The JAK2 V617F mutation frequently occurs in patients

Journal of Thrombosis and Haemostasis, 5: 55–61
ORIGINAL ARTICLE
The JAK2 V617F mutation frequently occurs in patients with
portal and mesenteric venous thrombosis
D. COLAIZZO,* L. AMITRANO, G. L. TISCIA,* G. SCENNA,à E. GRANDONE,*
M . A . G U A R D A S C I O N E , V . B R A N C A C C I O à and M . M A R G A G L I O N E § *
*UnitaÕ di Aterosclerosi e Trombosi, IRCCS ÔÔCasa Sollievo della Soerenza‘‘, S. Giovanni Rotondo; Divisione di Gastroenterologia, Ospedale ÔÔA.
CardarelliÕÕ, Napoli; àDivisione di Ematologia, Unità di Coagulazione; and §Genetica Medica, Università di Foggia, Foggia, Italy
To cite this article: Colaizzo D, Amitrano L, Tiscia GL, Scenna G, Grandone E, Guardascione MA, Brancaccio V, Margaglione M. The JAK2 V617F
mutation frequently occurs in patients with portal and mesenteric venous thrombosis. J Thromb Haemost 2007; 5: 55–61.
Summary. Background: Myeloproliferative disorders (MPDs)
represent a risk factor for thrombosis in the portal, mesenteric,
and hepatic districts. Objective: We aimed to assess whether the
Janus kinase 2 (JAK2) V617F mutation, an acquired mutation
that occurs in MPD patients, is a risk factor for portal and
mesenteric venous thrombosis (PMVT) independently of the
presence of overt MPDs. Patients and methods: The medical
histories of 99 patients presenting with PMVT were obtained.
The presence of the JAK2 V617F and VHL 598C > T
mutations was determined by polymerase chain reaction
followed by restriction enzyme analysis and direct cycle
sequence analysis. Results: Over a 10-year period of observation, of the 99 patients presenting with PMVT, the JAK2 V617F
mutation was detected in heterozygous state in 17 individuals
[17.2%; 95% confidence interval (95% CI) 10.9–25.9]. None of
the patients presenting with the JAK2 V617F mutation carried
an inherited thrombophilic risk factor. Seven patients with
(43.8%; 95% CI 19.8–70.1) and two without (2.4%; 95% CI
0.3–8.4) the JAK2 V617F mutation had a diagnosis of MPD at
the occurrence of the venous thrombotic event. After a median
follow-up of 41 months (range 3–114 months), three out of the
10 patients carrying the JAK2 V617F mutation were then
diagnosed as having idiopathic myelofibrosis (n ¼ 2) or
polycythemia vera (n ¼ 1), whereas in seven patients a MPD
was not detected. Two of the 83 patients without the JAK2
V617F mutation went on to develop MPDs. Conclusions:
Determination of the JAK2 V617F mutation may contribute to
the search for genetic determinants of PMVT and may be useful
to recognize patients who should be carefully observed for the
subsequent development of overt MPDs.
Correspondence: Maurizio Margaglione, Cattedra di Genetica
Medica, Dipartimento di Scienze Biomediche, Università degli Studi
di Foggia, viale Pinto, Foggia 71100, Italy.
Tel.: +39 0881 736082; fax: +39 0881 733842; e-mail:
m.margaglione@unifg.it
Received 29 August 2006, accepted 7 October 2006
2006 International Society on Thrombosis and Haemostasis
Keywords: JAK2, mutation, myeloproliferative disorders, risk
factor, venous thrombosis.
Introduction
Venous thrombosis is the third most common cardiovascular
affliction after ischemic heart disease and stroke [1]. The
pathogenesis of venous thrombosis is multifactorial, involving
acquired and genetic factors. In addition to circumstantial
predisposing factors (e.g. surgery, pregnancy, immobilization,
malignancy), genetic predisposition because of molecular
abnormalities of components of the coagulation pathway have
been found in subjects who had suffered from thromboembolic
disease [2]. Splanchnic venous thrombosis, including thrombosis of the hepatic veins or portal venous system, is anuncommon event and may be caused by a variety of conditions
including cirrhosis and cancer, and abdominal infectious and
inflammatory processes [3]. Coexistence of causative factors
was observed in a large setting of patients, indicating that
thrombosis of the portal vein, like other manifestations of
thrombosis, can be a result of combined pathogenetic mechanisms.
