion of MYC on one of the chromosome 8 homologs and the variable sizes and intensities of the dmin supports an episome model for dmin formation. Chronologically, the MYC-positive dmin appeared first, followed by the appearance of MYC-positive marker chromosomes, suggesting that the dmin may have evolved to form homogeneously staining regions (hsr) in vivo.