AbstractBackgroundJ-point elevation has been demonstrated to be associated with ventricular fibrillation (VF) and has been proposed as a cause of the J-wave syndrome (JWS). A mutation of KCNJ8, S422L, was reported as a culprit gene. This study aimed to determine the prevalence of KCNJ8 mutations in a Japanese population with JWS or idiopathic VF (IVF).MethodsA total of 230 probands with JWS and IVF underwent genetic screening of KCNJ8. To analyze and compare clinical and electrocardiographic characteristics, the probands were divided into 4 groups: Brugada (Br) pattern only, early repolarization (ER) pattern only, Br and ER patterns, and true IVF.ResultsThe results of the genetic analysis revealed no S422L or other KCNJ8 mutations and indicated no significant difference between the groups.ConclusionThe KCNJ8 mutation showed no association with JWS or IVF among our Japanese patients

Fukuyama, Megumi

Hayashi, Hideki

Horie, Minoru

Kato, Koichi

Kawamura, Mihoko

Kimura, Hiromi

Makiyama, Takeru

Naiki, Nobu

Ohno, Seiko

Wang, Qi

Elsevier - Publisher Connector 

Journal of Arrhythmia 29 (2013) 261–264Contents lists available at ScienceDirectJournal of Arrhythmia1880-42
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E-mjournal homepage: www.elsevier.com/locate/joaOriginal ArticleGenetic screening of KCNJ8 in Japanese patients with J-wave
syndromes or idiopathic ventricular ﬁbrillation$
Qi Wang, BSca, Seiko Ohno, MD, PhDa, Koichi Kato, MDa, Megumi Fukuyama, MDa,
Takeru Makiyama, MD, PhDb, Hiromi Kimura, MD, PhDa, Nobu Naiki, MDa,
Mihoko Kawamura, MDa, Hideki Hayashi, MD, PhDa, Minoru Horie, MD, PhDa,n
a Department of Cardiovascular and Respiratory Medicine, Shiga University of Medical Science, Otsu 520-2192, Japan
b Department of Cardiovascular Medicine, Kyoto University Graduate School of Medicine, Kyoto, Japana r t i c l e i n f o
Article history:
Received 29 October 2012
Received in revised form
18 December 2012
Accepted 25 January 2013
Available online 28 March 2013
Keywords:
J-wave syndrome
KCNJ8
Idiopathic ventricular ﬁbrillation
Japanese76/$ - see front matter & 2013 Japanese Hea
x.doi.org/10.1016/j.joa.2013.01.013
nts: This work was supported, in part, by
h from the Ministry of Education, Culture, Sp
the Ministry of Health, Labor and Welfare o
sures for Intractable Diseases and Translation
irculation Society (to MH).
viations: Br, Brugada; ECG, electrocardiogra
plantable cardioverter-deﬁbrillator; IVF, idiop
e
esponding author. Tel./fax: þ81 77 548 2213
ail address: horie@belle.shiga-med.ac.jp (M. Ha b s t r a c t
Background: J-point elevation has been demonstrated to be associated with ventricular ﬁbrillation (VF)
and has been proposed as a cause of the J-wave syndrome (JWS). A mutation of KCNJ8, S422L, was
reported as a culprit gene. This study aimed to determine the prevalence of KCNJ8 mutations in a
Japanese population with JWS or idiopathic VF (IVF).
Methods: A total of 230 probands with JWS and IVF underwent genetic screening of KCNJ8. To analyze
and compare clinical and electrocardiographic characteristics, the probands were divided into 4 groups:
Brugada (Br) pattern only, early repolarization (ER) pattern only, Br and ER patterns, and true IVF.
Results: The results of the genetic analysis revealed no S422L or other KCNJ8 mutations and indicated
no signiﬁcant difference between the groups.
Conclusion: The KCNJ8 mutation showed no association with JWS or IVF among our Japanese patients.
& 2013 Japanese Heart Rhythm Society. Published by Elsevier B.V. All rights reserved.1. Introduction
Ventricular ﬁbrillation (VF) is the most malignant arrhythmia
that causes sudden cardiac death. VF, which occurs in apparently
healthy individuals without structural heart diseases, is regarded
as an idiopathic or primary electrical disease. Among patients
with idiopathic VF (IVF), an increased prevalence of early repolar-
ization (ER) was observed, which was considered as a benign
electrocardiographic (ECG) ﬁnding in the past [1]. Recently, the
