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aroline H. McCulley, BSc (Hons),* Jackie Crawford, NZCS,†‡

arey-Anne Eddy, BSc (Hons), MSc (Med),†§ Edwin A. Mitchell, FRACP, FRCPCH, DSc,�

ndrew N. Shelling, BPhEd, BSc (Hons), PhD,†§ John K. French, BMedSc, MB ChB, MSc, PhD,†¶

onathan R. Skinner, MB ChB, FRACP, FRCPCH, MD,†‡ Mark I. Rees, BSc (Hons), PhD*†#

From the Department of Molecular Medicine and Pathology, Faculty of Medical and Health Sciences, University ofuckland, Auckland, New Zealand,Cardiac Inherited Disease Group, Auckland City Hospital, Grafton, Auckland, New Zealand,Greenlane Paediatric and Congenital Cardiac Services, Starship Hospital, Grafton, Auckland, New Zealand,Department of Obstetrics and Gynaecology, Faculty of Medical and Health Sciences, University of Auckland, Auckland,ew Zealand,

Department of Paediatrics, University of Auckland, Auckland, New Zealand,Department of Cardiology, and South West Sydney Clinical School (UNSW) Liverpool Hospital, Sydney, Australia,

Institute of Life Science, School of Medicine, Swansea University, Swansea, United Kingdom.

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ACKGROUND Genetic testing in long QT syndrome (LQTS) isoving from research into clinical practice. We have recentlyiloted a molecular genetics program in a New Zealand researchaboratory with a view to establishing a clinical diagnostic service.

BJECTIVE This study sought to report the spectrum of LQTS andrugada mutations identified by a pilot LQTS gene testing programn New Zealand.

ETHODS Eighty-four consecutive index cases referred for LQTene testing, from New Zealand and Australia, were evaluated. Theoding sequence and splice sites of 5 LQTS genes (KCNQ1, HERG,CN5A, KCNE1, and KCNE2) were screened for genomic variants byransgenomics denaturing high-performance liquid chromatogra-hy (dHPLC) system and automated DNA sequencing.

ESULTS Forty-five LQTS mutations were identified in 43 patients52% of the cohort): 25 KCNQ1 mutations (9 novel), 13 HERG

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4iagfi0, 2007; accepted June 21, 2007)

547-5271/$ -see front matter © 2007 Heart Rhythm Society. All rights reserved

atients had LQTS, and 3 had Brugada syndrome. Mutations weredentified in 14 patients with resuscitated sudden cardiac death: 4CNQ1, 5 HERG, 5 SCN5A. In 17 cases there was a family history ofudden cardiac death in a first-degree relative: 8 KCNQ1, 6 HERG,SCN5A, and 1 case with mutations in both KCNQ1 and HERG.

ONCLUSION The spectrum of New Zealand LQTS and Brugadautations is similar to previous studies. The high proportion ofovel mutations (40%) dictates a need to confirm pathogenicityor locally prevalent mutations. Careful screening selection crite-ia, cellular functional analysis of novel mutations, and develop-ent of locally relevant control sample cohorts will all be essential

o establishing regional diagnostic services.

EYWORDS Long QT; Mutations; Arrhythmia; Ion channels; Suddenardiac death

Heart Rhythm 2007;4:1306–1314) © 2007 Heart Rhythm Society.

utations (7 novel), and 7 SCN5A mutations (2 novel). Forty All rights reserved.

Long QT syndrome (LQTS) represents a diverse range ofisorders associated with prolonged ventricular repolariza-ion.1 After initial description in 1957,2 LQTS was regardeds a rare disorder. It is now widely accepted that the inci-ence of LQTS previously was underestimated,3 withilder clinical phenotypes being increasingly recognized.4,5

Supported by Cure Kids (Child Health Research Foundation of Newealand), the Lion Foundation, Greenlane Research and Education Fund,

he University of Auckland Vice-Chancellor Fund, and the John Neutzeund. Jackie Crawford, Clinical Service Coordinator, is funded by a bur-ary from Medtronic. Address reprint requests and correspondence:r. Jon Skinner, Paediatric and Congenital Cardiac Services, Aucklandity Hospital, Level 3, Building 32, Private Bag 92 189, Auckland 1030,ew Zealand. E-mail address: JSkinner@adhb.govt.nz. (Received April

urrent estimates are that the incidence of LQTS geneutations is 1 in 1,000 to 5,000.6,7

To date, 9 LQTS genes have been identified and aressociated with specific phenotypes of LQTS. It is clinicallyelevant to regard these different genes as triggers for indi-idual disorders, not only in their mode of presentation, butlso in their response to �-blockers and the relative risk ofudden death.8,9 Determining genotype is imperative in op-imizing treatment.

