De Novo Mutation in the SCN5A Gene Associated With
Early Onset of Sudden Infant Death
Horst Wedekind, MD; Jeroen P.P. Smits, MD; Eric Schulze-Bahr, MD; Raoul Arnold, MD;
Marieke W. Veldkamp, PhD; Thomas Bajanowski, MD; Martin Borggrefe, MD, FESC;
Bernd Brinkmann, MD; Irene Warnecke, MD; Harald Funke, MD; Zahurul A. Bhuiyan, MD, PhD;
Arthur A.M. Wilde, MD, FESC; Günter Breithardt, MD, FESC; Wilhelm Haverkamp, MD
Background—Congenital long QT syndrome (LQTS), a cardiac ion channel disease, is an important cause of sudden
cardiac death. Prolongation of the QT interval has recently been associated with sudden infant death syndrome, which
is the leading cause of death among infants between 1 week and 1 year of age. Available data suggest that early onset
of congenital LQTS may contribute to premature sudden cardiac death in otherwise healthy infants.
Methods and Results—In an infant who died suddenly at the age of 9 weeks, we performed mutation screening in all
known LQTS genes. In the surface ECG soon after birth, a prolonged QTc interval (600 ms1/2) and polymorphic
ventricular tachyarrhythmias were documented. Mutational analysis identified a missense mutation (Ala1330Pro) in the
cardiac sodium channel gene SCN5A, which was absent in both parents. Subsequent genetic testing confirmed paternity,
thus suggesting a de novo origin. Voltage-clamp recordings of recombinant A1330P mutant channel expressed in
HEK-293 cells showed a positive shift in voltage dependence of inactivation, a slowing of the time course of
inactivation, and a faster recovery from inactivation.
Conclusions—In this study, we report a de novo mutation in the sodium channel gene SCN5A, which is associated with
sudden infant death. The altered functional characteristics of the mutant channel was different from previously reported
LQTS3 mutants and caused a delay in final repolarization. Even in families without a history of LQTS, de novo
mutations in cardiac ion channel genes may lead to sudden cardiac death in very young infants. (Circulation. 2001;104:
1158-1164.)
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Key Words: long-QT syndrome n arrhythmia n death, sudden n sodium n genes
T
he congenital long-QT syndrome (LQTS) is a familial
disorder that is characterized by prolongation of the QT
interval on the surface ECG and episodes of syncope and/or
life-threatening cardiac arrhythmias, specifically of polymorphic ventricular tachycardia (torsade de pointes, TdP) and
sudden cardiac death. Six LQTS loci are known (LQTS 1 to
6), and 5 cardiac ion channel genes have been identified. The
genes at the LQTS1 (KCNQ1), LQTS2 (HERG), LQTS5
(KCNE1), and the LQTS6 (KCNE2) loci encode for potassium ion channel subunits, whereas the LQTS3 gene
(SCN5A) encodes for an a-subunit of the cardiac sodium
channel.1
role for the LQTS associated with sudden cardiac death in
infants has been reported,2,3 and 3 recent reports also support
the theory by identifying cardiac ion channel gene mutations
in infants with aborted or experienced sudden infant death
syndrome (SIDS).4 – 6 SIDS is defined as a sudden death,
unexpected by clinical history, of an otherwise healthy infant
in whom a thorough postmortem examination fails to detect
an adequate cause of death. After the decline in infectious
diseases, SIDS is the leading cause of death in the postneonatal period.7 The pathogenesis of SIDS is multifactorial, but
the cardiorespiratory system and the central nervous system
play a major role. Investigation of the LQTS genes in infants
with SIDS or infants with premature sudden death has not
been conducted systematically so far because tissue samples
often are not available. The genetic information obtained
from such infants may provide us with new clues of the
See p 1092
Cardiac arrhythmias as the cause for syncope and sudden
death in children and young adults are well known. A special
Received March 16, 2001; revision received June 22, 2001;accepted June 28, 2001.
