Isodicentric X chromosomes involving the Xq13 breakpoint in myelodysplasia and acute nonlymphocytic leukemia

Loss of ABCB7 gene: pathogenesis of mitochondrial iron accumulation in erythroblasts in refractory anemia with ringed sideroblast with isodicentric (X)(q13)

An isodicentric (X)(q13) (idicXq13) is a rare, acquired chromosomal abnormality originated by deletion of the long arm from Xq13 (Xq13-qter), and is found in female patients with hematological disorders involving increased ringed sideroblasts (RSs), which are characterized by mitochondrial iron accumulation around the erythroblast nucleus. The cause of increased RSs in idicXq13 patients is not fully understood. Here, we report the case of a 66-year-old female presenting with refractory anemia with ringed sideroblasts (RARS), and idicXq13 on G-banded analysis. We identify the loss of the ABCB7 (ATP-binding cassette subfamily B member-7) gene, which is located on Xq13 and is involved in mitochondrial iron transport to the cytosol, by fluorescent in situ hybridization (FISH) analysis and the decreased expression level of ABCB7 mRNA in the patient's bone marrow cells. Further FISH analyses showed that the ABCB7 gene is lost only on the active X-chromosome, not on the inactive one. We suggest that loss of ABCB7 due to deletion of Xq13-qter at idicXq13 formation may have contributed to the increased RSs in this patient. These findings suggest that loss of the ABCB7 gene may be a pathogenetic factor underlying mitochondrial iron accumulation in RARS patients with idicXq13.

Translocation (X;20)(q13.1;q13.3) as a primary chromosomal finding in two patients with myelocytic disorders

Reports of X chromosome translocations, as primary chromosomal changes associated with hematologic disorders, remain relatively uncommon. Herein, we report the detection, by conventional cytogenetic methods, of a cytogenetically identical t(X;20) in two different patients with hematologic disorders (probable myelodysplasia and polycythemia vera/acute myelocytic leukemia). In both cases, this translocation appeared as the primary clonal chromosome abnormality, with breakpoints occurring in the long arms of both the X chromosome and chromosome 20 (Xq13.1 and 20q13.3, respectively). Further characterization and comparison of the translocation chromosome products of these two cases by use of fluorescence in situ hybridization techniques is also described. Similar previously reported cytogenetically cases and the potential that this specific rearrangement may represent a nonrandom chromosomal finding are discussed.

Characterization of a highly complex region in Xq13 and mapping of three isodicentric breakpoints associated with preleukemia

The chromosomal abnormality represented by an isodicentric X chromosome [idic(X)(q13)] is associated with a subset of acute myeloid leukemia (AML) and preleukemia observed in elderly females. A previous study localized the breakpoints of two acquired isodicentric X chromosomes associated with myelodysplasia to a 450-kb region proximal to the XIST gene. Here we report the construction and extensive characterization of a reliable 1-Mb P1 artificial chromosome and bacterial artificial chromosome contig covering a highly problematic region in Xq13 that includes the previously described isodicentric breakpoint region. In addition to mapping of the brain-specific gene (NAP1L2) and the phosphoglyceryl kinase alpha subunit 1 gene (PHKA1) and generation and mapping of a large number of STSs throughout the contig, we have mapped a putative transcriptional regulatory protein (HDACL1), and 35 ESTs. Sequencing data, Southern blot analysis, and fiber-FISH analysis have permitted characterization of extensive region-specific duplications and triplications in addition to an unusually high concentration of long interspersed repeat elements, both of which could be implicated in isodicentric chromosome formation and other Xq13 chromosome aberrations. FISH analysis of metaphase chromosomes from two previously unpublished AML patients and one preleukemic patient using cosmid clones and selected subclones allowed mapping of the idic(X)(q13) breakpoints to a 100-kb interval, consistent with the involvement of an X-linked gene in the genesis of this form of preleukemia, disruption of which may represent a preliminary step in progression to AML. Assembly and physical mapping of this complex 1-Mb contig establish a foundation for ongoing sequencing and gene identification projects in the region.

Isodicentric chromosome 21: a novel aberration in acute myeloid leukemia

We present here a 78-year-old female patient with acute myeloid leukemia (AML), French-American-British classification M2, exhibiting isodicentric chromosome 21, idic(21)(q22), at the time of diagnosis. The patient had three idic(21)(q22), besides the del(5)(q13q32), add(21)(q22), dic(21;22) (q22;q13), and +22. Fluorescence in situ hybridization studies with whole-chromosome painting and centromere-specific probes for chromosome 21 verified the diagnosis of idic(21)(q22). There were no distinct clinicohematological characteristics of AML with isodicentric 21. The patient was treated with remission-induction therapy followed by consolidation therapy. Two years later, the patient showed the disappearance of isodicentric 21 but retained del(5)(q13q32) and gained other chromosomal abnormalities, +add(17)(p11) and -16. To our knowledge, this is the first report of AML with acquired idic(21)(q22).