Myeloproliferative disorders (MPDs), whether overt or
latent, represent a main intrinsic factor for the development
of thrombosis in the portal, mesenteric, and hepatic areas [4–7].
Venous thrombosis can involve all territories but MPDs,
mainly polycythemia vera (PV) and essential thrombocythemia
(ET), are the commonest underlying etiology for Budd–Chiari
syndrome and PMVT; spontaneous endogenous erythroidcolony formation being seen in up to 78% of patients thought
to have Budd–Chiari Syndrome and in 48% of patients with
splanchnic venous thrombosis [8]. On the other hand, venous
thromboses significantly affect morbidity and mortality of
patients with MPD and are associated with severe organ
damage and high mortality [9].
Recently, several groups identified a recurrent activating
tyrosine kinase mutation, Val617Phe, in the JH2 pseudo-kinase
domain of the Janus kinase 2 (JAK2) gene in patients with
sporadic MPDs. This mutation was found in most patients
with PV and in about half of the patients with ET or
56 D. Colaizzo et al
myelofibrosis (MF) [10–14]. This JAK2 mutation is an
acquired somatic event in sporadic MPDs, leading to a
constitutive activation of the JAK–signal transducer and
activator of transcription signal transduction pathway [15].
It is well-known that PMVT may be an early or presenting
complication of an undiagnosed MPD, particularly in young
patients [4,8] and that a portion of these patients do not fulfill
the diagnostic criteria for MPD but have features suggestive of
a latent form based on hyperplastic bone marrow and erythroid
progenitor cell culture; these cases may subsequently develop
overt MPD. Actually, a meta-analysis of 120 patients from
seven studies indicated that the estimated incidence of underlying MPD depends on the diagnostic criteria used [8]. Very
recently, the JAK2 V617F mutation has been found to occur in
a high proportion of patients with Budd–Chiari syndrome, a
heterogeneous group of disorders resulting from obstruction to
hepatic venous outflow [16].
The Chuvash polycythemia is associated with specific
germline mutations in the von Hippel–Lindau tumor suppressor (VHL) gene, mainly the 598C > T, [17] and is characterized by a higher occurrence of splanchnic venous thrombosis
[18,19].
Thus, we have investigated whether the clonal JAK2 V617F
mutation and/or the VHL 598C > T mutation occur in a high
proportion of non-cirrhotic patients with portal and mesenteric
venous thrombosis (PMVT) and whether determination of
these mutations would be useful in the characterization of
latent MPD in this patient setting.
of employees of the ÔCasa Sollievo della SofferenzaÕ Hospital, S.
Giovanni Rotondo, without a history of venous thromboembolism, served as controls. All subjects who reported a personal
history of clinical venous thrombosis were excluded from the
study. Both cases and controls were Caucasian and were from
the same region. The two groups were comparable for sex,
social status, and age.
After approval from the local Ethics Committees, the study
was carried out according to the Principles of the Declaration
of Helsinki. Informed consent was obtained from all the
subjects.
Blood collection and coagulation tests
Blood samples were collected into vacuum plastic tubes
containing 3.8% trisodium citrate and centrifuged at
2000 · g for 15 min to obtain platelet-poor plasma. After
having filtered a portion for the assessment of lupus anticoagulant, samples were frozen and stored in small aliquots at
)70 C until tested. Antiphospholipid antibodies [lupus anticoagulant and immunoglobulin G anticardiolipin antibodies
(ELISA, Byk Gulden, Italy)], antithrombin, protein C, amidolytic and immunological (Behring, Marburg, Germany) and
total and free protein S antigen (ELISA, Diagnostica Stago,
Asnières, France) were determined in all patients, as reported
elsewhere [21]. Clotting assays were performed on a KC4
Amelung coagulometer (Amelung, Germany). Inter- and intraassay coefficients of all the variables never exceeded 8.0% and
5.0%, respectively.