From the Department of Cardiology and Angiology (H.W., E.S.B., M.B., G.B., W.H.) and the Institute of Legal Medicine (T.B., B.B.), University of
Münster, Germany, the Institute for Arteriosclerosis Research (H.W., E.S.B., M.B., H.F., G.B., W.H.) at the University of Münster, Germany, the
Department of Pediatrics (R.A., I.W.), University of Mannheim, Germany, and the Experimental and Molecular Cardiology Group, Amsterdam (J.P.P.S.,
M.W.V., A.A.M.W., Z.A.B.), Academic Medical Center, University of Amsterdam, The Netherlands.
Drs Horst Wedekind, Jeroen P.P. Smits, and Raoul Arnold contributed equally to this study.
Correspondence to Dr med Horst Wedekind, Westfälische Wilhelms-Universität Münster, Innere Medizin C, Kardiologie/Angiologie, AlbertSchweitzer-Str 33, 48149 Münster, Germany. E-mail hwede@uni-muenster.de
© 2001 American Heart Association, Inc.
Circulation is available at http://www.circulationaha.org
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Wedekind et al
De Novo SCN5A Mutation and Sudden Cardiac Death
pathogenic background in SIDS cases and will also address
the question of the heritable factors as a cause for sudden
infant death.
To date, more than 130 mutations in the LQTS genes have
been identified; the majority of them are localized in the two
cardiac potassium channels genes, KCNQ1 (LQTS1) and
HERG (LQTS2). Mutations in the SCN5A gene (LQTS3)
account for only 10% to 15% of all yet identified mutations
in LQTS.8,9 Genotype-phenotype correlations suggest that
patients with LQTS3 mutations have significantly more
severe clinical events because the overall number of cardiac
deaths in the LQTS 1 to 3 subgroups are similar, but the
frequency of events in LQTS3 is lower.10
In this article, we report a case of a sudden cardiac death in
the third month of life caused by malignant tachycardia. We
identified a de novo mutation in the SCN5A gene, and the
electrophysiological data of the mutation suggest a possible
new mechanism of affecting channel activity that leads to QT
prolongation.
Methods
Genetic Analysis
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Genomic DNA was isolated from venous EDTA blood of the infant
and the family members by means of standard procedures.11 Genetic
studies were performed in concordance with the recommendations of
the ethics committee of the university and by the agreement of the
parents. PCR primers were used as previously reported to amplify
the entire coding regions of the 5 known LQTS genes.12,13 For both
single-stranded conformational polymorphism (SSCP) and sequencing, a touchdown PCR was used with the “hot start” technique.14
Mutation Analysis With Fluorescent SSCP
SSCP analysis was performed according to the recommendations of
the manufacturer (Amersham Pharmacia Biotech). Fluorescencelabeled PCR primers were used to amplify all coding exons and
exon/intron boundaries of KCNQ1 HERG, SCN5A, KCNE1, and
KCNE2. PCR products were analyzed with the A.L.F. Express DNA
Sequencer (Amersham Pharmacia Biotech) connected to an external
temperature control device; 3 mL of the PCR product was added to
1.5 mL of 50-bp/300-bp sizer and 4.5 mL of denaturing solution
(formamide and 0.01% bromophenol blue). This mixture was incubated for 3 minutes at 98°C; 4 mL was applied to a 6% polyacrylamide gel (acrylamide/bisacrylamide, 99:1). Each exon was analyzed
at 12°C and 18°C, and mutations were detected by differences in
migration patterns compared with the wild type.
Mutation Analysis by Gene Sequencing
Sequence analysis was done with the use of a solid-phase template
preparation procedure, which requires that one of the primers used
for PCR is biotinylated. To prepare single-stranded DNA,
streptavidine-covered paramagnetic particles (Dynabeads M-280,
Dynal) were used as recommended by the supplier. The immobilized
template was sequenced with nested fluorescence-labeled primers,
following the instructions of the AutoRead T7 Sequencing Kit
(Amersham Pharmacia Biotech). DNA electrophoresis and sequence
analysis were performed on the A.L.F. DNA-sequencer.
