ICD harm and benefit: risk scores applied to the Swedish ICD-treated LQTS population.

Objectives. The use of implantable cardioverter defibrillators (ICDs) in long QT syndrome (LQTS) patients is essential in high-risk patients. However, it is sometimes used in patients without high-risk profiles for whom the expected benefit may be lower than the risk of ICD harm. Here, we evaluated ICD benefit and harm by assessing risk according to risk scores and pre-ICD clinical characteristics. Design. We studied 109 Swedish LQTS patients drawn from the Swedish ICD and Pacemaker Registry with data collected from medical records. In addition to clinical characteristics, we used two risk scores to assess pre-ICD risk, and evaluated ICD benefit and harm. Results. Twenty percent of all patients received ≥1 appropriate shock with a first appropriate shock incidence rate of 4.3 per 100 person-years. A long QTc (≥550 ms) and double mutations were significantly associated with appropriate shock. Low risk scores among patients without pre-ICD aborted cardiac arrest were not significantly associated with low risk of first appropriate shock. The incidence rates of a first inappropriate shock and first complication were 3.0 and 7.6 per 100 person-years, respectively. Conclusion. Our findings on ICD harm emphasize the importance of careful individual pre-ICD consideration. When we applied two risk scores to patients without pre-ICD aborted cardiac arrest, we could not validate their ability to identify patients with low risk of appropriate shocks and patients who were assessed as having a low risk still received appropriate shocks. This further supports the complexity of risk stratification and the difficulty of using risk scores.

Transethnic Genome-Wide Association Study Provides Insights in the Genetic Architecture and Heritability of Long QT Syndrome.

BACKGROUND: Long QT syndrome (LQTS) is a rare genetic disorder and a major preventable cause of sudden cardiac death in the young. A causal rare genetic variant with large effect size is identified in up to 80% of probands (genotype positive) and cascade family screening shows incomplete penetrance of genetic variants. Furthermore, a proportion of cases meeting diagnostic criteria for LQTS remain genetically elusive despite genetic testing of established genes (genotype negative). These observations raise the possibility that common genetic variants with small effect size contribute to the clinical picture of LQTS. This study aimed to characterize and quantify the contribution of common genetic variation to LQTS disease susceptibility. METHODS: We conducted genome-wide association studies followed by transethnic meta-analysis in 1656 unrelated patients with LQTS of European or Japanese ancestry and 9890 controls to identify susceptibility single nucleotide polymorphisms. We estimated the common variant heritability of LQTS and tested the genetic correlation between LQTS susceptibility and other cardiac traits. Furthermore, we tested the aggregate effect of the 68 single nucleotide polymorphisms previously associated with the QT-interval in the general population using a polygenic risk score. RESULTS: Genome-wide association analysis identified 3 loci associated with LQTS at genome-wide statistical significance (P<5×10-8) near NOS1AP, KCNQ1, and KLF12, and 1 missense variant in KCNE1(p.Asp85Asn) at the suggestive threshold (P<10-6). Heritability analyses showed that ≈15% of variance in overall LQTS susceptibility was attributable to common genetic variation (h2SNP 0.148; standard error 0.019). LQTS susceptibility showed a strong genome-wide genetic correlation with the QT-interval in the general population (rg=0.40; P=3.2×10-3). The polygenic risk score comprising common variants previously associated with the QT-interval in the general population was greater in LQTS cases compared with controls (P<10-13), and it is notable that, among patients with LQTS, this polygenic risk score was greater in patients who were genotype negative compared with those who were genotype positive (P<0.005). CONCLUSIONS: This work establishes an important role for common genetic variation in susceptibility to LQTS. We demonstrate overlap between genetic control of the QT-interval in the general population and genetic factors contributing to LQTS susceptibility. Using polygenic risk score analyses aggregating common genetic variants that modulate the QT-interval in the general population, we provide evidence for a polygenic architecture in genotype negative LQTS.

QT correction using Bazett's formula remains preferable in long QT syndrome type 1 and 2.