Materials and methods
DNA extraction and analysis
Patients and controls
Patients with PMVT consecutively diagnosed and followed-up
at Gastroenterology Unit of the ÔA. CardarelliÕ Hospital,
Naples were referred to the Thrombosis Centre of the same
hospital for a work-up at least 3 months after the thrombotic
episode. All subjects with liver cirrhosis, hepatocellular carcinoma, or who reported a personal history of Budd–Chiari
syndrome, were excluded from the study. Between January
1997 and June 2006, we investigated 112 non-anticoagulated
patients (median age 42 years; range 10–85 years), 50 men and
62 women, with a documented portal and/or mesenteric venous
thrombosis. A complete clinical summary, with emphasis on
personal and family history of thromboembolic disease and
circumstantial vascular risk factors (surgery, immobilization,
pregnancy, post-partum, trauma, oral contraception, varicose
veins and malignancy), was obtained from all subjects by a
specially trained staff. Portal and mesenteric venous thromboses were diagnosed by Doppler ultrasonography, spiral computed tomography, or magnetic resonance imaging as required
during the routine diagnostic work-up. MPDs were diagnosed
according to established criteria [20].
Two-hundred and thirty apparently healthy subjects (98 men
and 132 women; median age 44 years; range 21–73 years)
randomly selected from a southern Italian general population
DNA was extracted from peripheral blood leukocytes according to standard protocols [22]. A 220-bp DNA fragment of the
factor (F) V gene that includes the nucleotide 1691 was
amplified and digested with MnlI as previously described [23].
To identify the G > A mutation of the prothrombin gene, a
345-bp fragment was obtained and then digested using the
HindIII endonuclease, as reported [24].
Amplifications of regions of JAK2 gene containing the
V617F were performed as previously described [25]. Genomic
DNA was amplified by polymerase chain reaction (PCR), and
successful amplification was confirmed by electrophoresis on
an ethidium bromide-impregnated 2.0% agarose gel. Oligonucleotide custom synthesis service was from Life Technologies
(Paisley, UK). PCRs were carried out on 50 lL volume
samples, in a Perkin Elmer Cetus thermal cycler (Perkin Elmer
Cetus, Norwalk, CT, USA). Each sample contained 0.1 lg of
genomic DNA, and 20 pmol L)1 each of sense and antisense
primers (5¢-AGCAAGCTTTCTCACAAGCA-3¢ and 5¢CTGACACCTAGCTGTGATCCTG-3¢,
respectively),
125 lM of dNTP, 5 mM Tris–HCl pH 8.3, 50 mM KCl,
1.5 mM MgCl2, and 1 U Taq polymerase. The solution was
overlaid with 50 lL of mineral oil and, after an initial
denaturation step (3 min at 95 C), it was put through 30
cycles, each consisting of 1 min at 95 C, 1 min at 56–60 C
2006 International Society on Thrombosis and Haemostasis
JAK2 V617F mutation and occurrence of PMVT 57
and 2 min at 72 C. Then, 5 lL volumes of the amplification
product were separated in a 2% agarose-gel electrophoresis in
TAE buffer (40 mM Tris-acetate, 1 mM EDTA, pH 7.7)
containing 0.5 lg mL)1 ethidium bromide, and visualized
under ultraviolet light. Amplification products were subjected
to restriction enzyme analysis using 2 IU of the BsaXI
endonuclease (New England Biolabs Inc., Beverly, MA,
USA), as previously reported [25]. The G-to-T transversion
in exon 12 leads to the missing of a site of digestion of BsaXI,
giving rise to an uncut product instead of the two expected
restriction fragments (96 and 56 bp). Then, amplified DNA
fragments showing an abnormal pattern of digestion were
cleaned with a QIAquick PCR purification kit (Qiagen,
Valencia, CA, USA) and subjected to direct cycle sequence
analysis using the Taq dye-deoxy terminator method, the same
primers used for amplification, and an ABI PRISM 310
Genetic Analyzer sequencer (PE Biosystems, Foster City, CA,
USA). Because the JAK2 V617F mutation is an acquired
somatic event, we indirectly assessed the sensitivity of methods
employed to detect it using serial dilutions of the amplification
product from a patient homozygous for the FV Q506 allele
with that from a subject homozygous for the FV R506 allele.
Using the restriction enzyme analysis, we were able to detect
dilutions as low as 5%, whereas the lower limit of the direct
cycle sequence analysis was 20%.
