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Long QT syndrome in Sweden: founder effects and associated cardiac phenotypes
Umeå University, Faculty of Medicine, Department of Clinical Sciences, Paediatrics.
2012 (English)Doctoral thesis, comprehensive summary (Other academic)Alternative title
Långt QT syndrom i Sverige : foundereffekter och associerade kardiella fenotyper (Swedish)
Abstract [en]

Background: We aimed to increase the knowledge regarding the familial arrhythmogenic disorder Long QT Syndrome (LQTS) and its recessive variant Jervell and Lange-Nielsen Syndrome (JLNS) in Sweden, including prevalences and clinical phenotypes. A specific focus was directed towards two KCNQ1 mutations –p.Y111C and p.R518X- commonly identified in Swedish LQTS index cases.

Methods: Cases and families with LQTS (p.Y111C or p.R518X) and JLNS were recruited via regional clinical practices, national referrals to the Clinical Genetics laboratory, Umeå University Hospital, and a national inventory. Molecular genetics methods were used for case ascertainment. Clinical data was obtained via medical records, a questionnaire, and/or an interview. Electrocardiograms were manually assessed. In p.R518X heterozygotes intra-familial phenotypic variability (QTc and cardiac events) was assessed by analysis of sequence variants (modifier genes). The origins of the mutations p.Y111C and p.R518X were investigated using genealogical and haplotype analysis (microsatellite markers). In families sharing a common haplotype mutation age and associated prevalence was analyzed using ESTIAGE and DMLE computer software.

Results: We identified p.Y111C (170 mutation-carriers) and p.R518X (101 mutation-carriers) as two major causes of LQTS/JLNS in Sweden. LQTS phenotype was revealed to be relatively benign in p.Y111C and p.R518X (annual incidence of life-threatening cardiac events, before therapy 0.05% and 0.04%, respectively). Gender-specific effects of genetic modifiers on phenotypic expression were seen. A founder origin, approximately 600-700 years ago in two northern river valleys was established for p.Y111C and p.R518X, and a high prevalence of LQTS founder descendants suggested. A minimum JLNS prevalence of 1:200 000 in preadolescent Swedish children was revealed. JLNS phenotype was mainly severe, with a cumulative incidence of life-threatening cardiac events of 53% (annual incidence rate before therapy 5%) and four sudden deaths. Possible founder effects regarding four KCNQ1 mutations; p.Y111C (8%), p.R518X (50%), c.572_576del (17%) and p.Q530X (8%) together explained 83% of the JLNS mutation-spectrum in Sweden, consisting of 8 KCNQ1 mutations.

Conclusion: The high prevalence of p.Y111C- and p.R518X-related LQTS as well as JLNS revealed in Sweden could be explained by the combination of mild clinical phenotypes in heterozygotes and strong founder effects present during the population development of northern Sweden. Increased knowledge regarding the occurrence of LQTS and JLNS as well as mutation- and/or genotype-specific data constitute prerequisites for possible improvement of patient management.

Place, publisher, year, edition, pages
Umeå: Umeå universitet , 2012. , 98 p.
Series
Umeå University medical dissertations, ISSN 0346-6612 ; 1515
Keyword [en]
Long QT Syndrome, Jervell and Lange-Nielsen Syndrome, inherited arrhythmia, founder effects, clinical genetics, haplotype analysis, mutation age, founder mutation, clinical phenotype, life-threatening cardiac events, mutation-specific, KCNQ1 gene, modifier genes, sequence variants, risk stratification, risk factor, gender
National Category
Pediatrics
Research subject
Pediatrics
Identifiers
URN: urn:nbn:se:umu:diva-57724ISBN: 978-91-7459-460-7 (print)OAI: oai:DiVA.org:umu-57724DiVA: diva2:544335
Public defence
2012-09-07, E04, Biomedicinhusets suterrängplan, byggnad 6E, Norrlands Universitetssjukhus, Umeå, 13:00 (English)
Opponent
Supervisors
Available from: 2012-08-15 Created: 2012-08-14 Last updated: 2012-08-15Bibliographically approved
List of papers
1. Low incidence of sudden cardiac death in a Swedish Y111C type 1 long-QT syndrome population
Open this publication in new window or tab >>Low incidence of sudden cardiac death in a Swedish Y111C type 1 long-QT syndrome population
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2009 (English)In: Circulation: Cardiovascular Genetics, ISSN 1942-325X, E-ISSN 1942-3268, Vol. 2, no 6, 558-564 p.Article in journal (Refereed) Published
Abstract [en]

Background: A 10% cumulative incidence and a 0.3% per year incidence rate of sudden cardiac death in patients younger than 40 years and without therapy have been reported in type 1 long-QT syndrome. The Y111C-KCNQ1 mutation causes a severe phenotype in vitro, suggesting a high-risk mutation. This study investigated the phenotype among Y111C-KCNQ1 mutation carriers in the Swedish population with a focus on life-threatening cardiac events.