BACKGROUND: The heart rate (HR) corrected QT interval (QTc) is crucial for diagnosis and risk stratification in the long QT syndrome (LQTS). Although its use has been questioned in some contexts, Bazett's formula has been applied in most diagnostic and prognostic studies in LQTS patients. However, studies on which formula eliminates the inverse relation between QT and HR are lacking in LQTS patients. We therefore determined which QT correction formula is most appropriate in LQTS patients including the effect of beta blocker therapy and an evaluation of the agreement of the formulae when applying specific QTc limits for diagnostic and prognostic purposes. METHODS: Automated measurements from routine 12-lead ECGs from 200 genetically confirmed LQTS patients from two Swedish regions were included (167 LQT1, 33 LQT2). QT correction was performed using the Bazett, Framingham, Fridericia, and Hodges formulae. Linear regression was used to compare the formulae in all patients, and before and after the initiation of beta blocking therapy in a subgroup (n = 44). Concordance analysis was performed for QTc ≥ 480 ms (diagnosis) and ≥500 ms (prognosis). RESULTS: The median age was 32 years (range 0.1-78), 123 (62%) were female and 52 (26%) were children ≤16 years. Bazett's formula was the only method resulting in a QTc without relation with HR. Initiation of beta blocking therapy did not alter the result. Concordance analyses showed clinically significant differences (Cohen's kappa 0.629-0.469) for diagnosis and prognosis in individual patients. CONCLUSION: Bazett's formula remains preferable for diagnosis and prognosis in LQT1 and 2 patients.

Implantable cardioverter defibrillator treatment in long QT syndrome patients: a national study on adherence to international guidelines.

OBJECTIVES: Implantable cardioverter defibrillator (ICD) treatment is effective among long QT syndrome (LQTS) patients at a high risk of sudden cardiac death. Previous studies show that the international guidelines are not always followed, and that risk stratification may be based on genotype rather than individual risk profile. We analysed data from the Swedish ICD & Pacemaker Registry and medical records to examine how international guidelines were followed with regards to phenotype and genotype. METHODS AND RESULTS: ICD treatment was used in 150 Swedish LQTS patients from 1989-2013. The annual number of implantations increased over the study period. A total of 109 patients were included in the analysis. Most patients (91%) were symptomatic before the implantation. Seventy percent of patients who received ICD treatment met the 2006 Class I or Class IIa recommendations for LQTS treatment. Thirty-one percent of the LQT3 patients received ICD treatment despite being asymptomatic. Among LQT1 patients, 45% received ICD treatment after syncope despite beta-blockers. CONCLUSIONS: Thirty percent of Swedish LQTS patients with ICD received the treatment without a strong indication based on international guidelines. LQT3 patients were over-represented among asymptomatic patients. Many LQT1 patients received ICD despite the known effect of beta-blockers in this group.

Phenotype, origin and estimated prevalence of a common long QT syndrome mutation: a clinical, genealogical and molecular genetics study including Swedish R518X/KCNQ1 families.

BACKGROUND: The R518X/KCNQ1 mutation is a common cause of autosomal recessive (Jervell and Lange Nielsen Syndrome- JLNS) and autosomal dominant long QT syndrome (LQTS) worldwide. In Sweden p.R518X accounts for the majority of JLNS cases and is the second most common cause of LQTS. Here we investigate the clinical phenotype and origin of Swedish carriers of the p.R518X mutation. METHODS: The study included 19 Swedish p.R518X index families, ascertained by molecular genetics methods (101 mutation-carriers, whereof 15 JLNS cases and 86 LQTS cases). In all families analyses included assessment of clinical data (symptoms, medications and manually measured electrocardiograms), genealogy (census records), haplotype (microsatellite markers) as well as assessment of mutation age and associated prevalence (ESTIAGE and DMLE computer software). RESULTS: Clinical phenotype ranged from expectedly severe in JLNS to surprisingly 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%).A common northern origin was found for 1701/1929 ancestors born 1650-1950. Historical geographical clustering in the coastal area of the Pite River valley was shown. A shared haplotype spanning the KCNQ1 gene was seen in 17/19 families. Mutation age was estimated to 28 generations (95% CI 19;41). A high prevalence of Swedish p.R518X heterozygotes was suggested (~1:2000-4000). CONCLUSIONS: R518X/KCNQ1 occurs as a common founder mutation in Sweden and is associated with an unexpectedly benign phenotype in heterozygous carriers.

