Tetrasomy 21 as a sole chromosome abnormality in acute myeloid leukemia: fluorescence in situ hybridization and spectral karyotyping analyses

We report a case of acute myeloid leukemia with tetrasomy 21 as the sole chromosome abnormality in a constitutionally normal patient. Tetrasomy 21 was observed at presentation, disappeared in remission, but reappeared in recurrence of the disease. Fluorescence in situ hybridization analysis using a probe specific for the AML1 gene showed four distinct signals in 82.4% and three signals in 10.8% of interphase nuclei, although conventional G-banding revealed tetrasomy 21 alone in mosaicism with normal karyotype. Spectral karyotyping further confirmed the presence of extra copies of chromosome 21. Tetrasomy 21 as the only anomaly is relatively rare in patients with hematologic disorders other than Down syndrome, and to our knowledge has been reported previously in only seven cases. In a review of the literature, tetrasomy 21 as the only anomaly may be associated with myeloid disorders, although simultaneous numeric abnormalities other than chromosome 21 have been reported in acute lymphoblastic leukemia with hyperdiploid karyotype.