Confirmation of Paternity
In the index patient, paternity was proved by means of 10 highly
polymorphic microsatellite markers (AmpFlSTR Profiler Amplification Kit; Applied Biosystems). Fragment analysis was performed on
an ABI Prism 310 Genetic Analyzer (Applied Biosystems) with
internal length standards.
1159
Site-Directed Mutagenesis
Mutant Na1 channel cDNA was prepared by mutagenesis on the
pSP64T-hH1 plasmid.15 Primers used for the site-directed mutagenesis were 59-CAATGCCCTGGTGGGCCCCATCCCGTCCATC-39
and 59-CATGATGGACGGGATGGGGCCCACCAGGGCA-39. An
AccI–KpnI fragment was subcloned into wild-type pSP64T-hH1, and
the mutant insert and ligation regions were completely analyzed by
sequencing. The A1330P cDNA was then subcloned into the
HindIII-XbaI sites of the expression vector pCGI (kindly provided by
David Johns and Eduardo Marbán, Johns Hopkins University,
Baltimore, Md) for bicistronic expression of the channel protein and
GFP reporter in a Human Embryonic Kidney cell line (HEK 293).
Heterologous Expression of the Mutant
Sodium Channel
To express mutant (A1330P) and wild-type (WT) hH1, HEK 293
cells were cotransfected with 2 mg of Na1 channel a-subunit cDNA
(WT or mutant, respectively) and 2 mg hb1-subunit cDNA with the
use of lipofectamine (Gibco BRL, Life Technologies). Transfected
HEK 293 cells were cultured in minimum essential medium (Earles
salts and L-glutamine) supplemented with nonessential amino acid
solution, 10% fetal bovine serum, 100 IU/mL penicillin, and 100
mg/mL streptomycin in a 5% CO2 incubator at 37°C for 1 or 2 days.
Only cells exhibiting green fluorescence were selected for further
electrophysiological experiments.
Electrophysiology
Sodium currents were measured in the whole-cell configuration of
the patch-clamp technique with the use of an Axopatch 200B
amplifier (Axon Instruments) with 70% to 80% of the series
resistance compensated and the following solutions (mmol/L): bath
(external) solution: NaCl 140, KCl 4.7, CaCl2 1.8, MgCl2 2.0,
NaHCO3 4.3, Na2HPO4 1.4, glucose 11.0, HEPES 16.8, pH adjusted
to 7.4 (25 mmol/L NaOH); pipette (internal) solution: CsF 100, CsCl
40, EGTA 10, NaCl 10, MgCl2 2.0, HEPES 10, pH adjusted to 7.3
(25 mmol/L NaOH).
Electrophysiological experiments were carried out at a room
temperature of 21°C. Patch electrodes were pulled from borosilicate
glass, heat-polished, and had a tip resistance of 2 to 3 MV when
filled with pipette solution. Whole-cell currents were filtered at 5
kHz and digitized at 30 kHz. Voltage control, data acquisition, and
analysis were accomplished by use of custom software.
The presence of a persistent inward sodium current was determined from the tetrodotoxin (Alomone Labs, Israel) (TTX)-sensitive
current, by taking the average current amplitude during the last 50
ms of a 300-ms depolarization to 220 mV, relative to the holding
current at 2120 mV. Only those experiments were analyzed
in which no shift in holding current was observed during wash-in
of TTX.
The voltage dependence of the relative Na1 conductance activation, steady-state inactivation, and recovery from inactivation were
determined by means of the voltage protocols as depicted in the
figures. For all protocols, the holding potential was 2120 mV and
the pulse protocol cycle time was 5 seconds. Steady-state activation
and inactivation curves were fit using the Boltzman equation:
I/Imax5A/{1.01exp[(V1/22V)/k]} to determine V1/2 (membrane
potential for the half maximal (in)activation) and the slope factor k.