Vectorcardiographic recordings of the Q-T interval in a pediatric long Q-T syndrome population.

Measurements of the Q-T interval are less reliable in children than in adults. Identification of superior diagnostic tools is warranted. This study aimed to investigate whether a vectorcardiogram (VCG) recorded from three orthogonal leads (X, Y, Z) according to Frank is superior to a 12-lead electrocardiogram (ECG) in providing a correct long Q-T syndrome (LQTS) diagnosis in children. This LQTS group consisted of 35 genetically confirmed carriers of mutations in the KCNQ1 (n = 29) and KCNH2 (n = 6) genes. The control group consisted of 35 age- and gender-matched healthy children. The mean age was 7 years in the LQTS group and 6.7 years in the control group (range, 0.5-16 years). The corrected Q-T interval (QT(c)) was measured manually (QT(man)) by one author (A.W.). The 12-lead ECG automatic measurements (QT(ECG)) and interpretation (QT(Interpret)) of QT(c) were performed with the Mac5000 (GE Medical System), and the VCG automatic measurements (QT(VCG)) were performed with the Mida1000, CoroNet (Ortivus AB, Sweden). By either method, a QT(c) longer than 440 ms was considered prolonged and indicative of LQTS. Of the 35 children with genetically confirmed LQTS, 30 (86 %) received a correct diagnosis using QT(VCG), 29 (82 %) using QT(man), 24 (69 %) using QT(ECG), and 17 (49 %) using QT(Interpret). Specificity was 0.80 for QT(VCG), 0.83 for QT(man), 0.77 for QT(ECG), and 0.83 for QT(Interpret). The VCG automatic measurement of QT(c) seems to be a better predictor of LQTS than automatic measurement and interpretation of 12-lead ECG.

Prevalence, mutation spectrum, and cardiac phenotype of the Jervell and Lange-Nielsen syndrome in Sweden.

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 ß-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). ß-Blockers reduced, but did not abolish, cardiac events in any previously symptomatic case. ß-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 ß-blocker therapy and compliance, and consideration of ICD implantation in the case of therapy failure is stressed.

Founder mutations characterise the mutation panorama in 200 Swedish index cases referred for Long QT syndrome genetic testing.

BACKGROUND: Long QT syndrome (LQTS) is an inherited arrhythmic disorder characterised by prolongation of the QT interval on ECG, presence of syncope and sudden death. The symptoms in LQTS patients are highly variable, and genotype influences the clinical course. This study aims to report the spectrum of LQTS mutations in a Swedish cohort. METHODS: Between March 2006 and October 2009, two hundred, unrelated index cases were referred to the Department of Clinical Genetics, Umeå University Hospital, Sweden, for LQTS genetic testing. We scanned five of the LQTS-susceptibility genes (KCNQ1, KCNH2, SCN5A, KCNE1, and KCNE2) for mutations by DHPLC and/or sequencing. We applied MLPA to detect large deletions or duplications in the KCNQ1, KCNH2, SCN5A, KCNE1, and KCNE2 genes. Furthermore, the gene RYR2 was screened in 36 selected LQTS genotype-negative patients to detect cases with the clinically overlapping disease catecholaminergic polymorphic ventricular tachycardia (CPVT). RESULTS: In total, a disease-causing mutation was identified in 103 of the 200 (52%) index cases. Of these, altered exon copy numbers in the KCNH2 gene accounted for 2% of the mutations, whereas a RYR2 mutation accounted for 3% of the mutations. The genotype-positive cases stemmed from 64 distinct mutations, of which 28% were novel to this cohort. The majority of the distinct mutations were found in a single case (80%), whereas 20% of the mutations were observed more than once. Two founder mutations, KCNQ1 p.Y111C and KCNQ1 p.R518*, accounted for 25% of the genotype-positive index cases. Genetic cascade screening of 481 relatives to the 103 index cases with an identified mutation revealed 41% mutation carriers who were at risk of cardiac events such as syncope or sudden unexpected death. CONCLUSION: In this cohort of Swedish index cases with suspected LQTS, a disease-causing mutation was identified in 52% of the referred patients. Copy number variations explained 2% of the mutations and 3 of 36 selected cases (8%) harboured a mutation in the RYR2 gene. The mutation panorama is characterised by founder mutations (25%), even so, this cohort increases the amount of known LQTS-associated mutations, as approximately one-third (28%) of the detected mutations were unique.

