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Journal of Arrhythmia 29 (2013) 291–295
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Journal of Arrhythmia
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Case Report
Variable phenotype expression with a frameshift mutation of the
cardiac sodium channel gene SCN5A
Hiroshi Kawakami, MDa, Takeshi Aiba, MD, PhDa,n, Tadakatsu Yamada, MD, PhDb,
Hideki Okayama, MD, PhDb, Yukio Kazatani, MD, PhDb, Kyoko Konishi, MD, PhDc,
Ikutaro Nakajima, MDa, Koji Miyamoto, MDa, Yuko Yamada, MDa, Hideo Okamura, MDa,
Takashi Noda, MD, PhDa, Kazuhiro Satomi, MD, PhDa, Shiro Kamakura, MD, PhDa,
Naomasa Makita, MD, PhDd, Wataru Shimizu, MD, PhDa,e
a
Division of Arrhythmia and Electrophysiology, Department of Cardiovascular Medicine, National Cerebral and Cardiovascular Center, Suita, Japan
Department of Cardiology, Cardiovascular Center, Ehime Prefectural Central Hospital, Matsuyama, Japan
c
Department of Pediatrics, Ehime Prefectural Central Hospital, Matsuyama, Japan
d
Department of Molecular Physiology, Graduate School of Biomedical Sciences, Nagasaki University, Nagasaki, Japan
e
Department of Cardiovasuclar Medicine, Nippon Medical School, Tokyo, Japan
b
art ic l e i nf o
a b s t r a c t
Article history:
Received 7 February 2013
Received in revised form
6 March 2013
Accepted 1 April 2013
Available online 24 May 2013
Loss-of-function mutations in the cardiac sodium channel α-subunit gene SCN5A result in multiple
inherited arrhythmic syndromes. This case report describes 2 unrelated probands carrying an identical
SCN5A frameshift mutation, V1764fsX1786, who exhibited distinct clinical manifestations: progressive
cardiac conduction defect (PCCD)/Brugada syndrome (patient #1) and idiopathic ventricular fibrillation
(IVF) (patient #2). Using a whole-cell patch clamp technique, cells expressing V1764fsX1786 showed no
observable Na+ current. Therefore, a significant phenotypic overlap was found between IVF and PCCD/
Brugada syndrome in the 2 probands with the V1764fsX1786, loss-of-function frameshift mutation of the
cardiac sodium channel gene SCN5A.
& 2013 Japanese Heart Rhythm Society. Published by Elsevier B.V. All rights reserved.
Keywords:
Progressive cardiac conduction defect
SCN5A
Ventricular fibrillation
Sudden cardiac death
Electrophysiology
1. Introduction
2. Case report
Loss-of-function mutations in the cardiac sodium (Na+) channel gene have been implicated in Brugada syndrome, progressive
cardiac conduction defect (PCCD), sick sinus syndrome, and idiopathic ventricular fibrillation (IVF) [1]. In the present study, we
describe 2 unrelated index cases of PCCD/Brugada syndrome and
IVF who share an identical 1-base deletion mutation of SCN5A
resulting in a large truncation at the cytoplasmic C-terminal of the
cardiac Na channel (V1764fsX1786). Despite carrying the nonfunctional allele, the 2 probands exhibit distinct clinical manifestations and electrophysiological properties. These results support
the notion that the ultimate clinical manifestations of the cardiac
sodium channelopathies are profoundly affected by many undetermined factors, including genetic variations of genes other than
SCN5A.
2.1. Patient 1
n
Corresponding author. Tel.: +81 6 6833 5012; fax: +81 6 6872 7486.
E-mail address: [email protected] (T. Aiba).
A 47-year-old man had recurrent syncope, and his 12-lead
electrocardiogram (ECG) demonstrated a complete right bundle
branch block (QRS width 200 ms), left axis deviation, and the first
degree of atrio-ventricular block (Fig. 1A). He subsequently underwent echocardiography, coronary angiography, and left ventriculography, none of which demonstrated any structural heart diseases.
