Chromosome 22 breakpoints in variant Philadelphia translocations and Philadelphia-negative chronic myeloid leukemia

The standard t(9;22)(q34;q11) found in Philadelphia (Ph) chromosome positive chronic myeloid leukemia (CML) involves a highly restricted (5.8 kb) chromosome 22 breakpoint cluster region (bcr), which results in the formation of a chimeric gene comprising exons from the 5' end of bcr and protooncogene c-abl coding sequences from chromosome 9. In a survey of 21 patients with hematologic and clinical features of CML we detected rearrangement of the chromosome 22 bcr by gene probe analysis in all cases, including 16 with a standard t(9;22), two with variant Ph translocations [t(10;22)(q26;q11);t(11;22)(p15;q11)], one with a complex Ph translocation [t(9;11;22)(q34;q13;q11)], one with a complex translocation and a masked Ph[t(9;14;22) (q34;q24;q11)], and one Ph-negative case with a t(1;9)(p32;q34). These observations further substantiate the suggestion that, despite karyotypic heterogeneity, a common underlying molecular lesion, the bcr-abl gene chimera, is involved in the disease pathogenesis of CML.     

Cytogenetic and molecular cytogenetic studies of a variant of t(21;22), ins(22;21)(q12;q21q22), with a deletion of the 3' EWSR1 gene in a patient with Ewing sarcoma

Ewing sarcoma is the second most common malignant bone tumor in children and young adults. Cytogenetic analysis to identify a common t(11;22)(q23;q12) or less frequently a t(21;22)(q22;q12) or t(7;22)(p22;q12) plays an important role in the confirmation of the clinical diagnosis. We report a case of a 10-year-old female who had extraskeletal Ewing sarcoma. Conventional cytogenetic analysis revealed that 11 out of 20 cells had a derivative chromosome 22, possibly due to an insertion of the long arm of the 21q21 approximately q22. This finding was confirmed by fluorescence in situ hybridization (FISH) utilizing whole chromosome paint probes specific for chromosomes 21 and 22. Hybridization utilizing LSI EWSR1, dual-color break-apart rearrangement probe unexpectedly revealed that the 3' EWSR1 gene was lost on the derivative chromosome 22. This finding suggests that the insertion of chromosome 21 is another mechanism that could lead to EWS-ERG gene fusion. To our knowledge, this is the first case report of an insertion of a segment of 21q21 approximately q22 into the long arm of 21q12 with a loss of a DNA segment around the breakpoint on the derivative chromosome 22 in Ewing sarcoma.     

Novel chromosome 16 abnormality--der(16)del(16) (q13)t(16;21)(p11.2;q22)--associated with acute myeloid leukemia.

Inversion of chromosome 16 is a common feature of acute myeloid leukemia (AML) M4, while t(16;21), although also associated with AML, appears to be a separate entity. We present a patient with myelodysplastic syndrome (MDS) who transformed to AML-M1. The karyotype was normal at diagnosis; at 15 months, hematological evidence of transformation was present, and repeat cytogenetics showed a novel rearrangement of one chromosome 16. Two breaks had occurred; one in the short arm at 16p11, with translocation of the segment distal to this onto chromosome 21q, and the other in the long arm at 16q22 with subsequent deletion of the segment from 16q22-->qter. Fluorescence in situ hybridization (FISH) confirmed the abnormalities detected by cytogenetics and excluded involvement of the AML1 gene on 21q22. While the 16q22 breakpoint was at the usual site for the inv(16), the 16p11 was not. The patient is more characteristic of t(16;21) than inv(16), and adds to the spectrum of chromosome 16 abnormalities in AML.