Recovery from inactivation was analyzed by fitting the data with a
monoexponential equation: I/Imax5A[12exp(2t/t)], where t is the
recovery time interval and t is the time constant of recovery. The
time course of inactivation was fitted by a 2-exponential equation:
I/Imax5Af[1.02exp(2t/tf)]1{As[1.02exp(2t/ts)]}, where Af and
As are fractions of fast and slow inactivation components and tf and
ts are the time constants of fast and slow inactivating components,
respectively. The results are expressed as mean6SEM; statistical
analysis was done with the use of a Student’s t test for comparison
of 2 means.
1160
Circulation
September 4, 2001
Figure 1. Standard ECG recordings taken
on first (A) and fifth (B) days of life. Paper
speed 50 mm/s; 10 mm/1 mV. On day 1,
sinus rhythm with heart rate of 128 bpm
and normal atrioventricular conduction
time is shown. Although T-wave morphology with its convex-shaped progression
was abnormal, QTc interval measured at
this time was 410 ms1/2 within normal limits. In contrast, ECG taken on day 5
showed marked QTc prolongation of 600
ms1/2 with late-onset peaked T-wave.
Heart rate under newly initiated b-blocker
therapy was 107 bpm.
Downloaded from http://ahajournals.org by on December 5, 2021
Results
Clinical Presentation
The male infant was born after 39 weeks of gestation, with a
body weight of 3910 g. He was the full-term product of a
normal pregnancy, labor, and delivery. Apgar score was 9 at
5 and 10 minutes. The initial physical cardiovascular examination in the nursery was normal. The pulse was 130 to 160
bpm, blood pressure was 90/50 mm Hg, and body temperature was 36.9°C. At the first day of life, the newborn had
recurrent episodes of sudden cyanosis and unconsciousness.
Loud screams proceeded each episode. At the neonatal
intensive care unit, ECG monitoring showed nonsustained
runs of a ventricular tachycardia with a heart rate of '300
bpm. The routine standard ECG taken at that time showed
sinus rhythm, normal atrioventricular and intraventricular
conduction time without QTc prolongation (Figure 1A); in
subsequent ECG recordings, a prolonged QTc interval of 600
ms1/2 calculated according to Bazett’s formula16 (Figure 1B)
was found that persisted. Furthermore, an apparent T-wave
alternans and an increased QT dispersion was documented in
the Holter monitoring (not shown). Conduction disturbances
were not detected. There was no evidence for underlying
heart disease. Physical examination including auditory evaluation was within regular limits. Serum levels of sodium,
potassium, magnesium, and calcium were in the normal
range.
The nonsustained tachycardias resembled typical TdP;
therefore, oral propanolol therapy was initiated with a dosage
of 5 mg/kg per day. Heart rates were 127 bpm on day 1 and
107 bpm under b-blocker therapy on day 5, respectively.
Within the next 7 weeks in the hospital, the infant remained
asymptomatic in stable sinus rhythm; the minimal heart rate
was 80 bpm. The tachycardia did not reappear, and the boy
was discharged at 7 weeks with oral propanolol therapy (5
mg/kg per day) and a recommendation of home monitoring.
At 9 weeks the patient had a lethal tachyarrhythmia that
was recorded by the home monitor (Figure 2). Cardiopulmonary resuscitation was performed by both parents and by
medical emergency service but was finally unsuccessful. In
the preregistered monitor recordings, recurrent bradycardias
with a heart rate of 60 bpm were also documented (data not
shown), which finally set up into TdP.
The clinical examination of the family (parents and
brother) was completely inconspicuous. The history revealed
no episode of tachycardias, syncopes, or sudden unexpected
deaths. The 12-lead ECG with measurement of the QT
interval corrected for heart rate (QTc) was within normal
range (Figure 3).
Wedekind et al
De Novo SCN5A Mutation and Sudden Cardiac Death
1161
Figure 2. Home-monitor strip during sleep with
fatal nonterminating TdP episode at age 9
weeks. Heart rate was '300 bpm. Tachycardia,
breathing, and cardiovascular parameters are
documented.