Nearly one third of LQTS gene carriers have a QTc �60 ms on electrocardiogram.10,11 Thus, genetic screen-ng is vital in identifying with certainty those at risk ofdverse events and of transmitting this risk to futureenerations. Once a causative mutation has been identi-

ed in the index case, the family members can undergo

. doi:10.1016/j.hrthm.2007.06.022

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1307Chung et al Long QT and Brugada Syndrome

ascade screening, testing for presence or absence of thenown mutation.

KCNQ1 (LQT1) and HERG (LQT2) encode �-subunitsf the voltage-gated K� channel and are responsible for IKsnd IKr, respectively. Loss of function mutations results inrolongation of the QT interval. SCN5A (LQT3) encodeshe �-subunit of a voltage-gated Na� channel. Gain ofunction mutations in SCN5A cause long QT type 3,hereas those mutations creating a loss of function result inrugada syndrome. KCNE1 (LQT5) and KCNE2 (LQT6)ode for the �-subunit of the K� channel, affecting IKs andKr, respectively.

Brugada syndrome, like LQTS, is a hereditary cause ofudden cardiac death with a variable clinical phenotype.utations in SCN5A have also been associated with sudden

nexplained nocturnal death syndrome,12 cardiac conduc-ion disorder,13 sudden infant death syndrome,14 sick-sinusyndrome,15 and dilated cardiomyopathy.16

Several LQTS genetic screening studies have been pub-ished, identifying over 600 mutations.7,17,18 In response tohe clear clinical importance of genetic screening for LQTSnd Brugada syndrome, we piloted a grant-funded univer-ity-based research program in New Zealand in 2001. Weished to identify the local spectrum of mutations and exam-

ne factors relevant to establishing a clinical genetic diagnosticervice in a relatively small population (4.2 million). Thiseport describes the spectrum of mutations identified and ourarly experience of this national pilot program.

ethodsatients suspected of having LQTS or Brugada syndromeere referred to our cardiac service. The initial presenta-

ions to medical services included personal symptoms (syn-ope, seizures, or resuscitated SCD), SCD of a relative, andhe incidental finding of a prolonged QTc interval. Thosehose history and electrocardiogram findings supported a

linical diagnosis of LQTS or Brugada syndrome proceededo molecular genetic analysis. Informed consent for geneticesting was obtained in all cases, following the protocolsstablished in our multicenter ethical approval from theegional ethics committee.

Eighty-four index cases were screened for mutations inve genes associated with LQTS: KCNQ1, HERG, SCN5A,CNE1, and KCNE2. DNA was extracted from blood sam-les using standard phenol-chloroform extraction. The cod-ng sequence and splice sites of the 5 LQTS genes werecreened for genomic variants by transgenomics dHPLCystem and automated DNA sequencing as described below.

DNA was amplified using a polymerase chain reactionPCR). The exons and flanking intron boundaries ofCNQ1 and HERG were amplified using primers fromrevious reports.19,20 Primers for SCN5A, KCNE1, andCNE2 were designed using Primer 3.0 program White-ead Institute, Cambridge, MA (http://frodo.wi.mit.edu/cgi-in/primer3/primer3_www.cgi).

Before dHPLC, PCR products were denatured at 95°C for

minutes and slowly cooled to 4°C (0.1°C/sec) using an w

utomated program on the PTC-200 PCR machine (MJ Re-earch Watertown, MA) to generate either homoduplex oreteroduplex molecules if a mismatch of base pairs wasresent.