The genotyping of the VHL 598C > T mutation was
performed as previously described [17]. The VHL 598C > T
mutation was identified by Fnu4HI restriction endonuclease
(New England Biolabs) that digests the nucleotide sequence of
the wild allele (C), but its targeted restriction site is abolished by
the C-to-T transition. Then, amplified DNA fragments showing
an abnormal pattern of digestion were cleaned with QIAquick
PCR purification kit (Qiagen) and subjected to direct cycle
sequence analysis using the Taq dye-deoxy terminator method,
the same primers used for amplification, and an ABI PRISM
310 Genetic Analyzer sequencer (PE Biosystems).
Results
Description of the cohort
Between January 1997 and June 2006, 112 patients (50 men and
62 women) were diagnosed with documented PMVT. Thirteen
patients (11.6%) were not studied: consent was refused in one;
DNA samples were not available in four; six were lost in the
follow-up; and there were technical problems in two. Thus, we
analyzed 99 patients (44 men and 55 women; median age
41 years; range 10–85 years).
Demographic characteristics and the incidence of circumstantial and thrombophilic risk factors both in patients and in
controls are shown in Table 1. An acquired thrombophilic risk
factor was identified in 38 (38.4%; 95% CI 28.8–48.7) patients.
The most represented were: history of a hematological
malignancy (n ¼ 11: MPD in nine and lymphoma in two);
previous surgical intervention (n ¼ 10); and the prescription of
oral contraceptives (n ¼ 8). In five patients a moderate
hyperhomocysteinemia was found, and no patient displayed
antiphospholipid antibodies.
Patients had a higher incidence of the FII A20210 but not of
the FV Leiden mutation. Actually, in this setting, the number
of carriers of the FV Leiden mutation was eight (8.1%; 95% CI
3.6–15.3), seven heterozygotes and one homozygote, among
patients, and nine heterozygotes (3.9%; 95% CI 1.8–7.3; OR
2.2; 95% CI 0.8–5.6) in healthy individuals. The FII A20210
mutation was detected in 12 cases (12.1%; 95% CI 6.4–20.2),
all heterozygotes, and, in the heterozygous state, only in seven
controls (3.0%; 95% CI 1.2–6.2; OR 4.4; 95% CI 1.7–11.2).
Frequencies of all the mutations were similar in men and
women (not shown). One patient was homozygous for the FV
Leiden mutation and heterozygous for the FII A20210 mutation.
In seven patients the coexistence of acquired and inherited
Table 1 Clinical characteristics and thrombophilic risk factors in controls
and patients investigated
Statistical analysis
All analyses were performed according using SPSS version 11.0
(SPSS Inc., Chicago, IL, USA). The significance of any
difference in means was evaluated by non-parametric test,
whereas the significance of any difference in proportions was
tested by chi-squared statistics. The allele frequencies were
estimated by gene counting, and genotypes were scored. The
observed numbers of each gene mutation [Factor V Leiden (FV
Leiden), FII A20210, JAK2 V617F, and VHL 598C > T] were
compared with those expected for a population in Hardy–
Weinberg equilibrium using a chi-squared test. The significance
of the difference of observed alleles and genotypes between the
groups was tested using the chi-squared analysis after grouping
homozygous and heterozygous carriers of the FV Leiden
mutation. Odds ratio (ORs) and 95% confidence intervals
(95% CIs) were calculated. 95% CIs of a proportion were
calculated using the modified Wald or exact method as
required. Statistical significance was taken as P < 0.05.