concept of J-wave syndrome (JWS), including the ER and Brugada
(Br) syndromes, has emerged [2].
The mutation KCNJ8-S422L was ﬁrst identiﬁed as the cause of
ER syndrome in a 14-year-old Caucasian girl with VF. An ECG
showed a prominent ER pattern in the inferolateral leads [3].
KCNJ8 encodes an inward rectiﬁer potassium 6.1 protein (Kir6.1),rt Rhythm Society. Published by E
a Grant-in-Aid for Scientiﬁc
orts, Science and Technology
f Japan for Clinical Research
al Research Funds from the
m; ER, early repolarization;
athic VF; JWS, J-wave
.
orie).which is a subunit of cardiac ATP-sensitive K (KATP) channels. The
succeeding cases of the mutation were found in ﬁve men and
two women with ER or Br syndrome [4,5]. However, whether
KCNJ8mutations are present among the Asian population remains
to be known. Therefore, the present study aimed to investigate
the prevalence of KCNJ8 gene mutation in Japanese patients with
JWS or IVF.2. Method
2.1. Study population
The study population was selected from unrelated families and
consisted of 230 Japanese probands with IVF, Br syndrome, or
suspected Br syndrome. All the probands underwent genetic
analysis between 1996 and 2011 at the Shiga University of
Medical Science and Kyoto University Graduate School of Medi-
cine. Probands with structural heart diseases or other inheritable
arrhythmic disorders were excluded from the study.
2.2. DNA isolation and mutation analysis
The genetic analysis protocol was approved by the institutional
ethics committees of both universities and performed under the
respective institutional guidelines. All the patients provided informedlsevier B.V. All rights reserved.
Fig. 1. Twelve-lead ECGs representing an early repolarization (ER) pattern. (A) ER
pattern in the inferior and lateral leads. (B) ER pattern in the lateral leads only.
Arrows indicate a slurring (opened) or notching (closed) ER morphology.
Q. Wang et al. / Journal of Arrhythmia 29 (2013) 261–264262consent before undergoing the genetic analysis. Genomic DNA was
isolated from leukocyte nuclei. We performed genetic screening for
KNCJ8, SCN5A, CACNA1C, CACNB2, SCN1B, KCNQ1, KCNH2, KCNE1-3,
and KCNE5 using denatured high-performance liquid chromatogra-
phy (WAVE System Model 3500, Transgenomic, Omaha, NE, USA)
[6–8], high-resolution melting (LightCyclers480, Roche Diagnostics
GmbH, Mannheim, Germany), and direct sequencing with the ABI
PRISM 3130 sequencer (Applied Biosystems, Foster City, CA, USA).
The cDNA sequence numbering of KCNJ8 was based on the GenBank
reference sequence (NC_000012). We excluded all the probands who
had genetic test results positive for all the above-mentioned genes,
except KCNJ8.
2.3. Clinical phenotype
We analyzed the following demographic characteristics in 230
patients: sex, age at diagnosis, history of symptoms, and indica-
tion for treatment with an implantable cardioverter-deﬁbrillator
(ICD). Patients who had a history of syncope or aborted cardiac
arrest were considered symptomatic. The presence of Br [9] and
ER patterns was examined using a 12-lead ECG. PR intervals, QRS
durations, and QT intervals were manually measured in lead V5.
QTc intervals were calculated by correcting for heart rate using
the Bazett formula. Patients in whom QTc values in resting ECG
were lower than 350 ms1/2 or higher than 470 ms1/2 (men) and
480 ms1/2 (women) were also excluded [10].2.4. Data analysis
The patients with JWS were stratiﬁed into 4 groups according
to the following ECG characteristics: Br pattern only [9] (Br
group), ER pattern only (ER group), overlapping Br and ER
patterns (Br–ER group), or IVF with neither a Br nor ER pattern
(true IVF group). Patients whose ECG displayed only a Br-type ST
elevation in leads V1 through V3 [9] were categorized under the
Br-only group, regardless of whether the Br pattern was sponta-
neous or drug induced. We deﬁned ER as either a slurring or
notching J-point elevation of at least 0.1 mV from the baseline in
at least 2 conjugate leads (Fig. 1A and B) [11]. Patients who