Methods and Results: We identified 80 mutation carriers in 15 index families, segregating the Y111C-KCNQ1 mutation during a national inventory of mutations causing the long-QT syndrome. Twenty-four mutation carriers <40 years experienced syncope (30%). One mutation carrier had an aborted cardiac arrest (1.25%). No case of sudden cardiac death was reported during a mean nonmedicated follow-up of 25±20 years. This corresponds to a low incidence rate of life-threatening cardiac events (0.05%/year versus 0.3%/year, P=0.025). In 8 Y111C families connected by a common ancestor, the natural history of the mutation was assessed by investigating the survival over the age of 40 years for 107 nonmedicated ascertained mutation carriers (n=24) and family members (n=83) born between 1873 and 1968. In total, 4 deaths in individuals younger than 40 years were noted: 1 case of noncardiac death and 3 infant deaths between 1873 and 1915.

Conclusions: The dominant-negative Y111C-KCNQ1 mutation, associated with a severe phenotype in vitro, presents with a low incidence of life-threatening cardiac events in a Swedish population. This finding of discrepancy emphasizes the importance of clinical observations in the risk stratification of long-QT syndrome.

Place, publisher, year, edition, pages
Philadelphia, PA: Lippincott Williams & Wilkins, 2009
Keyword
death, sudden, genetics, ion channels, long-QT syndrome, survival
National Category
Medical and Health Sciences
Identifiers
urn:nbn:se:umu:diva-32464 (URN)10.1161/CIRCGENETICS.108.825547 (DOI)20031635 (PubMedID)
Available from: 2010-03-11 Created: 2010-03-11 Last updated: 2017-12-12Bibliographically approved
2. Origin of the Swedish long QT syndrome Y111C/KCNQ1 founder mutation
Open this publication in new window or tab >>Origin of the Swedish long QT syndrome Y111C/KCNQ1 founder mutation
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2011 (English)In: Heart Rhythm, ISSN 1547-5271, E-ISSN 1556-3871, Vol. 8, no 4, 541-547 p.Article in journal (Refereed) Published
Abstract [en]

BACKGROUND: The Y111C/KCNQ1 mutation causes a dominant-negative effect in vitro albeit a benign clinical phenotype in a Swedish Long QT Syndrome population.

OBJECTIVE: To investigate the origin (genealogic, geographic, genetic and age) of the Y111C/KCNQ1 mutation in Sweden.

METHODS: We identified 170 carriers of the Y111C/KCNQ1 mutation in 37 Swedish proband families. Genealogical investigation was performed in all families. Haplotype analysis was performed in 26 probands, 21 family members and 84 healthy Swedish controls, using 15 satellite markers flanking the KCNQ1 gene. Mutation age was estimated using the ESTIAGE and DMLE computer softwares and regional population demographics data.

RESULTS: All probands were traced back to a northern river valley region. A founder couple born in 1605/1614 connected 26/37 families. Haplotyped probands shared 2-14 (median 10) uncommon alleles, with frequencies ranging between 0.01-0.41 (median 0.16) in the controls. The age of the mutation was estimated to 24 generations (95% CI 18; 34), i.e. 600 years (95% CI 450; 850) if assuming 25 years per generation. The number of now living Swedish Y111C mutation-carriers was estimated to ~200-400 individuals for the mutation age span 22-24 generations and population growth rates 25-27%.

CONCLUSIONS: The Y111C/KCNQ1 mutation is a Swedish LQTS founder mutation, introduced in the northern population approximately 600 years ago. The enrichment of the mutation was enabled by a mild clinical phenotype and strong regional founder effects during the population development of the northern inland. The Y111C/KCNQ1 founder population constitutes an important asset for future genetic and clinical studies.

Place, publisher, year, edition, pages
Elsevier, 2011
Keyword
Dominant-negative mutation, Founder mutation, Gene mutation, Ion channel, Long QT syndrome
National Category
Cardiac and Cardiovascular Systems
Identifiers
urn:nbn:se:umu:diva-39709 (URN)10.1016/j.hrthm.2010.11.043 (DOI)21129503 (PubMedID)
Available from: 2011-02-04 Created: 2011-02-04 Last updated: 2017-12-11Bibliographically approved
3. The Swedish long QT syndrome R518X/KCNQ1 founder population- origin and clinical phenotype: phenotypic variability partly explained by gender-specific effects of sequence variants in the NOS1AP gene
Open this publication in new window or tab >>The Swedish long QT syndrome R518X/KCNQ1 founder population- origin and clinical phenotype: phenotypic variability partly explained by gender-specific effects of sequence variants in the NOS1AP gene
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(English)Manuscript (preprint) (Other academic)
Abstract [en]

Background: Genetic modifiers have been proposed to explain phenotypic variability in the long QT syndrome (LQTS). We investigate the origin and phenotype of the worldwide common R518X/KCNQ1 mutation in Sweden, as well as possible associations between p.R518X-LQTS phenotype and previously reported modifying sequence variants in the NOS1AP, KCNH2, KCNE1, SCN5A and KCNQ1(3’UTR) genes.

