Hyperdiploidy with trisomy 9 and deletion of the CDKN2A locus in T-cell acute lymphoblastic leukemia.

We describe the rare finding of a T-cell acute lymphoblastic leukemia (T-ALL) and a pretreatment bone marrow karyotype mosaic for four distinct cell lines in a 4-year-old boy. G-banding analysis of metaphase cells identified a hyperdiploid cell line (52 chromosomes) trisomic for chromosomes 6, 9, 11, 13, 19, and 22. Fluorescence in situ hybridization (FISH) analysis demonstrated that these hyperdiploid cells were missing all three copies of the CDKN2A locus (alias p16/Ink4) at 9p21.

Down syndrome with low hypodiploidy in precursor B-cell acute lymphoblastic leukemia.

We describe the rare finding of a 33-month-old child neonatally diagnosed with Down syndrome, who presented with pre-B acute lymphoblastic leukemia (ALL) with a pretreatment bone marrow karyotype in which a low hypodiploid cell line (38 chromosomes) was identified in 17/19 cells studied. The abnormal cell line retained the extra constitutional chromosome 21. Hypodiploidy (loss of one or more chromosomes) is seen in approximately 5% of all childhood pre-B ALL cases and in approximately 2.