Isodicentric X chromosome in myeloproliferative disorders

An active isodicentric x chromosome in a case of refractory anaemia with ring sideroblasts associated with marked thrombocytosis

Refractory anaemia with ring sideroblasts and marked thrombocytosis (RARS-T) is a provisional entity in the World Health Organization (WHO) classification. It displays features characteristic of both myelodysplastic syndrome and myeloproliferative neoplasia plus ring sideroblasts ≥15% and marked thrombocytosis. Most patients with RARS-T show a normal karyotype. We report a 76-year-old woman diagnosed with RARS-T (76% of ring sideroblasts) with JAK2 (V617F) mutation and a load of 30-40%. Classical and molecular cytogenetic (FISH) studies of a bone marrow sample revealed the presence of isodicentric X chromosome [(idic(X)(q13)]. Moreover, HUMARA assay showed the idic(X)(q13) as the active X chromosome. This finding was correlated with the cytochemical finding of ring sideroblasts. To our knowledge, this is the first reported case of an active isodicentric X in a woman with RARS-T.

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.