2006 International Society on Thrombosis and Haemostasis
Variables
Controls
Patients
Age (years), median (range)
Men, n (%)
Acquired risk factors, n (%)
Hematologic malignancy, n (%)
Surgery, n (%)
Oral contraceptives, n (%)
Homocysteine > 95 centile, n (%)
Others, n (%)
Inherited risk factors, n (%)
Factor V Leiden, n (%)
Factor II A20210 allele, n (%)
Antithrombin deficiency, n (%)
Protein C deficiency, n (%)
Protein S deficiency, n (%)
Risk factors, n (%)
Combined risk factors, n (%)
44.0 (21–73)
98 (42.6%)
NA
NA
NA
NA
NA
NA
NA
9 (3.9)
7 (3.0)
NA
NA
NA
NA
NA
41.0
44
38
11
10
8
5
8
21
8
12
0
2
0
53
12
(10–85)
(44.4%)
(38.4%)*
(11.1%)
(10.1%)
(8.1%)
(5.1%)
(8.2%)
(21.2%) (8.1)à
(12.1)§
(2.0)
(53.5%)
(12.1%)
*Four patients carried combined acquired risk factors; one patient
carried combined inherited risk factors. àOR 2.2; 95% CI 0.8–5.6;§ OR
4.4; 95% CI 1.7–11.2. NA, not applicable.
58 D. Colaizzo et al
thrombophilic risk factors was observed. Two additional
patients had an isolated protein C deficiency. As a whole, a
thrombophilic risk factor was identified in 53 patients (53.5%;
95% CI 43.2–63.6) and in 12 of them (12.1%; 95% CI 6.4–
20.2) more than one risk factor was recorded. The median age
of patients carrying a thrombophilic risk factor was 42 years
(range 15–80 years) and was similar to that of patients without
thrombophilic risk factors (40.0 years; range 10–72 years)
(P ¼ 0.612; Mann–Whitney U-test).
JAK2 V617F mutation and the occurrence of PMVT
Among patients with PMVT, 17 (17.2%; 95% CI 10.9–25.9),
five men and 12 women, carried the JAK2 V617F mutation
(Table 2); all were heterozygotes. No members of the control
group were found to carry the mutant allele. Samples from all
subjects with PMVT and carrying the JAK2 V617F mutation
were sequenced. In 16 out of 17 patients, the sequencing
analysis showed a concordance with results obtained with the
restriction fragment length analysis. In these patients, allele
quantization, estimated taking into account the relative area of
both alleles, gave comparable results for the wild (G) and the
mutant (T) allele, the ratio never exceeding 60%. In the
remaining patient, a 28-year-old woman, the mutant allele was
detected only by restriction enzyme analysis. The median age of
positive patients was 44 years (range 28–85 years) and was
slightly higher than that (39.5 years; range 10–72 years) of the
82 (82.8%; 95% CI 74.1–89.1) patients, 39 men and 43 women,
without the JAK2 V617F mutation (0.195; Mann–Whitney Utest). None of patients presenting with the JAK2 V617F
mutation carried an inherited thrombophilic risk factor, such
as FV Leiden, FII A20210 mutation, or protein C deficiency.
The knowledge of a MPD at the occurrence of the venous
thrombotic event was recorded in seven (41.2%; 95% CI 18.4–
67.1) patients with and two (2.4%; 95% CI 0.3–8.5) without the
JAK2 V617F mutation. As a whole, acquired thrombophilic
risk factors were recorded in 11 patients (64.7%; 95% CI 41.2–
82.8) carrying the JAK2 V617F mutation and in 25 (30.5%;
95% CI 21.6–41.2) without (P ¼ 0.012; two-tailed Fisher’s
exact text). However, after excluding MPD, the difference was
no longer significant, other acquired risk factors being found in
only four patients (Table 2). Overall, the JAK2 V617F
mutation was detected in seven out of nine patients (77.8%;
95% CI 40.0–97.2) presenting with a known MPD, as shown
by peripheral blood counts and bone marrow biopsy. In detail,
three patients with idiopathic MF, two out of three with ET,
one out of two with PV, and one woman with chronic myeloid
leukemia showed the JAK2 V617F mutation.
VHL 598 C > T mutation and the occurrence of PMVT
Among patients with PMVT, two (2.0%; 95% CI 0.3–7.1), a
38-year-old man and a 28-year old woman, carried the VHL
598C > T mutation; both were heterozygotes. The presence of
the mutation in a heterozygous condition was confirmed by
sequencing analysis. No members of the control group were
found to carry the mutant allele (P ¼ 0.180; two-tailed Fisher’s
exact test). None of patients presenting with the VHL
598C > T mutation carried an acquired thrombophilic risk
factor, whereas the FII A20210 mutation was identified in the
male patient.