To identify single-nucleotide polymorphisms and mutationsn LQTS genes, sequence variation was detected by dHPLCnalysis in a mixture of DNA from index cases and normalontrol samples.21 dHPLC was performed on the Trans-enomic 2100 Waver DNA fragment analysis system (Trans-enomic, Omaha, NE) using a DNASep HT cartridge andavigator version 1.5.1 software (2003, Transgenomic,maha, NE). For each amplimer assay, the optimal partialenaturing temperatures were determined using interpretationf the DNA melting properties by the Navigator version 1.5.1oftware.

PCR products of DNA samples with variant dHPLCrofiles underwent electrophoresis on 1.5% agarose gelsnd were purified with the Qiaquick PCR purification kitQiagen, Inc, Hilden, Germany). The purified DNA frag-ents were sequenced using Big Dye Terminator kits and

n ABI 3100 automated sequencer (Applied Biosystems,oster City, CA) at the Center for Gene Technology, Uni-ersity of Auckland, New Zealand.

The population frequency of single-nucleotide polymor-hisms and suspected functional variants were assessed in00 control chromosomes using restriction fragment lengtholymorphisms analysis if a suitable restriction enzyme wasvailable. Candidate mutations that failed to generateestriction fragment length polymorphism changes weressessed by dHPLC of controls vs mutation positiverofiles to test the frequency of the abnormal profileithin the control population. Variants were designated

s mutations by excluding them from normal populationontrols and aligning them against other GeneBank da-abases to assess the degree of evolutionary/phylogeneticonservation.

esultsf the 43 patients, 31 (72%) were female and 12 (28%)ere male. The median age was 21 years, with a range ofto 60 years. Ethnicity data were as follows: 31 (78%)uropean, 5 (12%) Pacific, 4 (9%) New Zealand Maori,(5%) Chinese, 1 (2%) Middle Eastern. The median

orrected QT interval was 500 ms, with a range from 450o 660 ms.

Forty-five mutations were found in 43 patients, reflectingdetection rate of 52%: 25 KCNQ1, 13 HERG, and 7

CN5A. Forty-two of these mutations, in 40 patients, wereonsistent with LQTS, whereas 3 SCN5A mutations weressociated with Brugada syndrome.

Five mutations were detected in more than 1 unrelatedndex case. In the KCNQ1 group, there were 3 patients withhe mutation L266P, 2 with R360G, and 2 with R518X. Aurther 3 patients had a D774Y mutation in HERG, and 2

ere positive for R1193Q in SCN5A. In total there were 12

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1308 Heart Rhythm, Vol 4, No 10, October 2007

nrelated index cases sharing a mutation with at least 1ther individual.

Of the 38 different mutations identified in this study, 1745%) were novel (Table 1, Figure 1), whereas 21 (55%)ere previously reported (Table 2). Novel mutations were

ound in all 3 genes: 8 in KCNQ1, 7 in HERG, and 2 inCN5A. Phylogenetic alignments for all novel missenseariants are shown in Figure 2.

Two cases of Jervell and Lange-Neilsen syndrome, as-ociated with sensorineural deafness, segregated withCNQ1 compound heterozygosity (R518X/G189fs94X) or

onsanguineous homozygosity (maternal and paternalel998-999[GT] � 2). One case of LQTS was associatedith 2 frameshift mutations in KCNQ1 (IVS10-1G¡T) andERG (Ins513[CTGCTG]).The majority of LQT1 mutations were missense muta-

ions in regions encoding transmembrane domains, particu-arly S5 and S6 regions, and the intracellular C-terminalFigure 3). Most of the HERG mutations were localized toithin intracellular N- and C-terminal domains, with 3ERG missense mutations detected in the S4 and S5 trans-embrane domains (Figure 4). The majority of SCN5Autations were identified in regions encoding intracellular

omains (Figure 5). A SCN5A mutation in the DII-DIIIinker (R1193Q) is represented in 2 Brugada cases and wasreviously identified as a determinant in a sudden unex-lained nocturnal death syndrome case.12 This mutation wasonsidered a polymorphism in certain populations22,23;owever, functional analysis of R1193Q confirms a persis-ent sodium current that can explain QTc prolongation.24 Noutations were identified in KCNE1 and KCNE2.There was a personal history of syncope in 35 (81%)

ases (Tables 3 and 4). Of these, 14 had required resusci-ation, including 7 who had received DC cardioversion.amily history was positive for sudden unexpected death infirst-degree relative at age �35 years in 17 (40%) cases.

