Cancer Genetics and Cytogenetics 158 (2005) 81–83

Short communication

Translocation (X;20) involving the inactive X chromosome in a patientwith myeloproliferative disorder

John O’Reillya,*, Julie Crawforda, Joan Uzaragab, Paul CannellaaDepartment of Haematology, Royal Perth Hospital, GPO Box X2213, Perth, Western Australia 6847

bCytogenetic Department, King Edward Memorial Hospital for Women, Perth, Western Australia

Received 6 July 2004; received in revised form 18 August 2004; accepted 19 August 2004

Abstract We report a patient with an unclassifiable myeloproliferative disorder and the rare t(X;20)(q13;q13.3)as the sole cytogenetic abnormality. The breakpoint on Xq is consistent with other reports oftranslocations involving the X chromosome with breakpoints that cluster to Xq13 and associationwith myeloid disorders. Late replication studies demonstrated the inactive X chromosome wasinvolved in this translocation. The critical event in patients with myeloproliferative disease anddeletion of 20q appears to be the loss of tumor suppressor genes. This may also be the mechanismin this patient with a potential cryptic deletion associated with the translocation. Alternatively,spreading of X inactivation into the derivative chromosome 20 provides a second mechanism forthe loss of function of tumor suppressor genes on 20q. The finding in this patient of t(X;20)together with three others reported in the literature indicates that this may represent a primary non-random abnormality associated with myeloid malignancy, which may take on clinical significancewith the accumulation of more cases. � 2005 Elsevier Inc. All rights reserved.

1. Introduction

Translocations involving the long arm of chromosome Xhave infrequently been reported in the literature. One studyfound the incidence of translocations involving the X chromo-some to be 0.4% in myelodysplastic syndrome (MDS) [1]and a second study found a structurally abnormal X chromo-some in 1% of abnormal hematological samples [2]. In bothstudies, the breakpoint on the X chromosome clustered toXq13 in 50% of cases with a strong association to MDS [1,2].

Translocation (X;20) has previously been described as aprimary abnormality in only 3 patients with myeloid disorders[1,3]. We report a fourth case of an apparent primaryt(X;20)(q13;q13.3). This occurred as a single abnormality ina patient with a myeloproliferative disorder (MPD).

Deletion of the long arm of chromosome 20 is a commonnonrandom finding in patients with MPD, MDS, and acutemyeloid leukemia (AML) [4–6].

In this patient, X inactivation studies offer an alternatemechanism to deletion for the loss of function of tumorsuppressor genes on 20q.

* Corresponding author. Tel.: �61-8-92248742; fax: �61-8-92243449.E-mail address: john.oreilly@health.wa.gov.au (J. O’Reilly).

0165-4608/05/$ – see front matter � 2005 Elsevier Inc. All rights reserved.doi:10.1016/j.cancergencyto.2004.08.029

2. Case history

A 64 year-old woman presented to our hospital with a six-month history of generalized fatigue, exertional dyspnea,and easy skin bruising. Past medical history was of a 10 mm,grade 1, estrogen-receptor positive, T1N0M0 infiltratingductal breast carcinoma diagnosed in September 1998. Thiswas managed with breast-conserving surgery followed by acourse of adjuvant radiotherapy. No hormonal therapies orsystemic chemotherapy were administered.

Physical examination revealed a pale lady with no organ-omegaly, lymphadenopathy or focus of infection. Spleno-megaly was notably absent.

The full blood picture was leucoerythroblastic with amacrocytic anemia (hemoglobin 57 g/L, MCV 107 fl, he-matocrit 0.17), marked leucocytosis (WBC 105.9 × 109/L)and moderate thrombocytopenia (platelets 88 × 109/L). Thewhite cell differential showed neutrophils/ band forms 77%,immature myeloid forms 18%, and lymphocytes 5% withno basophilia or eosinophilia.

The bone marrow aspirate was grossly hypercellular witha reduction in erythropoiesis and expanded granulocyticactivity. The majority of granulocytic forms were matureneutrophils with lesser proportions of myelocytes and meta-myelocytes. No increases in myeloid blasts or promyelocyteswere seen. Dysgranulopoiesis and dyserythropoiesis were

J. O’Reilly et al. / Cancer Genetics and Cytogenetics 158 (2005) 81–8382

not evident and micromegakaryocytes were not present.The diagnosis reached was MPD, unclassifiable. The pa-tient was commenced on hydroxyurea therapy. She had arapid response with normalization of the peripheral bloodleukocytosis. The leukocyte count and differential remainsnormal. Moderate thrombocytopenia and mild anemia con-tinue to be present.