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Genetic Analysis and Paternity Confirmation
Electrophysiological Data
All exons of the LQTS genes (KCNQ1, HERG, SCN5A,
KCNE1, and KCNE2) were first screened by SSCP analysis.
In exon 23 of the SCN5A gene, an abnormal migration pattern
could be identified (Figure 4A). Subsequent sequencing of
the corresponding amplicon identified a heterozygous nucleotide exchange at codon 1330 of the gene. The G-to-C
transversion leads to an amino acid exchange from alanine to
proline (Ala1330Pro) (Figure 4B). To exclude a possible
polymorphism at this position, we tested the general population as determined by SSCP analysis in 150 unrelated healthy
individuals (data not shown) in whom the abnormal pattern
was absent.
Subsequent SSCP and sequence analysis of the parents’
and the brother’s DNA failed to identify the mutation (Figure
4A). Paternity analysis showed that the proband shared all
alleles from each of his parents (data not shown) and thus
confirmed paternity. The Essen-Möller value of paternity
confirmation was determined to be 6.299 (paternity index of
5000), which corresponds to a 99.98% probability of paternity. Taken together, A1330P represented a de novo mutation
in the infant.
First we tested whether the A1330P mutation also promotes a
persistent inward sodium current, as observed for most
LQTS3 mutations identified to date. WT (Figure 5A) and
A1330P (Figure 5B) sodium currents (INa) were recorded at
220 mV, from a holding potential of 2120 mV during
control condition and in the presence of 30 mmol/L TTX.
Neither WT nor A1330P INa showed a substantial persistent
inward component at the end of a 300-ms depolarization (see
TTX-sensitive current, inset in Figure 5). The INa amplitude at
the end of the 300-ms depolarization was 0.3860.15% (n53)
of the peak inward current for WT channels and 0.1360.02%
(n53) for A1330P mutant channels.
Next we investigated the activation and inactivation kinetics for both channel types. Figure 6 shows the current-voltage
relation and the conductance-voltage and steady-state inactivation curves for WT and mutant channels. For both channel
types, the threshold of activation was 260 mV and maximum
peak inward current was observed at 225 mV (Figure 6A, B).
There was no statistical difference between peak current
amplitude of WT and the mutant at any voltage.
Figure 6C shows that the potential for half-maximal
activation and slope factor were similar for WT and A1330P
Figure 3. Pedigree of family with sudden
infant death. Patient who died is indicated by solid square. Both parents and
older brother had normal QTc intervals;
whereas patient affected by sudden cardiac death in third month of life had prolonged QTc interval.
1162
Circulation
September 4, 2001
Figure 4. A, Fluorescent SSCP analysis of amplified exon 23 of
SCN5A is shown. Fragment shift is observed in infant with sudden cardiac death (SCD), which is absent from other investigated family members. B, Sequence analysis of exon 23 of
SCN5A. Corresponding to fragment shift in SSCP analysis, heterozygous G-to-C transversion at nt 4138 in infant with sudden
cardiac death is shown that causes amino acid alteration
(Ala1330Pro); this missense mutation was absent in other family
members (data not shown).
Downloaded from http://ahajournals.org by on December 5, 2021
mutant channels (WT: V1/25242.862.9 mV, k56.860.8
(n57); A1330P: V 1/2 5244.361.5 mV (P50.66),
k57.360.5 (P50.57), (n57)). In contrast, the V1/2 for inactivation of A1330P mutant channels was significantly shifted
to more positive potentials compared with WT channels, from
298.161.9 mV (WT, n57) to 289.862.2 mV (n57,
P,0.05). The slope factors, k, were similar: k525.860.3
and 26.160.13 for WT and A1330P, respectively. The
positive shift in steady-state inactivation produced a greater
overlap of activation and inactivation relations, the so-called
“window current.” This is illustrated in an enlargement of the
window region (see inset Figure 6D). This region for WT
channels ranged from 280 mV to 260 mV, with a maximum
of 2%, whereas that of A1330P mutant channels ranged
between 280 mV and 250 mV, with a maximum of 4%.