n total, of the 43 gene-positive patients, 28 (65%) hadither a personal history of resuscitated sudden cardiaceath, a family history of sudden death, or both. In these 28atients, there were 29 mutations, of which 13 were inCNQ1, 10 were in HERG, and 6 were in SCN5A. Theseutations that were associated with severe clinical eventsade up 52% of the LQT1 mutations, 78% of the LQT2utations, 100% of the LQT3 mutations, and 67% of theutations causing Brugada syndrome. Clinical management

s not determined by the Cardiac Inherited Disease Groupnd is dependent on local cardiologist and patient prefer-nce. We are aware of 16 patients from our gene-positiveohort who were offered insertion of an implantable cardio-erter defibrillator (ICD). Of these, 14 patients proceededith ICD insertion and 2 declined. Patients offered ICDs

ncluded most of those who had suffered events requiringesuscitation and those with mutations in SCN5A. Oneatient, who had been resuscitated after near-drowning,uffered severe hypoxic ischemic encephalopathy and was

ot offered an ICD. a

iscussionenetic testing in LQTS is moving from research laborato-

ies into clinical practice. This study identifies and high-ights several issues to be considered when developing alinical diagnostic service. Substantial allelic heterogeneityn LQTS genes means molecular testing is complex, andonsideration needs to be given to the best practice forenetic screening. Our study illustrates the frequent findingf previously unclassified variants when screening LQTSenes. To aid in interpretation of these abnormalities, it isssential to establish appropriate selection criteria forcreening and to undertake careful correlation with clinicalnformation. In addition, there is a need to develop largeocally relevant control sample cohorts and to perform cel-ular functional studies to confirm pathogenicity of muta-ions.

There is clear evidence to support the need for LQTSene screening as a clinical test. Knowledge of genotype

KCNQ1 F339S

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igure 1 Panel of novel sequences: sequence panel of novel mutationsdentified in this study. The position of mutations are indicated by anrrow, and the sequence is displayed in forward direction unless markedtherwise (*).

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1309Chung et al Long QT and Brugada Syndrome

ndividuals at risk of life-threatening arrhythmia. There iso evidence showing that subjects with LQT 3 respond to-blocker therapy (unlike LQT 1 and LQT2), meaning

CDs are required for symptomatic individuals. Appropriateargeting of therapies according to genotype is the majoractor in making LQTS genetic testing cost-effective in thelinical setting.25 In addition, identifying the mutation in thendex case enables cascade screening of family members.fter detection of the LQTS mutations reported in this

tudy, we have conducted genotype testing in over 170t-risk family members.

Of the first 84 LQTS and Brugada index patientscreened in New Zealand for mutations in the coding se-uence of 5 LQTS genes (KCNQ1, HERG, SCN5A,CNE1, and KCNE2), there were 42 LQTS mutations and

igure 2 Phylogenetic alignments in A: amino acid sequence alignmentutations, C: amino acid sequence alignment of SCN5A novel mutations.

Brugada mutations detected in 43 unrelated index cases. c

his is a 52% detection rate, which is consistent with aecent study finding,7 but is slightly lower than previouslyublished PCR-based studies.17,18 The detection rate isikely to depend on the screening criteria and on the degreef pretest clinical suspicion.7

In 17 families from our gene-positive group, a suddeneath occurred. It was often many years before anotheramily member presented with or was investigated for theiagnosis of LQTS. LQTS gene mutation analysis, togetherith clinical review of the family, needs to be integrated

nto the forensic investigation of young sudden death. En-uring that there are pathways for this to occur is part ofstablishing a clinical service for LQTS testing.

