Cancer Genetics and Cytogenetics 198 (2010) 162e165

Short communication

JAK2 V617F-positive essential thrombocythemia in a patientwith Klinefelter syndrome: a case report

Ho-Young Yhima, Hee Sun Kimd, Ji-Youn Sohna, Min-Ju Songa, Na-Ri Leea,c, Eun-Kee Songa,c,Sam-Im Choib, Chang-Yeol Yima,c, Jae-Yong Kwaka,c,*

aDivision of Hematology/Oncology, Department of Internal Medicine, Chonbuk National University Medical School, San 2-20 Geumam-dong,Jeonju, 561-712 Korea

bDepartment of Laboratory Medicine, Chonbuk National University Medical School, San 2-20 Geumam-dong, Jeonju, 561-712 KoreacAdvanced Research Cancer Center, Chonbuk National University Medical School, San 2-20 Geumam-dong, Jeonju, 561-712 Korea

dDepartment of Nursing, Jeonbuk Science College, 9-28 Sigi3-dong, Jeongeup, 580-712 Korea

Received 13 November 2009; received in revised form 3 January 2010; accepted 3 January 2010

Abstract Klinefelter syndrome (KS) is the most commo

* Corresponding a

E-mail address: j

0165-4608/10/$ e see

doi:10.1016/j.cancerg

nly diagnosed X chromosome aneuploid syndromeamong males. The association between hematologic malignancies such as non-Hodgkin lymphomaand leukemia and KS has been established recently on the basis of numerous case reports and a largecohort study. The risk of chronic myeloproliferative disease (MPD) as a hematologic malignancy inKS, however, has not been evaluated to date. Moreover, to our knowledge, there is only one case reportthat observed MPD in a patient with KS. Even though the Janus kinase 2 (JAK2) mutation was consid-ered the primary cause in the pathogenesis of MPD, the mutation status was not described in thatreport. We found JAK2 V617F mutationepositive essential thromobocythemia (ET) in a patient withKS. To the best of our knowledge, this case represents the first case report of JAK2 V617F mutation ina patient with KS. Furthermore, we also suggest the hypothesis that X chromosome aneuploidy asa ‘‘pre-JAK2’’ cytogenetic change may be associated with the development of clonal hematopoiesisand carcinogenesis, because of the finding of higher oncogenic potential of extra X chromosome.In this study, we present the first report of JAK2 V617F-positive ET in a patient with KS, as well asa review of the relevant literature. � 2010 Elsevier Inc. All rights reserved.

1. Introduction

Klinefelter syndrome (KS) is the most common X chro-mosome aneuploid syndrome, which is prevalent in0.1e0.2% males [1,2]. The 47,XXY karyotype is the mostcommon chromosomal pattern in patients with KS (80%),and the others are related with higher-grade aneuploidiesor mosaicism [1]. A recent large UK cohort study of menwith KS revealed that the risk of non-Hodgkin lymphomawas higher among men with KS than among the generalpopulation, and the authors of this cohort study suggesteda modest association between leukemia and KS [2]. Therisk of chronic myeloproliferative disease (MPD) as a hema-tologic malignancy, however, was not analyzed in this UKcohort study [2].

MPD is a clonal disorder that includes polycythemia vera(PV), essential thrombocythemia (ET), and primary myelofi-brosis. A Janus kinase 2 (JAK2) mutation is frequently

uthor. Tel.: þ82-63-250-1791; fax: 82-63-254-1609.

ykwak@chonbuk.ac.kr (J.-Y. Kwak).

front matter � 2010 Elsevier Inc. All rights reserved.

encyto.2010.01.001

observed in patients with MPD and is thought to be theprimary causative lesion in the pathogenesis of MPD [3e6].

To our knowledge, so far there has been only one reportof MPD in a patient with KS [7], but no studies have re-ported a JAK2 V617F mutation in patients with KS.Considering the heterogeneity of MPD and oncogenic roleof the extra X chromosome in other hematologic malignan-cies, it is likely that the presence of an extra X chromosomein KS might be associated with the pathogenesis of thisdisease. Here, we present the first case report of a 43-year-old man with KS who had JAK2 V617F-positive ET,and we provide a review of the relevant literature.

2. Materials and methods

2.1. Case report

A 43-year-old man was admitted to our hospital becauseof thrombocytosis observed during a routine health check-up.An initial complete blood count showed a white cell count

Fig. 1. Detection of the JAK2 V617F mutation by PCR. PCR products of

sizes 543- and 352-bp were amplified from bone marrow aspirates at initial

diagnosis. The 543-bp band represents wild-type JAK2, while the 352-bp

band indicates the presence of the valine-to-phenylalanine mutation at

position 617 in the JH2 domain of JAK2. The patient had, therefore,

a heterozygous JAK2 V617F mutation. PC, positive control; NC, negative

control; Pt, patient.

