The CREB-binding protein (CBP) is a large nuclear protein that regulates many signal transduction pathways and is involved in chromatin-mediated transcription. The translocation t(8;16)(p11;p13.3) consistently disrupts two genes: the CBP gene on chromosome band 16p13.3 and the MOZ gene on chromosome band 8p11. Although a fusion of these two genes as a result of the translocation is expected, attempts at detecting the fusion transcript by reverse transcriptase polymerase chain reaction (RT-PCR) have proven difficult; to date, only one inframe CBP/MOZ fusion transcript has been reported. We therefore sought other reliable means of detecting CBP rearrangements. We applied fluorescence in situ hybridization (FISH) and Southern blot analyses to a series of AML patients with a t(8;16) and detected DNA rearrangements of both the CBP and the MOZ loci in all cases tested. All six cases examined for CBP rearrangements have breakpoints within a 13 kb breakpoint cluster region at the 5′ end of the CBP gene. Additionally, we used a MOZ cDNA probe to construct a surrounding cosmid contig and detect DNA rearrangements in three t(8;16) cases, all of which display rearrangements within a 6 kb genomic fragment of the MOZ gene. We have thus developed a series of cosmid probes that consistently detect the disruption of the CBP gene in t(8;16) patients. These clones could potentially be used to screen other cancer-associated or congenital translocations involving chromosome band 16p13.3 as well.

Clonality of myeloid and lymphoid cell fractions obtained from peripheral blood (PB) or bone marrow (BM) of five patients with a myelodysplastic syndrome (MDS), was studied by combined immunophenotypic analysis and DNA in situ hybridization. This novel technique enables quantitative and direct analysis of cytogenetic alterations in nondividing cells of distinct cell lineages. Four patients with a trisomy 8 and one patient with a translocation (1;7) were studied. For cell lineage determination, antibodies specific for progenitor cells (CD34), myeloid cells (CD15), monocytes (63D3), T cells (CD3), and B cells (CD19,20,22) were used. In one patient with a trisomy 8, BM cells were available and the erythroid lineage could be studied. For detection of cytogenetic aberrations, we used chromosome- specific repetitive DNA probes. In three patients, all nonlymphoid cells carried the cytogenetic abnormality; in two patients, mosaicism within these lineages was suggested by the relative low numbers (35% to 55%) of aberrant cells. None of the T or B cells of the five patients carried the chromosomal aberrations. We conclude that combined immunophenotyping and in situ hybridization is a feasible technique to study lineage involvement. Our data suggest that the chromosomal aberrations studied in MDS are restricted to the myeloid lineages.

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Two patients with partial monosomy of the short arm of chromosome 8 are described. Their clinical features were very similar. Comparison with previously reported patients confirms the existence of an 8psyndrome. The importance of cytogenetic investigations in all infants with major congenital heart defect and facial dysmorphism or microcephaly or both is stressed.

An alphoid repetitive DNA (D8Z2) probe specific for the pericentromeric region of chromosome 8 was used to detect extra copies of chromosome 8 in bone marrow cells obtained from 10 patients with hematological disorders and five controls. Numerical aberrations of chromosome 8 were established by conventional banding techniques. Trisomy 8 was found in four patients with myelodysplastic syndrome (MDS) and three with acute myeloid leukemia (AML). Three additional patients with MDS exhibited an extra chromosome 8 in only one metaphase. In five of the seven trisomy cases, the presence of the trisomy 8 clone was confirmed by in situ hybridization (ISH). In one case of AML with trisomy 8, detected by GTG-banding, no significant numbers of cells containing three spots were found using the alphoid repetitive probe; however, hybridization with a chromosome 8-specific library revealed that the alleged extra chromosome 8 was a translocation chromosome containing only the long arm of chromosome 8. Due to a lack of material, it was not possible to achieve optimal ISH results on the trisomy 8 bone marrow cells of patient 7. In the three MDS patients with a single trisomy 8 metaphase, a slight, albeit significant, increase of trisomy 8 interphase cells was found with ISH. We conclude that this probe is useful for cytogenetic studies. Moreover, ISH, in general, is a powerful tool for precise classification of chromosomal aberrations and can also contribute significantly to the clinical evaluation of patients with hematological disorders.