The relative preponderance of KCNQ1 mutations in ourtudy, 60% (95% confidence interval 45% to 74%) of those

NQ1 novel mutations, B: amino acid sequence alignment of HERG novel

of KC

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1310 Heart Rhythm, Vol 4, No 10, October 2007

epresentative of the local population. Previous studies haveeported the percentage of KCNQ1 mutations as 42% (95%onfidence interval 37% to 47%).7,18 The recurrence of 3CNQ1 mutations in 7 unrelated index cases might well

uggest a common ancestor effect. The results could, how-ver, also reflect a referral bias: an event occurring withxercise (typical of LQT1) may be a more easily recogniz-ble clinical presentation of LQTS than an episode duringleep, for example. In addition, both New Zealand andustralia have a youth culture with a strong emphasis on

porting activity, including water-based sports.Substantial allelic heterogeneity seems to be the common

eature of global LQTS data sets,6,7,17,18,26 with the excep-ion of Finland, where 4 KCNQ1 and HERG mutationsccount for 73% LQTS cases.27 This allelic heterogeneityakes LQTS gene mutation screening an expensive and

hallenging process. Alternative methods, such as hierarchi-al gene screening and genotype-phenotype analysis, coulde considered to increase the efficiency of LQTS screen-ng.28

Hierarchical mutational analysis is based on publishedata of gene prevalence and sequentially targets the most

igure 3 Mutations in KCNQ1. A: Schematic diagram of KCNQ1 geimensional schematic representation of predicted KCNQ1 polypeptide w

igure 4 Mutations in HERG. A: Schematic diagram of HERG genomic

chematic representation of predicted HERG polypeptide with locations of HERG

ikely sites of mutation. This approach might be less expen-ive and excessive in terms of the number of assays re-uired. However, it is apparent from this and other studieshat allelic and locus compound heterozygosity exists inQTS cohorts.29,30 Without complete coding region cover-ge of at least LQT1-3 (and LQT5, 6), alternative screeningpproaches may miss those with 2 mutations. This will leado underreporting of severely affected individuals. In addi-ion, during family cascade testing, some individuals will bealsely reassured by the absence of a mutation within 1QTS gene, and yet remain at risk of sudden cardiac death

rom a mutation in another known LQTS gene.In contrast to hierarchical screening, the genotype-phe-

otype approach uses targeted screening based on the rela-ionship between the phenotype and the genotype. It isnown that the majority of LQT1 patients have eventsrecipitated by physical exercise, whereas LQT2 patientsre more likely to develop arrhythmia after emotion andQT3 patients tend to be symptomatic at rest or duringleep.8 This approach would be an attractive option forationalization of gene-testing if the genotype-phenotypeelationship in LQTS was robust. However, it is known that

structure and approximate location of pathological mutations. B: Two-tions of KCNQ1 mutations.

re and approximate location of pathogenic mutations. B: Two-dimensional

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1311Chung et al Long QT and Brugada Syndrome

able 1 Novel LQTS mutations identified in this study

equence changes ExonClassification ofmutation Predicted consequence Protein position

Patient number(refers to Table 3)

utations- KCNQ1C794T 6 Missense T265I S5 1T887C 6 Missense F296S S5/pore 2del [998-999] � 2 7 Homozygous deletion S333fs128X S6 3T1016C 7 Missense F339S S6 4A1078G 8 Missense R360G C-terminal 5,6C1363T 10 Missense H455Y C-terminal 7IVS10-1 G�T 11 Splice site alteration Altered exon splicing C-terminal 8*C1888G 16 Missense P630A C terminal 9

utations-HERGT125A 2 Missense I42N N-terminal 10ins513[6bp] 4 Insertion ins172 LL N-terminal 8*ins983[13bp] 5 Insertion R328fs24X N-terminal 11dup [1871-1881] 7 Duplication F627fs89X pore 12A1886C 7 Missense N629T pore 13del [3094-3107] 13 Deletion G1031fs27X C-terminal 14C3224T 14 Missense P1075L C-terminal 15

utations-SCN5AG569A 5 Missense R190Q D1/S2-S3 16insG[4295-4299] 24 Insertion G1434fs1X DIII S6 17†

Numbering of all mutations is based on the full-length cDNA sequence (GenBank accession numbers AF000571 (KCNQ1), U04270 (HERG), AAK74065SCN5A)), with nucleotide 1 assigned to the first base of the start cordon (ATG) in accordance with current mutation nomenclature recommendations.31

Novel locus heterozygosity (IVS10-1 G�T) in KCNQ1 and (ins513[CTGCTG]) in HERG was found in a severe case.