163H.-Y. Yhim et al. / Cancer Genetics and Cytogenetics 198 (2010) 162e165

of 13,450/mm3 (69.6% neutrophils), hemoglobin of 12.3 g/dL, and a platelet count of 1,110,000/mm3. The patient ap-peared otherwise healthy, and his medical history was unre-markable. Upon examination during admission,hepatosplenomegaly was not evident, but the volume ofeach testis was decreased, and only sparse facial, axillary,and pubic hair was present. He also had a unique tone ofvoice. He had been never married. The laboratory findingsshowed that the patient had a normal level of prolactin(13.6 ng/mL; normal range, 1.8e15.9 mL), but an elevatedserum level of follicle-stimulating hormone of 36.9 (normalrange, 2.4e19 mIU/mL), with a decreased level of total andfree testosterone of 0.3 ng/mL (normal range, 2.36e9.96ng/mL) and 0.8 (normal range, 8.8e27 pg/mL), respec-tively, indicating hypergonadotropic hypogonadism. Toevaluate thrombocytosis, bone marrow aspiration andbiopsy were performed. The bone marrow aspirationshowed a markedly increased number of megakaryocytes,which occasionally formed clusters. Trilineage hematopoi-esis with normal maturation was observed, however, andthe estimated cellularity of the bone marrow section wasabout 30e40%. JAK2 mutation analysis based on poly-merase chain reaction (PCR) amplification of achievedmarrow aspirates was performed with a Seeplex JAK2ACE Genotyping kit (Seegene, Seoul, Korea), which is de-signed to detect the somatic point mutation from valine tophenylalanine at position 617 in the JH2 domain ofJAK2. This analysis revealed that the patient had a heterozy-gous JAK2 V617F mutation (Fig. 1). Furthermore, cytoge-netic studies of the marrow aspirates revealed 15metaphases, all of which were 47,XXY (Fig. 2). The patientwas treated with a combination of hydroxyurea and aspirinwithout any acute or chronic thrombotic complicationsduring a 1-year follow-up period, and the patient’s plateletcount decreased to below 400,000/mm3. He is currently ingood health.

3. Results and Discussion

Several studies have suggested that patients with consti-tutional chromosomal abnormalities may be more suscep-tible to malignancy. For example, children with trisomy21 have an 18-fold increased risk of developing acuteleukemia [8], and women with X chromosome monosomyhave an increased risk for central nervous system tumors[9]. KS is the most commonly diagnosed sex chromosomedisorder among males. Similar to other constitutional chro-mosomal abnormalities, men with KS have an increasedrisk of male breast cancer and mediastinal germ cell tumors[10,11]. The largest UK cohort study to date also revealedthat men with KS might have substantially elevated risksfor breast and lung cancer development [2]. Furthermore,this study revealed that the risk of hematologic malignancylike non-Hodgkin lymphoma, as well as solid organ malig-nancies, was increased in KS, and suggested possibility of

a modest association between KS and leukemia [2]. Therisk of MPD in patients with KS could not be evaluatedin this cohort study, however, because hematologic malig-nancies aside from lymphoma and leukemia were notincluded in the analysis. Moreover, considering that only10% of KS patients are diagnosed before or during pubertyand about two thirds of all patients with KS are not diag-nosed during the course of their lives [1,12], the assessmentof disease risk in patients with KS should be interpretedwith caution.

Chronic MPD is a clonal disorder that includes PV, ET,and primary myelofibrosis. In recent studies, the JAK2V617F mutation has been shown to occur at a highfrequency in Philadelphia-negative MPD. JAK2 is a cyto-plasmic tyrosine kinase that instigates intracellularsignaling triggered by hematopoietic growth factors suchas erythropoietin. The valine-to-phenylalanine mutation atamino acid position 617 of JAK2 gene causes cytokine-independent activation of downstream signaling pathways,such as the Janus kinase and signal transducers and activa-tors of transcription (JAK-STAT) pathway, and the phos-phatidylinositol 3-kinase (PI3K) pathway in erythroid andmyeloid cells. As a result, many phenotypic features ofMPD were expressed [3e6].

Although an acquired somatic mutation in the JAK2gene might represent the main causative lesion in MPD,the role of the JAK2 V617F mutation in disease develop-ment would be more complex. The JAK2 mutation in someMPD might be sufficient to induce clonal hematopoiesisand the expression of MPD phenotypes. Some authors,however, have proposed that in some particular entity ofMPD, clonal hematopoiesis might be caused by a mutation

Fig. 2. Karyotyping using a conventional G-banding technique from bone marrow aspirates showing an extra X chromosome in our patient.