However, continuous ECG monitoring revealed an episode of sinus
arrest for 4 s. A subsequent electrophysiological study (EPS) demonstrated a prolongation of the atrio-ventricular conduction time (A-H
interval, 100 ms; H-V interval, 75 ms) and extension of sinus node
recovery time (SNRT41500 ms), but neither sustained ventricular
tachycardia (VT) nor ventricular fibrillation (VF) was induced by
programmed electrical stimulation (up to 500/280/220/210 ms from
the right ventricular apex). Based on these results, the patient was
diagnosed with advanced atrio-ventricular block and sick sinus
syndrome, and a pacemaker was implanted. Although he had no
history of obvious VT or VF during the follow-up, he had palpitations during sleep at night, and coved-type Brugada-ECG findings
1880-4276/$ - see front matter & 2013 Japanese Heart Rhythm Society. Published by Elsevier B.V. All rights reserved.
http://dx.doi.org/10.1016/j.joa.2013.04.005
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H. Kawakami et al. / Journal of Arrhythmia 29 (2013) 291–295
Fig. 1. A: 12-Lead ECG of patient #1 (proband) at 47 years of age with a complete right bundle branch block (QRS width 200 ms), left axis deviation, and the first degree of
atrioventricular block. B: ECG recordings of 12-leads and V1-3 leads on higher inter-cordial spaces (ICS) of patient #1 at 71 years of age with atrial pacing and CRBBB and
coved type ST-segment elevation (0.2 mV at V2 3rd ICS). C: Pedigree and phenotypes of the family members affected by Brugada syndrome and/or conduction disease. +,
V1764fsX1786 carrier; −, non-carrier; S.D., sudden death; and y, years.
were observed (Fig. 1B). Moreover, his father (age uncertain) had
suddenly died during sleep, as had both of his sons at 32 and 22
years old (Fig. 1C). Therefore, when he was 73 years old, a pacemaker was prophylactically upgraded to an implantable cardioverter defibrillator (ICD). In 2 years after implantation of the ICD, he
had 1 episode of nonsustained VT (CL 380 ms, 4 s), but did not
receive any appropriate ICD-shock therapy.
programmed electrical stimuli at the right ventricular apex (up
to 500/220/210 ms) induced VF. Based on these results, the patient
was diagnosed with IVF and an ICD was implanted without any
medications. The patient has not had any ICD-shock therapy
during 2-year of follow up.
2.2. Patient 2
Genetic testing was performed on these 2 unrelated probands
and family members, demonstrating the same V1764fsX1786
frameshift mutation of the SCN5A gene (Fig. 3A). The same
mutation was not found in the #1 patient's brother and 2 grandsons, or the #2 patient's mother. To functionally characterize the
frameshift mutation, we performed whole-cell patch clamp
recordings as previously described [2]. The mutant or wild-type
Na+ channel was heterologously expressed in tsA-201 cells, and
cells expressing mutant Na+ channel showed no observable
sodium current (Fig. 3B) showing a compatible loss-of-function
mutation.
An 18-year-old high school student had syncope during marathon training in a physical education class and had cardiopulmonary resuscitation. VF was detected and defibrillated by automated
external defibrillator (Fig. 2A), but his consciousness level did not
fully recover (Japan Coma Scale III-300). He underwent tracheal
intubation and cerebral hypothermia therapy immediately after
hospitalization. Emergency coronary artery angiography was not
performed because he had no coronary risk, lack of ST-T changes
on ECG, and no asynergy or anomalous coronary artery origin on
echocardiography. The patient recovered consciousness without
any cerebral disorder after being rewarmed. He had no family
history of sudden cardiac death. His 12-lead ECG at admission
(Fig. 2B, right panel) showed no significant ST-T changes, BrugadaECG findings, J-waves, or prolongation/abbreviation of the QT
interval. No significant change in ECG was observed during
exercise or during pharmacologic stress test (pilsicainide or isoproterenol). He had no abnormal physical or laboratory findings,
and computed tomography and magnetic resonance imaging did
not reveal any structural heart diseases such as arrhythmogenic
right ventricular cardiomyopathy and dilated cardiomyopathy.