Methods and Results: We identified 19 p.R518X families (101 mutation-carriers, whereof 15 Jervell and Lange-Nielsen (JLNS) cases and 86 LQTS cases). Analyses of microsatellite markers, genealogy and mutation age (ESTIAGE) identified a common northern origin ~700 years ago for 17/19 families and a high prevalence of Swedish p.R518X heterozygotes was suggested (DMLE). 

Clinical phenotype ranged from severe in JLNS to relatively benign in LQTS (QTc 576±61 ms vs. 462±34 ms, cumulative incidence of (aborted) cardiac arrest 47% vs 1%, annual non-medicated incidence rate (aborted) cardiac arrest 4% vs. 0.04%).

In p.R518X-LQTS males, two NOS1AP variants rs12143842 and rs16847548 were associated with a 29 ms QT prolongation (p=0.004), explaining 27% of QTc variability.

Three derived 3’UTR-KCNQ1 variants, previously shown to suppress gene expression in an allele-specific manner, were found to segregate with the founder mutation.

Conclusion: The R518X/KCNQ1 mutation is a Swedish founder mutation presenting with an expectedly severe phenotype in JLNS and an unusually mild phenotype in LQTS, although intra-familial variability remained. Gender-specific effects of NOS1AP sequence variants explained over a fourth of QTc variance in p.R518X-LQTS males, warranting further studies. Repressive 3’UTR-KCNQ1 sequence variants segregating within the founder haplotype could possibly contribute to its relative benignancy.

Keyword
Long QT Syndrome, Jervell and Lange-Nielsen Syndrome, founder effects, genealogy, genetics, origin, haplotype analysis, mutation age, clinical phenotype, KCNQ1 gene, modifier genes, sequence variants, risk stratification
National Category
Pediatrics
Research subject
Pediatrics
Identifiers
urn:nbn:se:umu:diva-57723 (URN)
Note
Manuskriptets titel i avhandlingen: Phenotype and origin of the Swedish long QT syndrome R518X/KCNQ1 founder population - phenotypic variability partly explained by gender-specific effects of genetic modifiers.Available from: 2012-08-14 Created: 2012-08-14 Last updated: 2012-08-15Bibliographically approved
4. Prevalence, mutation spectrum, and cardiac phenotype of the Jervell and Lange-Nielsen syndrome in Sweden
Open this publication in new window or tab >>Prevalence, mutation spectrum, and cardiac phenotype of the Jervell and Lange-Nielsen syndrome in Sweden
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2012 (English)In: Europace, ISSN 1099-5129, E-ISSN 1532-2092, Vol. 14, no 12, 1799-1806 p.Article in journal (Refereed) Published
Abstract [en]

AIMS: To explore the national prevalence, mutation spectrum, cardiac phenotype, and outcome of the uncommon Jervell and Lange-Nielsen syndrome (JLNS), associated with a high risk of sudden cardiac death.

METHODS AND RESULTS: A national inventory of clinical JLNS cases was performed. Genotype and area of origin were ascertained in index families. Retrospective clinical data were collected from medical records and interviews. We identified 19 cases in 13 Swedish families. A JLNS prevalence >1:200 000 was revealed (five living cases <10 years of age). The mutation spectrum consisted of eight KCNQ1 mutations, whereof p.R518X in 12/24 alleles. Geographic clustering of four mutations (20/24 alleles) and similarities to Norway's mutation spectrum were seen. A high prevalence of heterozygotes was suggested. Three paediatric cases on β-blockers since birth were as yet asymptomatic. Seven symptomatic cases had suffered an aborted cardiac arrest and four had died suddenly. QTc prolongation was significantly longer in symptomatic cases (mean 605 ± 62 vs. 518 ± 50 ms, P = 0.016). β-Blockers reduced, but did not abolish, cardiac events in any previously symptomatic case. β-Blocker type, dosage, and compliance probably affect outcome significantly. Implantable cardioverter-defibrillator therapy (ICD, n = 6) was associated with certain complications; however, no case of sudden death.

CONCLUSION: Founder effects could explain 83% of the Swedish JLNS mutation spectrum and probably contribute to the high JLNS prevalence found in preadolescent Swedish children. Due to the severe cardiac phenotype in JLNS, the importance of stringent β-blocker therapy and compliance, and consideration of ICD implantation in the case of therapy failure is stressed.

Keyword
Jervell and Lange-Nielsen syndrome, Founder effects, KCNQ1 gene, Cardiac phenotype, Therapy efficacy
National Category
Cardiac and Cardiovascular Systems
Identifiers
urn:nbn:se:umu:diva-56903 (URN)10.1093/europace/eus111 (DOI)22539601 (PubMedID)
Available from: 2012-06-28 Created: 2012-06-28 Last updated: 2017-12-07Bibliographically approved

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Citation style
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  • modern-language-association-8th-edition
  • vancouver
  • Other style
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  • en-GB
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  • nn-NO
  • nn-NB
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  • Other locale
More languages
Output format
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