Identified in Brugada syndrome.

able 2 Previously reported LQTS mutations detected in this study

equence ExonClassificationof mutation

Predictedconsequence

Proteinposition Reference

Patient number(refers to Table 4)

utations- KCNQ1G136A 1 Missense A46T N terminal 17 18G502A 3 Missense G168R S2 7, 26, 30, 32 19insG567 3 Insertion G189fs94X S2-S3 7, 33 20*T797C 6 Missense L266P S5 7, 18 21,22,23G805A 6 Missense G269S S5 7, 34-36 24C905T 6 Missense A302V Pore 7, 36 25G947A 7 Missense G316E Pore 17 26G973A 7 Missense G325R S6 18, 32, 37, 38 27IVS7 -2A¡G 8 Splice site Frameshift C-terminal 27 28C1066T 8 Nonsense Q356X C-terminal 18 29C1552T 12 Nonsense R518X C-terminal 7, 18, 39-41 20*,30C1637T 13 Missense S546L C-terminal 7, 36 31G1781A 15 Missense R594Q C-terminal 7, 18, 26 32

utations-HERGC1600T 7 Missense R534C S4 7, 42, 43 33G1704C 7 Missense W568C S5 44 34G1714A 7 Missense G572S S5/pore 7 35G2320T 9 Missense D774Y C-terminal 7 36,37,38

utations-SCN5AC2074A 14 Missense Q692K DI-DII 28 39G3578A 20 Missense R1193Q DII-DIII 12, 45 40B,41†A3974G 23 Missense N1325S DIII S4-S5 7, 46 42A5302G 28 Missense I1768V DIV S6 28, 47 43

All principles are identical to those in Table 1, except a list of publications are included that describe the detection of the recurrent mutations.Heterozygous compound mutations (InsG567/R518X) were identified in a Jervell-Lange-Neilson syndrome proband.

Identified in Brugada syndrome.

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1312 Heart Rhythm, Vol 4, No 10, October 2007

able 3 Clinical information for patients in this study with novel mutations

atiento. Sequence changes Diagnosis

Age(yrs) Gender Ethnicity Syncope RSCD

Identifiedtrigger/s

QTc(ms)

SD of 1°relative

1 C794T LQT1 40 F European Y Y Rest/sibutramine 6602 T887C LQT1 14 F European 4903 del [998-999] � 2 JLNS �1 M Middle East 5004 T1016C LQT1 44 F European 500 Y5 A1078G LQT1 9 M European Y Exercise 4806 A1078G LQT1 15 F European Y Exercise (water) 6007 C1363T LQT1 38 F European 470 Y8 IVS10-1/G�T/ins513

[6bp]LQT1/LQT2 60 F European Y 520 Y

9 C1888G LQT1 13 F Pacific Y Y 5600 T125A LQT2 32 F Maori Y Y* 540 Y1 ins983[13bp] LQT2 38 F Pacific Y Y Postpartum 4802 dup [1871-1881] LQT2 37 F Chinese Y Y Stress 4803 A1886C LQT2 3 F European 500 Y4 del [3094-3107] LQT2 9 M European Y 4605 C3224T LQT2 35 F European Y Y Rest/stress 500 Y6 G569A LQT3 24 M European Y Y* 4807 insG [4295-4299] (n) Brugada 1 F European Y Intercurrent

illness450

JLNS � Jervell and Lange-Neilson syndrome; RSCD � resuscitated sudden cardiac death; SD of 1° relative � Sudden death of first-degree relative at age

35 years; Y* � required DC cardioversion.

able 4 Clinical information for patients in this study with previously reported mutations

atiento. Sequence changes Diagnosis

Age(yrs) Gender Ethnicity Syncope RSCD Identified trigger/s

QTc(ms)

