Fluorescent in situ hybridization for identifying cytogenetic abnormalities in inadequate and suboptimal specimens

Chronic idiopathic myelofibrosis (CIMF) resulting from a unique 3;9 translocation disrupting the janus kinase 2 (JAK2) gene

We report a case of t(3;9)(q21;p24) in a patient with chronic idiopathic myelofibrosis (CIMF), a chronic myeloproliferative disorder (CMPD), initially detected by G-banding and fluorescent in situ hybridization (FISH) in an unstimulated culture of peripheral blood. Subsequent cytogenetic studies of bone marrow aspirates showed the presence and persistence of the same translocation. No additional cytogenetic abnormalities were found. This appears to be a unique translocation that has not been previously reported in the English literature, although both breakpoints, 3q21 and 9p24, are well known cancer-related breakpoints. The former is the mapped location of the ribophorin 1 (RPN1) gene, whereas the latter is the mapped location of the janus kinase 2 (JAK2) gene. This raises the possibility that disruption of one or both loci at the breakpoints of the presently described structural chromosomal rearrangement may be the primary event leading to the initiation and development of the hematopoietic disorder in this patient. It is not unreasonable to hypothesize that the juxtaposition of the RPN1 gene on 3q21 with the JAK2 gene on 9p24 leads to enhanced JAK2 activity. Additional studies will be needed to provide further support for or to disprove this hypothesis. To the best of our knowledge, this is the first reported case of CIMF associated with a reciprocal 3;9 translocation with the 3q21 and 9p24 breakpoints. The elucidation of the mechanism of leukemogenesis in CIMF may one day lead to successful targeted therapy in this hematopoietic disorder. It may also shed additional light on the diagnosis, prognosis and treatment of certain other cancers with similar genetic etiologies.

Cytogenetic study of a patient with infant acute lymphoblastic leukemia using GTG-banding and chromosome painting

Numerical and structural chromosomal abnormalities occur in up to 90% of cases of childhood acute lymphoblastic leukemia (ALL). Two-thirds of these abnormalities are recurrent. The most common abnormalities are pseudodiploidy and t(1;19), occurring 40 and 5-6% of the time. Hyperdiploidy has the best prognosis, with an 80-90% 5-year survival. The 4;11 translocation has the worst prognosis, with a 10-35% 5-year survival. We report a patient with infant acute lymphoblastic leukemia and nonrecurrent rearrangements of chromosomes 10 and 11. Structural rearrangements between chromosomes 10 and 11 have been observed in 0.5% of all cases of childhood ALL with cytogenetic abnormalities. The identification of the apparently unique structural abnormalities was achieved using fluorescent in situ hybridization (FISH) with chromosome 10- and chromosome 11-specific painting probes as an adjunct to conventional cytogenetics. As is often the case, suboptimal preparations often preclude unequivocal identification of complex rearrangements by conventional banding techniques. The cytogenetic diagnosis of our patient was established as 46,XY, der(10)-t(10;11)(p15;q14)t(10;11)(q25;p11), der(11)t(10;11)(p15;q14)t(10;11)-(q25;p11). The benefits of FISH serve to increase the resolution of detection for chromosomal abnormalities and the understanding of the pathogenic mechanisms of childhood ALL.

Discordant detection of monosomy 7 by GTG-banding and FISH in a patient with Shwachman-Diamond syndrome without evidence of myelodysplastic syndrome or acute myelogenous leukemia

The myelodysplastic syndromes (MDS) are a group of hematologic disorders commonly affecting elderly persons and often leading to acute myelogenous leukemia (AML). Although rare in children, when MDS does occur, it is frequently part of a congenital disorder such as Shwachman-Diamond syndrome (SDS). Monosomy 7 and/or deletion of part or all of 7q are poor prognostic signs in MDS and AML, although the pathophysiologic relationship between this finding and MDS or AML is unclear. Shwachman-Diamond syndrome is an inherited illness characterized by exocrine pancreatic insufficiency and by congenital neutropenia. Patients with SDS are at increased risk of developing myelodysplastic syndrome (MDS) and acute myelogenous leukemia (AML). Because monosomy 7 is a poor prognostic sign in MDS and AML, establishing its presence is important. However, different methods of detection of monosomy 7 may lead to different results in some patients. We present the case of a 10-year-old girl known to have SDS, who had a bone marrow aspiration and biopsy done to rule out MDS and AML. By light microscopy, the patient's bone marrow was unremarkable. GTG-banding showed the following karyotype: 45,XX,-C[3]/47,XX,+C[1]/46,XX[45]. Fluorescence in situ hybridization (FISH) was performed with a chromosome 7-specific alpha-satellite probe (D7Z1). Almost all (373 of 376) cells exhibited only one chromosome 7 signal. A second marrow aspiration done 6 months later showed an essentially normal karyotype by GTG-banding. Fluorescence in situ hybridization with the same chromosome 7 probe showed 230 of 250 cells to be monosomic for chromosome 7. A whole chromosome 7 painting probe demonstrated disomy for chromosome 7 in 90 of 90 cells; however, subtle heteromorphism in the centromeric regions of the 2 copies of chromosome 7 was noted in some cells. This case demonstrates that FISH and GTG-banding can give discordant results, that the two should be viewed as complementary technologies, and that both have a place in a full karyotypic analysis. Furthermore, this case demonstrates for the first time that heteromorphism and/or subtle structural abnormalities of chromosome 7, previously associated with MDS and AML, can exist without clinical or morphologic signs of these illnesses. It will be of interest to further study the relationship, if any, between SDS and various structural abnormalities of chromosome 7 in MDS and AML, and to elucidate the molecular mechanisms of pathogenesis, physiology, and treatment of these disorders.