To Modify or Not to Modify: Allele-Specific Effects of 3'UTR-KCNQ1 Single Nucleotide Polymorphisms on Clinical Phenotype in a Long QT 1 Founder Population Segregating a Dominant-Negative Mutation.

Background There are conflicting reports with regard to the allele-specific gene suppression effects of single nucleotide polymorphisms (SNPs) in the 3'untranslated region (3'UTR) of the KCNQ1 gene in long QT syndrome type 1 (LQT1) populations. Here we assess the allele-specific effects of 3 previously published 3'UTR-KCNQ1's SNPs in a LQT1 founder population segregating a dominant-negative mutation. Methods and Results Bidirectional sequencing of the KCNQ1's 3'UTR was performed in the p.Y111C founder population (n=232, 147 genotype positive), with a minor allele frequency of 0.1 for SNP1 (rs2519184) and 0.6 for linked SNP2 (rs8234) and SNP3 (rs107980). Allelic phase was assessed in trios aided by haplotype data, revealing a high prevalence of derived SNP2/3 in cis with p.Y111C (89%). Allele-specific association analyses, corrected using a relatedness matrix, were performed between 3'UTR-KCNQ1 SNP genotypes and clinical phenotypes. SNP1 in trans was associated with a significantly higher proportion of symptomatic phenotype compared with no derived SNP1 allele in trans (58% versus 32%, corrected P=0.027). SNP2/3 in cis was associated with a significantly lower proportion of symptomatic phenotype compared with no derived SNP2/3 allele in cis (32% versus 69%, corrected P=0.010). Conclusions Allele-specific modifying effects on symptomatic phenotype of 3'UTR-KCNQ1 SNPs rs2519184, rs8234, and rs107980 were seen in a LQT1 founder population segregating a dominant-negative mutation. The high prevalence of suppressive 3'UTR-KCNQ1 SNPs segregating with the founder mutation could contribute to the previously documented low incidence of cardiac events in heterozygous carriers of the p.Y111C KCNQ1 mutation.

[Experiences from a multidisciplinary cardiogenetic clinic]. / Ärftliga hjärt­kärlsjukdomar ­ ett multidisciplinärt arbetssätt krävs.

Comprehensive genetic and clinical care of families with monogenic cardiovascular diseases requires competences from different medical specialties. Genetic assessment, cascade screening, risk estimation, treatment and follow-up is difficult to cover. Fourteen years ago, a center for cardiovascular diseases was created in our hospital, to improve the care of families with monogenic cardiovascular diseases. At our center, clinical geneticists, cardiologists, angiologists, pediatric cardiologists and genetic counselors work together in a seamless organization, while still having different clinic affiliations. A key feature of this organization are the family outpatient clinics, where the proband and his/her relatives at genetic risk are invited to take part. When the family or relatives live in other parts of the country, they are invited to participate through video conference.  In this paper we report our experiences and working routines from more than 300 families and 2000 individuals.

Two automatic QT algorithms compared with manual measurement in identification of long QT syndrome.

BACKGROUND: Long QT syndrome (LQTS) is an inherited disorder that increases the risk of syncope and malignant ventricular arrhythmias, which may result in sudden death. METHODS: We compared manual measurement by 4 observers (QT(manual)) and 3 computerized measurements for QT interval accuracy in the diagnosis of LQTS: 1. QT measured from the vector magnitude calculated from the 3 averaged orthogonal leads X, Y, and Z (QTVCG) and classified using the same predefined QTc cut-points for classification of QT prolongation as in manual measurements; 2. QT measured by a 12-lead electrocardiogram (ECG) program (QTECG) and subsequently classified using the same cut-points as in (1) above; 3. The same QT value as in (2) above, automatically classified by a 12-lead ECG program with thresholds for QT prolongation adjusted for age and sex (QTinterpret). The population consisted of 94 genetically confirmed carriers of KCNQ1 (LQT1) and KCNH2 (LQT2) mutations and a combined control group of 28 genetically confirmed noncarriers and 66 unrelated healthy volunteers. RESULTS: QT(VCG) provided the best combination of sensitivity (89%) and specificity (90%) in diagnosing LQTS, with 0.948 as the area under the receiver operating characteristic curve. The evaluation of QT measurement by the 4 observers revealed a high interreader variability, and only 1 of 4 observers showed acceptable level of agreement in LQTS mutation carrier identification (kappa coefficient >0.75). CONCLUSION: Automatic QT measurement by the Mida1000/CoroNet system (Ortivus AB, Danderyd, Sweden) is an accurate, efficient, and easily applied method for initial screening for LQTS.