exhibited both Br and ER patterns were assigned in the Br–ER
group, whereas those with VF/ventricular tachycardia whose ECG
showed no Br or ER pattern were assigned in the true IVF group.
2.5. Statistical analysis
All continuous data were expressed as mean7standard devia-
tion values. One-way analysis of variance with the Fisher least
signiﬁcant difference test and Games-Howell test was used for
multiple comparisons. A Po0.05 was considered statistically
signiﬁcant.3. Results
3.1. Gene analysis
The gene analysis revealed that neither KCNJ8-S422L nor other
KCNJ8 mutations were present in our Japanese JWS and IVF
cohorts. Nevertheless, we found a previously reported synon-
ymous variant, p.I37I (c.C457T, rs112604741), in 2 probands,
1 who had VF belonged to the true IVF group and the other,
who was asymptomatic, belonged to the Br–ER group. The
mutation was absent in 112 healthy controls; however, the
frequency of this SNP was reported to be 1.5% in heterozygotes
(http://www.ncbi.nlm.nih.gov/snp).
3.2. Clinical characteristics
Table 1 presents the classiﬁcation of the patients enrolled in
this study according to clinical and ECG characteristics. The data
of 230 probands (205, men) were included in the analysis. The
patients’ mean age at diagnosis was 45.1715.4 years. In terms of
ECG characteristics, 135 patients had an ECG showing a Br pattern
only; 15 an ER pattern only; and 53 Br and ER patterns. Only 27
patients with VF had no ECG abnormality.
The total clinical phenotypes are presented in Table 1. The
symptomatic group included 72 patients who had experienced
syncope and 75 who had an aborted cardiac arrest. Among the
230 probands, 88 (38%) had cardioverter-deﬁbrillator implants.
In the ECG analysis, the mean heart rate, PR, QRS, and QTc inte-
rval were 67.1713.6 bpm, 176.5725.8 ms, 94.6752.0 ms, and
404.2732.6 ms1/2, respectively. Of the 230 patients, 188 (82%)
had a Br ECG pattern (Br and Br–ER subgroups); 68 (30%), an ER
pattern (ER and Br–ER subgroups); 53, (23%), Br and ER patterns;
and 27 (12%), neither a Br nor ER pattern (true IVF).
Table 1 summarizes the clinical and ECG characteristics in the
Br, ER, Br–ER, and true IVF groups. Male patients accounted for
89%, 87%, 96%, and 78% of the patients in the groups, respectively.
The mean ages were similar in the 4 groups. Most of the ER and
true IVF patients had experienced an aborted cardiac arrest
compared with the Br and Br–ER patients (93% and 93% vs. 17%
and 25%; Po0.0001), indicating a statistically signiﬁcant differ-
ence. The reason for the difference is that most of the patients in
Table 1
Comparison of the clinical and electrocardiographic (ECG) characteristics.
Total Br only ER only Br–ER True IVF
n (%) 230 135 (59) 15 (7) 53 (23) 27 (12)
Men 205 (89) 120 (89) 13 (87) 51 (96) 21 (78)
Age (years) 45.1715.4 45.3715.5 44.2714.0 46.3714.1 42.7718.5
Symptomatic 139 (60) 66 (49) 15 (100) 31 (59) 27 (100)
Syncope 72 (31) 46 (34) 2 (13) 18 (34) 6 (22)
Aborted cardiac arrest 75 (33) 23 (17) 14 (93) 13 (25) 25 (93)
Treatment ICD 88 (38) 41 (30) 10 (67) 21 (40) 16 (60)
Heart rate (bpm) 67.1713.6 68.3714.5 63.8713.1 65.4711.7 66.4713.1
PR interval (ms) 176.5725.8 176.6724.2 167.3724.6 179.8728.9 174.6727.9
QRS duration (ms) 94.6752.0 97.8765.2 90.0717.7 88.5723.1 92.7717.5
QTc interval (ms1/2) 404.2732.6 401.2730.9 416.5755.1 401.8729.1 417.6725.4
Men 403.1733.0 400.1731.5 417.0758.1 401.6728.3 417.0725.6
Women 412.0728.2 409.6724.9 413.2744.2 405.4763.2 419.3727.4
Br, Brugada pattern; ER, early repolarization pattern; IVF, idiopathic ventricular ﬁbrillation.
The values are presented as n (%) and mean7SD. PR, QRS and QTc were calculated in lead V5.
Q. Wang et al. / Journal of Arrhythmia 29 (2013) 261–264 263the ER and true IVF groups were immediately hospitalized after
the ﬁrst attack, whereas most of the Br patients were receiving
medication based on an ECG abnormality during the asympto-
matic stage. However, no signiﬁcant differences were observed in
heart rate, PR interval, and QRS duration. Regarding QTc intervals,