SD of 1°relative

8 G136A LQT1 57 F European Y Stress 620 Y9 G502A LQT1 39 F European Y Stress 500 Y0 insG567/C1552T JLNS 26 F European Y Exercise/stress 520 Y1 T797C LQT1 35 F European Y Y* General anesthetic 5902 T797C LQT1 19 F European Y 480 Y3 T797C LQT1 12 M European Y 5204 G805A LQT1 42 M European 470 Y5 C905T LQT1 12 F Maori Y Exercise/stress 4906 G947A LQT1 8 M European Y Y* Exercise (water) 5607 G973A LQT1 53 F European 5208 IVS7 -2A¡G LQT1 35 F Maori Y Intercurrent illness 5909 C1066T LQT1 42 F European Y Exercise 5200 C1552T LQT1 3 F European Y Exercise/stress 4701 C1637T LQT1 9 M European Y Exercise (water) 480 Y2 G1781A LQT1 9 M European Y Exercise (water) 4703 C1600T LQT2 12 F Chinese Y Exercise 500 Y4 G1704C LQT2 50 F European Y Postpartum 450 Y5 G1713A LQT2 9 F Pacific Y Exercise 5106 G2320T LQT2 31 F European Y 4707 G2320T LQT2 21 F European Y Y Stress 5108 G2320T LQT2 29 F Maori Y 470 Y9 C2074A LQT3 10 M European Y Y* Rest 540 Y0 G3575A Brugada �1 M Pacific Y Y* Intercurrent illness 6001 G3575A Brugada 9 F Pacific Y Y* Rest 5302 A3974G LQT3 52 M European 460 Y3 A5302G LQT3 16 F European Y Y 630

JLNS � Jervell and Lange-Neilson syndrome; RSCD � resuscitated sudden cardiac death; SD of 1° relative � Sudden death of first-degree relative at age

35 years; Y* � required DC cardioversion.

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1313Chung et al Long QT and Brugada Syndrome

linical manifestations of LQTS are highly variable evenmong the carriers of the same mutation; patients withQT1 still may die in their sleep.

onclusionsur study identified 17 unique novel mutations and 21ifferent previously reported mutations causing LQTS. Theatter have been described in the literature with varyingevels of support for mutation pathogenicity. To date, 648ndependent mutations in LQTS genes have been reportedhttp://www.fsm.it/cardmoc/), and our data expands thisepertoire to 665 LQTS mutations. There has been a size-ble amount of previous sequencing across LQTS codingegions in other larger LQTS cohorts as well as this study.his provides additional confirmation of the unique naturef our novel mutations, despite our relatively small andnderpowered control-sample cohort. The importance of theevelopment of large locally relevant and ethnicallyatched control samples is clear. In addition, we are cur-

ently involved in comprehensive collaborative studies toharacterize the biophysical properties of the novel muta-ions, as well as those recurrent mutations without previousunctional characterization.

Thus, broadly speaking, the findings of this modest-sizedohort are consistent with those from larger cohorts. Weonfirm that any such diagnostic program must use fullcreening in index cases of at least the 3 most commonenes associated with LQTS; KCNQ1, HERG, and SCN5A.he high proportion of novel mutations (40%) dictates aeed to confirm pathogenicity for locally prevalent muta-ions. Careful screening selection criteria, cellular func-ional analysis of novel mutations, and development ofocally relevant control sample cohorts all will be essentialo establishing regional diagnostic services for LQTS.

cknowledgementshe authors thank Drs. Joanne Dixon, Hugh McAlister, and

igure 5 Mutations in SCN5A. A: Schematic diagram of SCN5A gimensional schematic representation of predicted SCN5A polypeptide w

an Crozier for allowing us to include data on their patients.

eferences1. Ackerman MJ. The long QT syndrome: ion channel diseases of the heart. Mayo

Clin Proc 1998;73:250–269.2. Jervell A, Lange-Neilson F. Congenital deaf-mutism, functional heart disease

with prolongation of the Q-T interval and sudden death. Am Heart J 1957;54:59–68.

3. Vincent GM. The long QT and Brugada syndromes: causes of unexpectedsyncope and sudden cardiac death in children and young adults. Semin PediatrNeurol 2005;12:15–24.

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