3. Material and methods

Cytogenetic studies were performed on bone marrow cellsusing 24-hour unstimulated, synchronized cultures in RPMImedium supplemented with 20% fetal bovine serum. Stan-dard harvesting, banding and staining techniques were usedto produce G-banded metaphase preparations for the detec-tion of chromosomal abnormalities which were describedaccording to the ISCN 1995 [7].

Fluorescence in situ hybridization (FISH) was performedusing the D20S108 (20q12) probe (Vysis, Downers Grove,IL) and standard techniques to score signals on metaphasecells.

Late replication studies were performed using a terminalpulse of 5-bromodeoxyuridine. After staining with Hoechst33258 the preparations were exposed to photolysis andstained with Giemsa.

4. Results

Cytogenetic analysis demonstrated a mosaic karyotypewith eleven out of 20 metaphase cells containing thet(X;20)(q13;q13.3) (Fig. 1). The other 9 metaphase cellsanalyzed had an apparently normal female karyotype,46,XX.

FISH analysis demonstrated a D20S108 signal on thenormal 20q and on the der(20)t(X;20). The translocatedsegment of the X chromosome on the der(20)t(X;20)stained pale with Giemsa after late replication analysis iden-tifying this as the late replicating or inactive X segment(Fig. 2).

5. Discussion

This paper presents a rare cytogenetic abnormality in apatient with MPD. Translocations involving the X chromo-some cluster around q13 and are invariably of myeloid origin[2] suggesting a neoplastic role for the genes in this region.

Though translocations involving the long arm of chromo-some 20 are uncommon [3], deletions on 20q represent oneof the most frequent chromosomal abnormalities seen inMPD [4]. The deletions are generally interstitial [8] andconstitute the major mechanism for loss of heterozygosity on20q in polycythemia vera [9]. Subsequently, a commonlydeleted region (CDR) was established using FISH probes

Fig. 1. G-banded karyotype showing the t(X;20)(q13;q13.3) (arrows).

J. O’Reilly et al. / Cancer Genetics and Cytogenetics 158 (2005) 81–83 83

Fig. 2. Late replication studies showing the pale staining, inactive X (arrow)involved in the translocation.

[10]. Bench et al. redefined a MPD CDR of 2.7 Mb and aMDS/AML CDR of 2.6 Mb with a combined myeloid CDRof 1.7 Mb [11]. The CDR was further narrowed to an approxi-mately 250 kb gene rich region by PAC clone mapping ofdeleted regions associated with 20q rearrangements. Withinthis region, 2 candidate myeloid tumor suppressor genes,PKIG and KRS2, were identified [12].

Due to the large deletions of 20q, however, seen in manycases of myeloid malignancies and the biological and clinicaldifferences between MPD, MDS, and AML it is likely thatmultiple genes are involved. The association of 20q deletionswith reciprocal translocations involving 20q has also beendescribed in 2 cases of t(20;21)(q11;q11) associated withAML and MDS [13].

Folding of the proximal long arm of the X chromosome, amarker for X inactivation [14], was seen in the derivative20 chromosome containing the translocated Xq in this pa-tient. This was also observed in a patient with MPD andt(X;19)(q12;q13.3) [15] and is opposite to the X-inactivationpattern seen in constitutional X:autosome translocations.The inactive X chromosome’s involvement in the transloca-tion was confirmed by X inactivation studies in our patient.

Spreading of X inactivation into the autosomal 20q regionprovides an alternate mechanism to chromosomal deletion forthe loss of function of tumor suppressor genes at this location.

A recent publication described t(X;20)(q13.1;q13.3) in 2patients with hematological malignancies [3]. In this report,it was demonstrated that the X inactivation-specific tran-script gene was relocated to the derivative 20 chromosomein both cases, giving potential for the inactivation of theadjacent 20q.

The finding of t(X;20) in this patient together with 3others reported in the literature lends support to this beinga rare, primary non-random abnormality associated withmyeloid malignancy and specific molecular events involvedin tumorigenesis.

Acknowledgment

This work was supported by the Western Australian AdultLeukaemia Foundation.

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