Although the patient had episodes of spontaneous sinus bradycardia (heart rate 37/min) and atrio-ventricular block (Wenckebach type) (Fig. 2C), PCCD was excluded since he exhibited no
obvious atrio-ventricular block or bundle branch block of ECGs,
and his previous ECGs were normal (Fig. 2B, left panel). His signalaveraged ECG (SAECG) was positive, but T-wave alternans was
negative. EPS showed that the atrio-ventricular conduction time
was prolonged (AH interval, 91 ms; H-V interval, 93 ms) and
2.3. Genetic and functional analysis
3. Discussion
Mutations in the cardiac Na+ channel α-subunit gene SCN5A cause
several inherited arrhythmogenic syndromes such as long QT syndrome type 3 (LQT3), Brugada syndrome, PCCD, and sick sinus node
syndrome. [3–7] Furthermore, loss-of- function mutations in SCN5A
have been reported to be a disease gene for IVF [8]. Even with the
same mutation (e.g. E1784K) of SCN5A, different phenotypes such as
LQT3 and Brugada syndrome were observed [2]. PCCD and Brugada
syndrome present significant overlap and can coexist in the same
family and even in the same individual [9–11].
Here we identified, for the first time, 2 unrelated probands who
carried the same SCN5A frameshift mutation, V1764fsX1786, but
exhibited distinct clinical manifestations: PCCD/Brugada syndrome and IVF, suggesting overlap Na+ channelopathies.
V1764fsX1786 mutation causes an overlap phenotype between
PCCD and Brugada syndrome [12,13]. As shown in Fig. 1, patient
H. Kawakami et al. / Journal of Arrhythmia 29 (2013) 291–295
293
Patient #2 (13 y)
Patient #2 (18 y)
V1
V1
V2
V2
V3
aVR
V3
V4
aVL
V5
-
Liver cirrhosis
V4
aVL
V5
aVF
V6
V6
aVF
IVF
+
aVR
0.5 s
QRS = 98 ms
0.5 s
QRS = 132 ms
Fig. 2. A: Monitoring ECGs of patient #2 with ventricular fibrillation detected by AED. Electrical cardioversions were performed three times by AED before hospitalization.
B: 12-Lead ECGs of patient #2 at 13 years of age and 18 years of age. QRS width age-dependently increased over 6 years. C: Sinus bradycardia and atrioventricular block
(Wenckebach type) were recognized by Holter electrocardiogram. D: Pedigree and phenotypes of the family members affected by idiopathic ventricular fibrillation.
+, V1764fsX1786 carrier; −, non-carrier; and y, years.
5290delG
DI
1 2 345
DII
6
1 2 34 5
DIII
6
12 345
DIV
6
G T C A ACA T G T A C
T C A A C ATG T A C A
1 2 345
N
C
V1764fsX1786
Fig. 3. A: A single nucleotide deletion (G) at position 5290 of the SCN5A locus results in a frameshift mutation: V1764fsX1786. B: Representative whole-cell Na+ current
recordings from tsA-201 cells expressing wild type (WT) or mutant (V1764fsX1786) Na+ channels. Currents were recorded from a holding potential of −120 mV and stepped
from −90 mV to +50 mV for 15 ms in 10 mV increments.
#1 had severe conduction abnormalities, coved-type Brugada
ECG, syncope attack, and significant family history of sudden
cardiac death. It was not possible to find out whether his sons
had the frameshift mutation, as they died suddenly during sleep
at night in their 20s or 30s, which might have resulted from VF.
Conversely, patient #2 had an episode of VF without any other
inherited or structural abnormalities, and was thus diagnosed
with IVF. However, the age-dependent increased QRS duration of
his ECG, a prolonged H-V interval, and positive late potential of
the SAECG were associated with conduction abnormalities. The
timing of events were completely different for patient #1 and his
family (during sleep) and patient #2 (during exercise), but they
are consistent with the phenotype of each (Brugada syndrome
or IVF).