Monosomy X as a recurring sole cytogenetic abnormality associated with myelodysplastic diseases

Solitary loss of the X chromosome is associated with Turner syndrome and not hematological disorders. We describe five patients with non-constitutional loss of the X chromosome as the sole cytogenetic abnormality in their bone marrow. Three of the five patients had myelodysplastic syndrome (MDS), one case had AML M-6 with evidence suggestive of an evolving MDS, and the last patient had a dysplastic marrow. A review of the literature identified sporadic reports of an association of monosomy X and several hematologic disorders, as well as a few solid tumors. In this series of patients, monosomy X as a sole non-constitutional cytogenetic abnormality in bone marrow is associated with myelodysplastic diseases. In addition, fluorescence in situ hybridization analysis with an X centromere probe indicated that monosomy X was present in erythroid precursors, myeloblasts, promyelocytes, myelocytes, metamyelocytes, granulocytes, and monocytes, while mature lymphocytes presented with two copies of the X chromosome. The molecular cytogenetic evidence supports the diagnosis of a myelodysplastic disorder in these cases and documents the potential role of FISH in hematological disease.

Isodicentric (X)(q13) in haematological malignancies: presentation of five new cases, application of fluorescence in situ hybridization (FISH) and review of the literature

Idic(X)(q13) represents a rare but recurrent chromosomal abnormality in haematological malignancies. We present five new cases characterized by this particular aberration and review the literature on this subject. The patients were elderly females with a diagnosis of refractory anaemia (1/5), refractory anaemia with ringed sideroblasts (2/5), chronic myelomonocytic leukaemia (1/5), and Philadelphia chromosome-negative chronic myeloid leukaemia (1/5). Three out of the five patients demonstrated an increased proportion of bone marrow ringed sideroblasts. After a follow-up period of 30-57 months all patients but one are alive. Idic(X)(q13) always occurred as the sole chromosomal abnormality, either in one or in two copies. We confirmed the dicentric nature of the aberration by fluorescence in situ hybridization (FISH) on metaphases as well as interphase nuclei using an X-chromosome-specific alpha-satellite probe, and performed chromosome painting to visualize possible additional chromosomal changes involving the X chromosomes. Our findings and the data of 17 previously published cases indicate that idic(X)(q13): (1) may play a significant pathogenetic role in haematological malignancies affecting exclusively females and deriving predominantly from early progenitor cells; (2) is frequently associated with a pathological iron accumulation; (3) indicates a variable prognosis.

Characterization by chromosome painting of balanced and unbalanced X chromosome translocations in myelodysplastic syndromes

Structural anomalies of the X chromosome, especially translocations, are rare events in myelodysplastic syndromes (MDS). In a series of 2270 MDS patients analyzed between 1983 and 1994 (Center for Human Genetics, Leuven), 9 cases were found with translocations involving the X chromosome. These aberrations were not restricted to specific FAB subtypes and were the sole anomalies in 3 cases. In the remaining 6 patients, they were associated with other abnormalities, including 5q-, observed in three cases. Fluorescence in situ hybridization (FISH) was retrospectively performed on 8 patients and was shown to be a useful complement for the characterization of the translocations involving the X chromosome. In 3 cases, we could identify translocation partners and breakpoint regions only by using chromosome painting. No recurrent chromosome partners were observed. The breakpoints could be localized along the whole X chromosome. There was, however, a cluster in the Xq13 region involved in 4 of the 9 patients. The previously reported association of Xq13 anomalies with refractory anemia with ringed sideroblasts (RARS) was found in only one case. Despite the lack of characteristic translocations involving the X chromosome, the occurrence of such changes as the sole karyotypic anomaly suggests that they could play a role in the pathogenesis of some myelodysplastic syndromes.

Cytogenetic and FISH studies of abnormal X chromosomes in a patient with ANLL

We report a case of idic(X)(q13),r(X)(p22q13), and del(X)(:p11-->cen-->q11:) in a 71-year-old female patient with de novo acute nonlymphocytic leukemia (ANLL), FAB-M4. The abnormal X chromosomes of this patient were identified cytogenetically by G-banding technique and were further confirmed by fluorescence in situ hybridization (FISH) using an alpha-satellite probe to chromosome X centromere. The features of this are compared with other cases reported in the literature.

Twenty-six patients with hematologic disorders and X chromosome abnormalities. Frequent idic(X)(q13) chromosomes and Xq13 anomalies associated with pathologic ringed sideroblasts

In our experience, acquired structurally abnormal X chromosomes are found in about 1% of patients with hematologic disorders who have a chromosomally abnormal clone. Over a 10-year period, we identified 26 patients with hematologic disorders who had an acquired X chromosome abnormality. In 13 of these patients, the breakpoints were at Xq13, and in 13 the had idic(X)(q13) chromosomes. The 13 patients with Xq13 breakpoints were all older females, and 12 had pathologic ringed sideroblasts with dysmyelopoietic syndromes or a history of these syndromes. Among the 13 patients with breakpoints other than Xq13, seven were male and six were female; only one of these patients had pathologic ringed sideroblasts, and all of these patients had a variety of hematologic disorders. Xq13 may contain genes that, when altered by the formation of chromosome abnormalities, may be associated with neoplastic disorders involving pathologic ringed sideroblasts.