164 H.-Y. Yhim et al. / Cancer Genetics and Cytogenetics 198 (2010) 162e165

of as-yet-unknown gene that precedes the JAK2 V617Fmutation [3,13,14]. This advocates the ‘‘multi-hit’’ patho-genesis of MPD, in which mutations that cause clonalhematopoiesis occur before the JAK2 V617F mutation[3,13,14]. Kralovics et al. [13] reported that the percentageof granulocytes and platelets with the JAK2 V617F muta-tion was often markedly lower than the percentage of clonalgranulocytes determined by the X chromosome clonalitymarkers IDS and MPP1. This suggests that some proportionof MPD have the JAK2 V617F mutation in the backgroundof clonal hematopoiesis caused by an as-yet-unknown gene.In light of this model of pathogenesis of MPD, cytogeneticaberrations as ‘‘pre-JAK2’’ mutations have attracted moreinterest. Chromosomal abnormalities were observed inapproximately 30e40% of patients with PV or primarymyelofibrosis, while chromosomal aberrations were foundin 5e10% of patients with ET [14]. Campbell et al. [15]recently reported that some cytogenetic abnormalities, suchas trisomy 9 and deletion of chromosome 20q, were invari-ably observed in JAK2 V617F-positive MPD. Furthermore,Kralovics and colleagues reported a similar discrepancybetween the percentage of granulocytes carrying theJAK2 V617F mutation and deletion of chromosome 20q,an autosomal, X chromosomeeindependent clonalitymarker [13]. Although the relationship between cytogeneticabnormalities and the JAK2 V617F mutation is obscure,cytogenetic aberrations, such as the deletion of chromo-some 20q, may represent the ‘‘pre-JAK2’’ mutation thatcauses clonal hematopoiesis [13]. Thus, these findingssuggest the possibility that some yet-unknown cytogenetic

aberrations may be related with the development of clonalhematopoiesis in some proportion of MPD with JAK2V617F mutation.

The X chromosome is large and contains 1,098 genes,which encode 99 proteins expressed in the testis and invarious tumor types [16]. The X chromosome has manyunique features that differentiates it from autosomes.Females inherit an X chromosome from each parent, butmales only inherit a single X chromosome from theirmothers. Males and females express equal quantities ofproteins encoded by genes on the X chromosome, eventhough females have two X chromosomes. Thus, infemales, gene expression from one of the two X chromo-somes is silenced by a process known as unbalanced Xchromosome inactivation [16]. Although the relationshipbetween the X chromosome and clonal hematopoiesisremains to be elucidated, it has been suggested that X inac-tivation might be partly responsible for clonal hema-topoiesis [2,16e18]. For example, Vassiliou et al. [18]reported a case of ET harboring t(X;5)(q13;q33) involvingthe inactive X chromosome and associated with silencingof autosomal genes within the adjacent 5qe syndromecommon deleted region. Furthermore, some studies havereported that constitutive aneuploidy is related to carcino-genesis due to mutations in yet-unknown genes, which leadto oncogene activation or the loss of function of tumorsuppressor genes [19]. Therefore, it can be hypothesizedthat X chromosome abnormalities, such as translocationand aneuploidy, might be responsible for clonal hema-topoiesis and carcinogenesis through the mechanism of

165H.-Y. Yhim et al. / Cancer Genetics and Cytogenetics 198 (2010) 162e165

autosomal silencing adjacent to an inactive X chromosomeeautosome translocation and overexpression of an oncogeneon the X chromosome that has escaped X inactivation, eventhough direct evidence of association between KS andMPD cannot be given.

We could not exclude the possibility that the observedJAK2 V617F mutation might have been a coincidentalpoint mutation in a patient with KS. Nonetheless, as dis-cussed above, some cytogenetic abnormalities could berelated with clonal hematopoiesis. Moreover, it has beensuggested that X chromosome aneuploidy could be a predis-posing factor for clonal disease as a result of higher onco-genic potential.

In conclusion, we have presented the first case of JAK2V617F-positive ET in a patient with KS. Recent discoveryof the JAK2 V617F mutation has shed light on the patho-genesis of MPD. Additional cytogenetic changes may alsoplay a role in MPD, however, given the heterogeneity in thepathogenesis of MPD. We suggest the hypothesis that thepresence of an extra X chromosome may facilitate thedevelopment of clonal hematopoiesis. To clarify this ambi-guity, further advances in understanding the pathogenesisof this heterogenous entity of disease are required, andlarge epidemiologic studies to determine the nature of theassociation between KS and MPD are also warranted.

Acknowledgments

This study was supported by a grant from the NationalR&D Program for Cancer Control, Ministry of Health &Welfare, Republic of Korea (0620220-1).

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