PCCD (Lev or Lenègre disease) manifests as progressive prolongation of cardiac conduction (P wave, PR, and QRS intervals),
and right or left bundle branch block, without ST segment
elevation or QT prolongation. These ECG changes are often
294
H. Kawakami et al. / Journal of Arrhythmia 29 (2013) 291–295
E867X
R376H
N406S
G298S D356L
E161K
DI
G1319V
DII
DIII
S1710L
G1406R
G1408R
DIV
W156X
V1763M
V1764fsX1786
6
1 2 34 5
1 2 34 5
6
6
1 2 34 5
1 2 34 5
M1766L
V1777M
R225W
D1595N
P1332L
P336L
G752R
F861fs951X
ΔK1500
I1660V
S1812X
T512I
N G514C
PCCD
T613M
PCCD + BrS
PCCD + LQT3
P2005A
C
PCCD + LQT3 + BrS
PCCD + SSS
PCCD + BrS + SSS
PCCD + BrS + IVF
Fig. 4. Schematic representation of SCN5A mutations responsible for PCCD and relevant overlap syndrome.
accompanied by an age-related degenerative process, in which
fibrosis may affect the conduction system. In young people, the
impaired Na+ channels do not cause severe conduction defect, but
with age, an increase in fibrosis in association with the genetic
defect may impair the propagation of impulses through the
conduction system and reveal the PCCD phenotype [6]. Therefore,
haploinsufficiency of SCN5A and aging have been implicated in
PCCD,[14] and a heterozygous mouse model (SCN5A+/−) has
demonstrated age-related conduction slowing and fibrosis qualitatively similar to that seen in the PCCD patients [15]. This is
relevant to the Brugada syndrome since conduction slowing is
progressively accentuated in the Brugada probands with SCN5A
mutation compared with those without SCN5A mutation [16].
Conversely, the same mutations in SCN5A (e.g. G1406R) led to
either PCCD or Brugada syndrome in a large French family [9]. As
shown in Fig. 4, more than half of the SCN5A mutations in PCCD
overlap with Brugada syndrome, SSS, and LQT3 [17,1]. PCCD often
predominates in the elderly. Makita et al. recently reported that
the age of onset of PCCD probands showed a wide-range distribution with 2 peaks in the 20s and 60s [18]; therefore, manifestation
of PCCD due to SCN5A mutations might be an age-dependent
fibrotic change.
The functional analysis of this V1764fsX1786 mutation is
shown in Fig. 3B; no current was observed, indicating severe
loss-of-function. Although we did not investigate the mechanisms
of this complete reduction in Na+ current in this mutation, Herfst
et al [19]. reported a similar frameshift mutation of SCN5A
(5280delG, A1711fsX1786) in a large cardiac conduction defect
family, demonstrating that the A1711fsX1786 mutation results in
the translation into non-function channel proteins that fail to
reach the plasma membrane. Furthermore, Meregalli et al. showed
that Na+ current reduction by frameshift or nonsense mutations is
predicted to be a complete reduction of peak Na+ current associated with the severity of conduction slowing such as longer PR
interval and more symptoms [20]. However, disease severity
among mutation carriers is highly variable, and the sodium
channel subunit β4 (SCN4B) may be one of the potential genetic
modifiers of conduction and cardiac sodium channel disease [21].
Therefore, phenotype manifestation in the loss-of-function sodium
channel mutations could interact with many factors such as age,
sex, and other modifing genes and proteins. A further genetic
study of patients or family members is important for diagnosis and
risk stratification for conduction slowing leading to sudden
cardiac death.
4. Conclusion
A significant phenotypic overlap was found between IVF and
PCCD/Brugada syndrome in 2 probands with the V1764fsX1786,
loss-of-function frameshift mutation of the cardiac Na+ channel
gene SCN5A.
Sources of funding
This work was supported by grants from the Ministry of Health,
Labour and Welfare of Japan (2010-145); Grant-in-Aid for Scientific Research on Innovative Areas (22136011 A02, Aiba) (22136007
Makita), Grant-in-Aid for Scientific Research (C) (24591086 Aiba)
from MEXT of Japan; and the Research Grant for the Cardiovascular Diseases (H24-033 Shimizu, Aiba, Makita) from the Ministry
of Health, Labour and Welfare of Japan.
Disclosures
None.
Conflict of interest
None.
References
[1] Ruan Y, Liu N, Priori SG. Sodium channel mutations and arrhythmias. Nat Rev
Cardiol 2009;6:337–8.