To compare the time course of inactivation for both
channel types, current decay was fitted with a double exponential function. Figure 7 shows that the time constants of
both fast and slow inactivation were found to be slower in the
A1330P mutant, although only significant at voltages positive
Figure 6. A, Whole-cell sodium current traces from both WT
and mutant. B, Average current-voltage relation for WT and
A1330P mutant. C, Voltage-dependent properties of activation
and inactivation for WT and A1330P sodium channels. Voltageclamp protocols are shown as inset. Data were fitted by Boltzman function. For values, see text. D, Inset shows increased
window current in voltage range from 290 to 250 mV.
to 220 mV, for example, WT: tf50.7 ms60.1, ts54.960.8;
A1330P: tf51.160.1, ts58.560.6 (P,0.05) at 110 mV
(Figure 7).
We also investigated the recovery from inactivation by
using a 2-pulse protocol. Figure 8 shows the fraction of
channels that had recovered from inactivation after various
time intervals at 2120 mV. A1330P mutant showed significantly faster recovery from WT channels (WT: t517.262.0
ms versus t510.061.7 ms for A1330P, P,0.05).
Discussion
In this report, we describe the sudden cardiac death of an
infant at 9 weeks of age who died of documented TdP
degenerating into ventricular fibrillation. The clinical diagnosis of LQTS was already made on day 2 after birth because of
a prolonged QTc of 600 ms1/2 and recurrent TdP tachycardias
for which the boy was immediately treated with oral propanolol. In addition, the infant had a number of other ECG
characteristics that have been associated with SCN5A-linked
forms of congenital LQTS, including delayed T-waves at rest
after a long isoelectric ST-segment, exercise-induced QT
interval shortening and TdP during sleep concomitant with
bradycardia.17–19
Figure 5. Whole-cell Na1 currents for wild-type
(A) and A1330P mutant (B) during 300-ms
depolarization from holding potential of 2120
before and after addition of 30 mmol/L TTX.
Insets, TTX-sensitive current obtained by
subtraction.
Wedekind et al
De Novo SCN5A Mutation and Sudden Cardiac Death
Figure 7. Fast and slow time constants of current decay as
acquired by fitting current decay at each potential with biexponential function. Asterisk indicates significance (P,0.05); solid
symbols, A1330P; and open symbols, WT.
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In most newborns and infants who had ventricular
tachycardia with poor outcome, preexisting clinical or subclinical heart disease has been identified.20 Besides conditions
such as myocarditis, cardiomyopathy, and congenital heart
disease, the LQTS has also been described as the underlying
cause for death.2,3,21 The majority of cardiac deaths caused by
LQTS still occur in teenagers and adults. Deaths during the
first months of life are uncommon.22 Our case demonstrates
such a rare form as a cause for sudden infant death.
We identified a missense mutation (A1330P) in the
DIIIS4-S5 region of the human cardiac sodium channel
a-subunit gene SCN5A. The mutation causes a substitution
from alanine to proline, which is well recognized for its
ability to disrupt protein secondary structure (particularly
within a-helices). Unlike other amino acids, its side chain is
covalently bound to the carbon, generating a rigid ring.23 At
present, 16 SCN5A mutations have been identified and linked
to the LQTS. Of these, 7 mutations (N1325S, DKPQ,
R1623Q, R1644H, E1784K, D1790G and 1795insD) have
been characterized in heterologous expression systems and
were all found to cause a late component of sodium current by
multiple mechanisms involving the inactivation process.12,24 –32 It has been predicted that such a sustained sodium
current during plateau phase of the action potential will
prolong repolarization and thus accounts for the long QT
interval. For the D1790G LQTS3 mutation, the mechanism of
QT prolongation is debated.25 Besides a persistent inward
sodium current, it displays a negative shift in voltage dependence of inactivation and may prolong the action potential
through a calcium-dependent mechanism.33
Thus, together with its localization in the DIIIS4-S5
domain close to the proposed docking site mediating inactivation, one would expect the A1330P mutant to have similar
alterations in electrophysiological properties as previously
published LQTS3 mutants. Nevertheless, the A1330P mutant
did not exhibit a detectable persistent inward current. Instead
we observed an 8.3-mV shift in the voltage dependence of
steady-state inactivation toward more positive values,
whereas voltage dependence of activation was unaffected.