the probands in the Br subgroup had slightly shorter intervals
than those in the true IVF subgroup (401.2730.9 vs.
417.6725.4 ms1/2, P¼0.052).4. Discussion
We found no KCNJ8 mutations in our 230 Japanese JWS and/or
IVF probands from unrelated families. JWS and Br syndromes are
regarded as primary electrical disorders causing VF that occur in
individuals without structural heart disease. Antzelevitch and Yan
[12] proposed the concept of JWS, in which the fundamental
mechanism of the J-point elevation is caused by an increased
transient outward current (Ito) due to a decrease in sodium or
calcium current or an increase in potassium current. Irrespective
of ECG subtypes such as the ER, Br, or Br–ER pattern, increased Ito
seems to play a central role in generating life-threatening events
in patients with JWS [13].
A KCNJ8 mutation, S422L, was identiﬁed in 6 probands and
1 family member with JWS [3–5]. The probands consisted of 4 Br
syndrome and 2 ER patients. Functional analyses showed that this
hotspot mutation increased the activity of cardiac ATP-sensitive
K current (IK-ATP), which resulted in the AP notch accentuation in
collaboration with epicardial Ito, and then caused a larger J-wave
and/or ST-segment elevation on the patients’ ECGs. In our cohort,
however, we failed to identify a KCNJ8mutation. This ﬁnding may
be related to the difference in ethnicities between Asian and
Western countries.
Recently, 2 novel KCNJ8 mutations, E322del and V346I, were
reported in cases of sudden infant death syndrome [14]. In the
functional analysis, both mutations displayed a decrease in IK-ATP,
which was opposite to the effect of S422L mutation on IK-ATP [4,5].
Therefore, JWS and sudden infant death syndrome seemed to
have different underlying mechanisms, though having the same
culprit gene, KCNJ8.
Based on our subgrouping according to ECG patterns, men
were predominant in the Br, ER, or Br–ER group compared with
the true IVF group (Table 1). This sex difference was also noted in
previous reports [15–17] and may be partially due to different
levels of Ito channel expression between sexes [18]. In this regard,
we recently reported that 2 novel KCNE5 mutations produced
gain-of-function effects on Ito [19]. Because KCNE5 is located inthe X-chromosome, it is interesting that all 3 male mutation
carriers were symptomatic and 2 of them displayed Br, whereas
only 2 of the 8 female carriers were symptomatic, none of whom
had a Br pattern.
4.1. Study limitations
The ER or Br ECG pattern is known to ﬂuctuate temporarily. If a
patient had an ER pattern, for example, among several ECG records,
we stratiﬁed the patient in the ER subgroup (Table 1). However, in
some cases, only 1 ECG was available; therefore, it was difﬁcult to
exclude the possibility of missing speciﬁc ECG patterns that might
have been detected by multiple ECG recordings. The ER pattern has
been reported to be predominant in 5–10% of general populations
[20–22]. A total of 112 controls underwent genetic testing for KCNJ8,
but their clinical data were not available because of complete
anonymity. Some of them may have had an ER ECG pattern. One
possible reason why we were not able to identify any KCNJ8
mutation within our cohort is that the number of our patients
(n¼230) might have been relatively small.5. Conclusion
We identiﬁed no KCNJ8 gene mutation in our IVF and JWS
patients. Therefore, KCNJ8 seemed to be not a major gene
responsible for the JWS or IVF cases in Japan.Conﬂict of interest
NoneAcknowledgments
We thank the patients for their participation in this study.
We thank Arisa Ikeda for helping with the genetic analysis.
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Genetic screening of KCNJ8 in Japanese patients with J-wave syndromes or idiopathic ventricular fibrillation 

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Genetic screening of KCNJ8 in Japanese patients with J-wave syndromes or idiopathic ventricular fibrillation

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