Follow-up of patients presenting with PMVT
All patients presenting with PMVT without a known diagnosis
of MPD had serial evaluations of hematocrit and hemoglobin,
and leukocyte and platelet counts. In addition, a karyotype
analysis and the search for the bcr-abl rearrangement was
performed in all subjects. During the follow-up (median
41 months; range 3–114 months), five out of 90 patients
(5.6%; 95% CI 1.8–12.5) went on to develop MPDs: two
idiopathic MF (one man and one woman), one PV (woman),
Table 2 Clinical characteristics of patients carrying the JAK2 V617F mutation
Patient
Sex
Age at diagnosis
Year
Myeloproliferative disorders
Risk factors
Vein thromboses
SMP
VC
CMR
CA
DSMR
LR
SM
GR
LR
TA
CA
NC
MM
LF
DM
NA
LA
Woman
Woman
Woman
Woman
Woman
Woman
Woman
Woman
Man
Man
Man
Man
Woman
Woman
Man
Woman
Woman
49
61
52
44
46
35
80
52
50
42
85
42
28
34
80
36
38
1997
1997
1998
2000
2000
2000
2000
2001
2001
2002
2003
2003
2003
2004
2006
2006
2006
PV during the work-up
CML known
ET known
MF during follow-up
No
MF known
MF known
No
MF during follow-up
ET known
No
PV known
No
No
No
MF known
No
None
Hypehomocysteinemia
None
Abdominal surgery
None
None
None
Nnone
None
None
Hyperhomocysteinemia
None
None
Oral contraceptives
None
None
None
Portal, mesenteric
Spleen, portal, mesenteric
Portal, mesenteric
Portal, mesenteric
Portal
Portal, mesenteric
Portal
Portal, mesenteric
Portal, mesenteric
Portal
Portal
Portal, mesenteric
Spleen, portal
Spleen, portal, mesenteric
Spleen, portal, mesenteric
Portal, mesenteric
Portal
CML, chronic myeloid leukemia; ET, essential thrombocythemia; MF, idiopathic myelofibrosis; PV, polycythemia vera.
2006 International Society on Thrombosis and Haemostasis
JAK2 V617F mutation and occurrence of PMVT 59
and two ET (two women). Among the 10 patients (three men
and seven women) carrying the JAK2 V617F mutation and
presenting with PMVT without a diagnosis of MPD, three (one
man and two women) were then diagnosed as having MF (n ¼
2) or PV (n ¼ 1). Thus, in seven patients (two men and five
women) a MPD was not detected (Fig. 1). In fact, complete
blood counts taken during the follow-up showed hematocrit,
hemoglobin, and leukocyte and platelet counts that did not
exceed 45%, 145 g L)1, 8.0 · 109 L)1, and 500 · 109 L)1,
respectively. A bone marrow biopsy was carried out in two
women (patients DSMR and GR) and no sign of hyperplasia
or fibrosis was found.
Discussion
Splanchnic venous thrombosis is increasingly recognized as a
multifactorial disorder, although the specific combination of
genetic and acquired risk factors or local precipitating events
may differ between patients. Risk factors include genetic,
acquired systemic factors and local precipitating factors in the
portal/hepatic area. Local factors comprise disorders leading to
decreased portal flow, such as liver cirrhosis and hepatobiliary
malignancies [26,27]. Of the hereditary factors, deficiencies of
the natural anticoagulant proteins, protein C, protein S and
antithrombin, FV Leiden and FII G20210A mutation have
been reported as risk factors for venous thrombosis both in the
presence and the absence of cirrhosis [3,28,29]. In the present
study, we confirm that in patients presenting with PMVT but
without local precipitating factors, such as liver cirrhosis and
hepatobiliary malignancies, inherited thrombophilic risk factors significantly contribute to the multifactorial etiology of
venous thrombosis, being present in 21 patients (21.2%).
Systemic, acquired risk factors include uncommon disorders
associated with a high relative risk of PMVT (MPD,
antiphospholipid syndrome and paroxysmal nocturnal hemoglobinuria), as well as more common factors, such as cancer,
inflammation, oral contraceptives/hormone replacement therapy, pregnancy and postpartum, etc. As a whole, a thrombophilic risk factor was identified in about one half of patients
(53.5%) presenting with PMVT and the coexistence of
causative factors was observed 12 (12.1%), indicating that
thrombosis of the portal vein system, like other manifestations
of thrombosis, can be a result of combined pathogenetic
mechanisms [3,30].