The prevalence of prolonged QTc increases by GOLD stage, and is associated with worse survival among subjects with COPD.

BACKGROUND: The role of QTc-prolongation, in relation to the increased mortality in COPD, is unclear. OBJECTIVES: To estimate the prevalence and prognostic impact, assessed as mortality, of QTc-prolongation in COPD, restrictive spirometric pattern (RSP), and normal lung function (NLF), respectively. METHODS: All individuals (n = 993) with COPD and age- and sex-matched non-obstructive referents were identified from well-defined population-based cohorts examined in Northern Sweden in 2002-04. In 2005, the study-sample was invited to re-examination including ECG; QTc was calculated and mortality data collected until 31st December 2010. RESULTS: The prevalence of QTc-prolongation was higher among people with RSP than among those with NLF and, although similar in NLF and COPD, the prevalence increased by COPD-severity. Among participants with COPD, those with QTc prolongation had higher mortality than those with normal QTc, while no such differences were found among participants with NLF or RSP. CONCLUSION: Among participants with COPD, the prevalence of QTc-prolongation increased by disease-severity and was associated with mortality.

Third trimester fetal heart rate predicts phenotype and mutation burden in the type 1 long QT syndrome.

BACKGROUND: Early diagnosis and risk stratification is of clinical importance in the long QT syndrome (LQTS), however, little genotype-specific data are available regarding fetal LQTS. We investigate third trimester fetal heart rate, routinely recorded within public maternal health care, as a possible marker for LQT1 genotype and phenotype. METHODS AND RESULTS: This retrospective study includes 184 fetuses from 2 LQT1 founder populations segregating p.Y111C and p.R518X (74 noncarriers and 110 KCNQ1 mutation carriers, whereof 13 double mutation carriers). Pedigree-based measured genotype analysis revealed significant associations between fetal heart rate, genotype, and phenotype; mean third trimester prelabor fetal heart rates obtained from obstetric records (gestational week 29-41) were lower per added mutation (no mutation, 143±5 beats per minute; single mutation, 134±8 beats per minute; double mutations, 111±6 beats per minute; P<0.0001), and lower in symptomatic versus asymptomatic mutation carriers (122±10 versus 137±9 beats per minute; P<0.0001). Strong correlations between fetal heart rate and neonatal heart rate (r=0.700; P<0.001), and postnatal QTc (r=-0.762; P<0.001) were found. In a multivariable model, fetal genotype explained the majority of variance in fetal heart rate (-10 beats per minute per added mutation; P<1.0×10(-23)). Arrhythmia symptoms and intrauterine ß-blocker exposure each predicted -7 beats per minute, P<0.0001. CONCLUSIONS: In this study including 184 fetuses from 2 LQT1 founder populations, third trimester fetal heart rate discriminated between fetal genotypes and correlated with severity of postnatal cardiac phenotype. This finding strengthens the role of fetal heart rate in the early detection and risk stratification of LQTS, particularly for fetuses with double mutations, at high risk of early life-threatening arrhythmias.

Electrophysiological phenotype in the LQTS mutations Y111C and R518X in the KCNQ1 gene.

