Pentasomy 8q in myelodysplasia

Acquired Robertsonian translocations are not rare events in acute leukemia and lymphoma

Robertsonian translocations are the most common constitutional structural abnormalities but are rarely reported as acquired aberrations in hematologic malignancies. The nonhomologous acrocentric rearrangements are designated as Robertsonian translocations, whereas the homologous acrocentric rearrangements are referred to as isochromosomes. Robertsonian rearrangements have the highest mutation rates of structural chromosome rearrangements based on surveys of newborns and spontaneous abortions. It would be expected that Robertsonian recombinations would be more common than suggested by the literature. A survey of the cytogenetics database from a single institution found 17 patients with acquired Robertsonian rearrangement and hematologic malignancies. This is combined with data from the literature for a total of 237 patients. All of the possible types of Robertsonian rearrangements have been reported in hematologic malignancies, with the i(13q), i(14q), and i(21q) accounting for nearly 60%. Complex karyotypic changes are seen in the majority of cases, corresponding with disease evolution. These karyotypes consistently show loss of chromosomes 5 and/or 7 in the myelocytic disorders, nonacrocentric isochromosomes, and centromeric breakage and reunion. However, nearly 25% of the acquired rearrangements were found as the sole abnormality or in addition to an established cytogenetic aberration. Most of these were the i(14q) with the myelodysplasia subtypes refractory anemia and chronic myelomonocytic leukemia.

Pentasomy 8q in therapy-related myelodysplastic syndrome due to cyclophosphamide therapy for fibrosing alveolitis

Trisomy 8/8q is a common cytogenetic event in myelocytic malignancies, ranging from myelodysplastic syndrome (MDS) to acute myelocytic leukemia (AML) to blastic transformation of chronic myelocytic leukemia. Isochromosome 8q results in the same gene dosage effect. Duplication of i(8q), resulting in pentasomy 8q, has been reported only in two cases of AML. A patient with fibrosing alveolitis on prolonged cyclophosphamide treatment developed therapy-related MDS. Karyotyping, FISH, and CGH analysis showed a duplicated i(8q) among other complex abnormalities. The clinical features of 11 cases of myelocytic leukemia with pentasomy and hexasomy 8/8q were summarized. Compared with trisomy and tetrasomy 8, significant features included reduced median survival (90 days), treatment refractoriness (even with transplantation), monocytic differentiation, trilineage dysplasia, and radiation or toxin exposure. Increasing copy numbers of chromosome 8/8q may therefore be a marker of advanced leukemic evolution, exposure to toxins, underlying myelodysplasia, and an overall poor prognosis.

Pentasomy 8q resulting from duplication of isochromosome 8q in chronic myelomonocytic leukemia

We report an interesting case of chronic myelomonocytic leukemia (CMML) with pentasomy 8q resulting from the duplication of isochromosome 8q in a 47-year-old male. His blood picture and myelogram showed CMML and the chromosome study, using R-banding and G-banding techniques, revealed a karyotype of 47,XY,-8,+i(8)(q10)x2. Dual-color fluorescence in situ hybridization (FISH) studies with a #8 centromeric probe and a locus-specific probe for C-myc gene completely confirmed the result of the conventional cytogenetic method. Reverse transcription polymerase reaction (RT-PCR) revealed no BCR/ABL fusion transcript. Hydroxyurea and 6-mercaptopurine therapy did not induce a complete remission and five months later he died of exacerbation of his disease. On reviewing another two cases with pentasomy 8q in the literature, we feel that pentasomy 8q, when present as a sole anomaly, may play a specific role in leukemogenesis and in determining the clinical characteristics such as monocytic involvement and poor prognosis.

Co-existence of alternative forms of 8q gain in cytogenetic clones of three patients with acute myeloid leukemia, pointing to 8q22 approximately 8qter as a region of biologic significance

Clonal trisomy 8 chromosome abnormalities can be detected in 15% of patients with acute myeloid leukemia (AML). The most common form of change is complete gain of the whole chromosome 8, followed by partial gains in unbalanced forms. The biologic consequences of trisomy 8 remain unclear, but a gene dosage effect is suspected. We report on three patients with AML who had alternative forms of chromosome 8 gain in their bone marrow cells. The partial gains resulted from a breakpoint in the chromosome band 8q22. This indicates that the region 8q22 to 8qter may be of particular pathogenetic importance.

Trisomy/ tetrasomy of chromosome 8 and +i(8q) as the sole chromosome abnormality in three adult patients with myelomonocytic leukemia

We report three cases of tetrasomy 8 associated with myeloid disease. Two patients had chronic myelomonocytic leukemia (CMMoL) and the other had acute monocytic leukemia (AML M5 FAB). Two patients had trisomy/tetrasomy chromosome 8 as the sole abnormality. The other patient with CMMoL had two normal 8 chromosomes plus one isochromosome 8q; this is the first case of long arm chromosome 8 tetrasomy without short arm 8 monosomy. This cytogenetic finding suggests the importance of the genes located in the long arms of chromosome 8.

Molecular genetics and cytogenetics of myeloproliferative disorders

The myeloproliferative disorders are believed to represent clonal malignancies resulting from transformation of a pluripotent stem cell. X-inactivation patterns of peripheral blood cells have been proposed as a useful diagnostic tool but this method is limited by the finding of a clonal X-inactivation pattern in a significant proportion of normal elderly women. There is no pathognomonic chromosomal abnormality associated with the myeloproliferative disorders. However, consistent acquired cytogenetic changes include del(20q), del(13q), trisomy 8 and 9 and duplication of segments of 1q, all of which have been observed at diagnosis or before cytoreductive therapy and therefore represent early lesions which contribute to the pathogenesis of these disorders. Although, the acquired molecular defects underlying most myeloproliferative disorders have not yet been elucidated, translocations associated with the rare 8p11 syndrome have permitted identification of a novel fusion protein. The role of a number of candidate genes in the other myeloproliferative disorders has also been studied, but no mutations have been identified so far. It is likely that a number of genes will be involved, given the varied phenotypes of the diseases. Identification of causal genes will be of considerable interest to both clinicians, who currently lack a specific and sensitive diagnostic test, and scientists interested in fundamental issues of stem cell behaviour.