Chronic MPDs, such as PV and ET, follow a chronic clinical
course with increased risk of thrombosis and of evolution to
MF with myeloid metaplasia or acute leukemia [31,32].
Thrombosis remains the most frequent complication during
follow-up and is the main predictor of death in both PV and
ET.
We have found a high incidence of the JAK2 V617F
mutation in patients with PMVT. Of note, only seven of the 17
JAK2 V617F-positive subjects with PMVT were previously
known to have MPDs. Three other JAK2 V617F-positive
patients had a diagnosis of MPD after the occurrence of
PMVT and therefore represent a group with a Ôlatent formÕ of
MPD. The remaining cases failed to fulfill the accepted
diagnostic criteria for MPDs, which suggests that they should
be carefully observed for the subsequent development of overt
MPDs. MPDs are all associated with clonal hematopoiesis,
with the key abnormality originating within the hemopoietic
stem cell. Whereas clonality in the majority of cases of chronic
myeloid leukemia can be established by Philadelphia chromosome or bcr-abl detection, a clonal cytogenetic abnormality is
found in only a minority of cases of ET, PV, and idiopathic
MF. Although all but one positive sample were confirmed after
the sequencing analysis, none of the patients was homozygous
for the JAK2 V617F mutation in circulating blood cells. These
112 patients with PMVT
13 patients not investigated
99 patients studied for JAK2 V617F
82 negative for
JAK2 V617F
2 + ve for MPD
at the PMVT
2 + ve for MPD
during the follow - up
80 – ve for MPD
at the PMVT
2 – ve for MPD
during the follow - up
17 negative for
JAK2 V617F
7 + ve for MPD
at the PMVT
3 + ve for MPD
during the follow - up
10 – ve for MPD
at the PMVT
7 – ve for MPD
during the follow - up
Fig. 1. Flow diagram of patients investigated showing principal findings according to the JAK2 V617F mutation and the presence of MPD. PMVT, portal
and mesenteric venous thrombosis.
2006 International Society on Thrombosis and Haemostasis
60 D. Colaizzo et al
findings are in agreement with previous data in which
homozygosity for the JAK2 V617F mutation was detected
only in a reduced portion of patients [33]. We have studied total
white blood cells. It is conceivable that the analysis of purified
neutrophils would have detected patients with a very low
percentage of cells carrying the mutant allele [33]. However,
present data support the concept that the presence of JAK2
V617F is not sufficient in itself for the MPD phenotype, the
subsequent occurrence of which is presumably determined by
additional acquired mutations over time in a process of clonal
evolution [34].
Results observed in PV have parallels in Chuvash polycythemia, a unique VHL syndrome characterized by homozygous
germline mutations of VHL gene, mainly VHL 598C > T
homozygotes [17]. In this syndrome, a higher occurrence of
splanchnic venous thrombosis has been reported [18,19],
suggesting that the higher incidence of thrombosis in patients
with PV than in those with ET, together with the finding that
the JAK2 V617F mutation in ET appears to promote a PV
phenotype, may have a common mechanism: a polycythemic
condition with an unusually high tendency for thrombosis via
increased hematocrit. Although Chuvash polycythemia is a rare
condition of erythrocytosis, it is endemic in the southern Italy
[35]. Thus, it is conceivable that homozygosity for VHL
598C > T mutation might be identified as risk factor in
patients with PMVT. We have found only two heterozygotes
and both of them have experienced a PMVT. However, giving
the low number of carriers of the mutant allele, present data
cannot provide useful insights into this issue.
In conclusion, the JAK2 V617F mutation is frequently
found in patients with PMVT and a portion of them do not
suffer from an overt MPD. An understanding of the genetic
factors predisposing to PMVT is important in identifying
subgroup(s) of at-risk patients. Present findings suggest that, in
patients presenting with PMVT, screening for the JAK2 V617F
mutation may be useful to recognize patients who should be
carefully observed for the subsequent development of overt
MPDs.
Disclosure of Conflict of Interests
The authors state that they have no conflict of interest.
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