This shift in inactivation predicts an increased channel
availability at the resting membrane potential of ventricular
cells but more importantly, an increase in the amplitude and
voltage range of the so-called sodium “window current,” that
1163
is, the maintained inward sodium current caused by an
overlap in activation and inactivation relations. Besides, we
found alterations in the inactivation kinetics and the recovery
from inactivation. Mutant channels exhibited a significantly
slowed rate of current inactivation at potentials positive to
220 mV, whereas recovery from inactivation (at 2120 mV)
was accelerated. These results suggest that the A1330P
mutation prolongs ventricular repolarization by an increase in
sodium current during the plateau of the action potential
caused by a slowing of the rate of inactivation and by an
increase in the window sodium current during the final phase
of repolarization. In summary, the A1330P mutant is distinguished from previous LQTS3 mutants by the absence of a
persistent inward current at depolarized potentials and a
positive shift in the voltage dependence of inactivation. (so
far, shifts in inactivation reported for LQTS3 mutants were
negatively directed).
Zareba and coworkers10 showed that patients with mutations in the SCN5A gene are associated with more lethal
cardiac events compared with the overall number of cardiac
events (20%) than patients with mutations in the LQTS1 and
LQTS2 gene (4%). At the age of 40 years, mortality rates did
not appear to be different in all 3 groups. The first death that
occurred in this LQTS3 group was documented at the age of
8 years. Before this age, only LQTS1 mutation carriers had
lethal events. In the present case, sudden arrhythmogenic
death occurred at the age of 9 weeks, which raises the
possibility that deaths associated with SCN5A mutations may
be more frequent than recently estimated by Zareba and
coworkers10 because of the exclusion for premature death of
those cases from follow-up studies. This might lead to
underestimation of the real incidence of LQTS3 patients in
this age group. Early diagnosis and treatment of infants with
LQTS is important because sudden cardiac death is more
likely to occur as the initial and final event in children than in
adults.34 Genetic analysis of the LQTS genes in neonates is
therefore recommended in those cases in whom the suspicion
of LQTS is made by family history or ECG findings including QTc at birth .500 ms1/2 or prenatal sinus bradycardia.35,36
Sporadic cases escape early diagnosis and treatment until the
infant has the first symptoms or is discovered by other
medical investigations by chance.
In summary, we identified a novel de novo mutation in the
SCN5A gene in an infant with cardiac death in the third month
of life. The electrophysiological data suggest a possible new
Figure 8. Time course of recovery from activation with 2-pulse
protocol shown in inset.
1164
Circulation
September 4, 2001
mechanism of affecting channel activity that leads to QT
prolongation. Thus, the clinical presentation and the genetic
and electrophysiological findings make this mutant very
likely to cause the disease. Even in families without a history
of LQTS, de novo mutations in cardiac ion channel genes
may cause sudden infant death and, in extrapolation, the role
of sporadic cases in SIDS must be further evaluated.
Acknowledgments
This work was supported by grants from the IMF (Innovative
Medizinische Forschung, We-1 to 2-II/97 to 17), University of
Münster, Germany; the Dr Adolf Schilling Foundation, Münster,
Germany; the Deutsche Forschungsgemeinschaft (Schu 1082/2-2,
SFB-556-A1), Bonn, Germany; Fondation Leducq, Paris, France;
Alfred Krupp von Bohlen und Halbach-Stiftung, Essen, Germany;
and NWO (Netherlands Organization for Scientific Research) grant
902-16-193. The authors thank members of the family for their
willing participation in this study. We also thank Bianca Foppe,
Ellen Schulze-Bahr, Thomas Wülfing, and Marieke Zekst for excellent technical assistance.
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