[2] Makita N, Behr E, Shimizu W, et al. The E1784K mutation in SCN5A is
associated with mixed clinical phenotype of type 3 long QT syndrome. J Clin
Invest 2008;118:2219–29.
[3] Chen Q, Kirsch GE, Zhang D, et al. Genetic basis and molecular mechanism for
idiopathic ventricular fibrillation. Nature 1998;392:293–6.
[4] Wang Q, Shen J, Splawski I, et al. SCN5A mutations associated with an
inherited cardiac arrhythmia, long QT syndrome. Cell 1995;80:805–11.
[5] Bennett PB, Yazawa K, Makita N, et al. Molecular mechanism for an inherited
cardiac arrhythmia. Nature 1995;376:683–5.
H. Kawakami et al. / Journal of Arrhythmia 29 (2013) 291–295
[6] Schott JJ, Alshinawi C, Kyndt F, et al. Cardiac conduction defects associate with
mutations in SCN5A. Nat Genet 1999;23:20–1.
[7] Tan HL, Bink-Boelkens MT, Bezzina CR, et al. A sodium-channel mutation
causes isolated cardiac conduction disease. Nature 2001;409:1043–7.
[8] Watanabe H, Nogami A, Ohkubo K, et al. Electrocardiographic characteristics
and SCN5A mutations in idiopathic ventricular fibrillation associated with
early repolarization. Circ Arrhythm Electrophysiol 2011;4:874–81.
[9] Kyndt F, Probst V, Potet F, et al. Novel SCN5A mutation leading either to
isolated cardiac conduction defect or Brugada syndrome in a large french
family. Circulation 2001;104:3081–6.
[10] Smits JP, Koopmann TT, Wilders R, et al. A mutation in the human cardiac
sodium channel (E161K) contributes to sick sinus syndrome, conduction
disease and brugada syndrome in two families. J Mol Cell Cardiol
2005;38:969–81.
[11] Vorobiof G, Kroening D, Hall B, et al. Brugada syndrome with marked
conduction disease: dual implications of a SCN5A mutation. Pacing Clin
Electrophysiol 2008;31:630–4.
[12] Makita N, Seki A, Sumitomo N, et al. A connexin40 mutation associated with a
malignant variant of progressive familial heart block type I. Circ Arrhythm
Electrophysiol 2012;5:163–72.
[13] Kapplinger JD, Tester DJ, Alders M, et al. An international compendium of
mutations in the SCN5A-encoded cardiac sodium channel in patients referred
for Brugada syndrome genetic testing. Heart Rhythm 2010;7:33–46.
295
[14] Probst V, Kyndt F, Potet F, et al. Haploinsufficiency in combination with aging
causes SCN5A-linked hereditary lenegre disease. J Am Coll Cardiol
2003;41:643–52.
[15] Royer A, van Veen TA, Le Bouter S, et al. Mouse model of SCN5A-linked
hereditary Lenegre's disease: age-related conduction slowing and myocardial
fibrosis. Circulation 2005;111:1738–46.
[16] Yokokawa M, Noda T, Okamura H, et al. Comparison of long-term follow-up of
electrocardiographic features in Brugada syndrome between the SCN5Apositive probands and the SCN5A-negative probands. Am J Cardiol
2007;100:649–55.
[17] Makita N. Phenotypic overlap of cardiac sodium channelopathies: individualspecific or mutation-specific? Circ J 2009;73:810–7.
[18] Makita N, Makiyama T, Seki A, et al. Clinical features and genetic basis of 63
patients with progressive cardiac conduction defect. Heart Rhythm 2012;9:
S429.
[19] Herfst LJ, Potet F, Bezzina CR, et al. Na+ channel mutation leading to loss of
function and non-progressive cardiac conduction defects. J Mol Cell Cardiol
2003;35:549–57.
[20] Meregalli PG, Tan HL, Probst V, et al. Type of SCN5A mutation determines
clinical severity and degree of conduction slowing in loss-of-function sodium
channelopathies. Heart Rhythm 2009;6:341–8.
[21] Remme CA, Scicluna BP, Verkerk AO, et al. Genetically determined differences
in sodium current characteristics modulate conduction disease severity in
mice with cardiac sodium channelopathy. Circ Res 2009;104:1283–92.