Long QT syndrome is the prototypical disorder of ventricular repolarization (VR), and a genotype-phenotype relation is postulated. Furthermore, although increased VR heterogeneity (dispersion) may be important in the arrhythmogenicity in long QT syndrome, this hypothesis has not been evaluated in humans and cannot be tested by conventional electrocardiography. In contrast, vectorcardiography allows assessment of VR heterogeneity and is more sensitive to VR alterations than electrocardiography. Therefore, vectorcardiography was used to compare the electrophysiological phenotypes of two mutations in the LQT1 gene with different in vitro biophysical properties, and with LQT2 mutation carriers and healthy control subjects. We included 99 LQT1 gene mutation carriers (57 Y111C, 42 R518X) and 19 LQT2 gene mutation carriers. Potassium channel function is in vitro most severely impaired in Y111C. The control group consisted of 121 healthy subjects. QRS, QT, and T-peak to T-end (Tp-e) intervals, measures of the QRS vector and T vector and their relationship, and T-loop morphology parameters were compared at rest. Apart from a longer heart rate-corrected QT interval (QT heart rate corrected according to Bazett) in Y111C mutation carriers, there were no significant differences between the two LQT1 mutations. No signs of increased VR heterogeneity were observed among the LQT1 and LQT2 mutation carriers. QT heart rate corrected according to Bazett and Tp-e were longer, and the Tp-e-to-QT ratio greater in LQT2 than in LQT1 and the control group. In conclusion, there was a marked discrepancy between in vitro potassium channel function and in vivo electrophysiological properties in these two LQT1 mutations. Together with previous observations of the relatively low risk for clinical events in Y111C mutation carriers, our results indicate need for cautiousness in predicting in vivo electrophysiological properties and the propensity for clinical events based on in vitro assessment of ion channel function alone.

Instability of repolarization in LQTS mutation carriers compared to healthy control subjects assessed by vectorcardiography.

BACKGROUND: Potassium channel dysfunction in congenital and acquired forms of long QT syndrome types 1 and 2 (LQT1 and LQT2) increases the beat-to-beat variability of the QT interval. OBJECTIVE: To study about the little known variability (instability) of other aspects of ventricular repolarization (VR) in humans by using vectorcardiography. METHODS: Beat-to-beat analysis was performed regarding vectorcardiography derived RR, QRS, and QT intervals, as well as T vector- and T vector loop-based parameters during 1-minute recordings of uninterrupted sinus rhythm at rest in 41 adult LQT1 (n = 31) and LQT2 (n = 10) mutation carriers and 41 age- and sex-matched control subjects. The short-term variability for each parameter, describing the mean orthogonal distance to the line of identity on the Poincaré plot, was calculated. RESULTS: Mutation carriers showed significantly larger (by a factor 2) instability in most VR parameters compared to controls despite higher instantaneous heart rate variability (STVRR) in the control group. The longer the QT interval, the greater was its instability, and the instability of VR dispersion measures. CONCLUSIONS: A greater instability of most aspects of VR already at rest seems to be a salient feature in both LQT1 and LQT2, which might pave the way for early afterdepolarizations and torsades de pointes ventricular tachycardia. In contrast, no signs of increased VR dispersion per se were observed in mutation carriers.

Origin of the Swedish long QT syndrome Y111C/KCNQ1 founder mutation.

BACKGROUND: The Y111C/KCNQ1 mutation causes a dominant-negative effect in vitro but a benign clinical phenotype in a Swedish long QT syndrome population. OBJECTIVE: The purpose of this study was 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. Genealogic investigation was performed for 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 ESTIAGE and DMLE computer software and regional population demographic data. RESULTS: All probands were traced back to a northern river valley region. A founder couple born in 1605/1614 connected 26 of 37 families. Haplotyped probands shared 2-14 (median 10) uncommon alleles, with frequencies ranging between 0.01 and 0.41 (median 0.16) in the controls. The age of the mutation was estimated to 24 generations (95% confidence interval 18; 34), that is, 600 years (95% confidence interval 450; 850) assuming 25 years per generation. The number of now living Swedish Y111C mutation carriers was estimated to approximately 200-400 individuals for the mutation age span 22-24 generations and population growth rates 25%-27%. CONCLUSION: The Y111C/KCNQ1 mutation is a Swedish long QT syndrome founder mutation that was introduced in the northern population approximately 600 years ago. Enrichment of the mutation was enabled by a mild clinical phenotype and strong regional founder effects during population development of the northern inland. The Y111C/KCNQ1 founder population constitutes an important asset for future genetic and clinical studies.

Low incidence of sudden cardiac death in a Swedish Y111C type 1 long-QT syndrome population.

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.