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.

Glucose ingestion causes cardiac repolarization disturbances in type 1 long QT syndrome patients and healthy subjects.

BACKGROUND: Both hypoglycemia and severe hyperglycemia constitute known risk factors for cardiac repolarization changes potentially leading to malignant arrhythmias. Patients with loss of function mutations in KCNQ1 are characterized by long QT syndrome (LQTS) and may be at increased risk for glucose-induced repolarization disturbances. OBJECTIVE: The purpose of this study was to test the hypothesis that KCNQ1 LQTS patients are at particular risk for cardiac repolarization changes during the relative hyperglycemia that occurs after an oral glucose load. METHODS: Fourteen KCNQ1 LQTS patients and 28 control participants matched for gender, body mass index, and age underwent a 3-hour oral 75-g glucose tolerance test with ECGs obtained at 7 time points. Fridericia corrected QT interval (QTcF), Bazett corrected QT interval (QTcB), and the Morphology Combination Score (MCS) were calculated. RESULTS: QTc and MCS increased in both groups. MCS remained elevated until 150 minutes after glucose ingestion, and the maximal change from baseline was larger among KCNQ1 LQTS patients compared with control subjects (0.28 ± 0.27 vs 0.15 ± 0.13; P <.05). CONCLUSION: Relative hyperglycemia induced by ingestion of 75-g glucose caused cardiac repolarization disturbances that were more severe in KCNQ1 LQTS patients compared with control subjects.

Cuidados de enfermería a personas en edad pediátrica con síndrome de QT largo congénito / Nursing care for people in childhood with congenital long QT syndrome", "_i": "

El síndrome de QT largo es una anomalía del sistema eléctrico del corazón caracterizado por prolongación del intervalo QT en el electrocardiograma debido a la alteración en la función de los canales iónicos; ocasiona múltiples mutaciones en los canales de sodio y potasio. Por lo tanto, tiende a desarrollar fibrilación ventricular y Torsade de Pointes poniendo en riesgo la integridad y la vida. El objetivo de la presente revisión bibliográfica es describir el síndrome de QT largo de tipo congénito y subrayar la importancia de ejecutar un plan de cuidados, orientado a la persona en edad pediátrica, de manera que se eviten complicaciones y reincidencias hospitalarias para mejorar su calidad de vida. La valoración de los signos y síntomas por parte del personal de enfermería y todo el equipo de salud, así como la interpretación de los diversos métodos diagnósticos, son fundamentales para brindar una atención de calidad. Aun cuando las manifestaciones son inespecíficas, el diagnóstico eficaz de la enfermedad permite iniciar el manejo apropiado y disminuir la mortalidad infantil.

The long QT syndrome is an anomaly of the electrical system of the heart characterized by prolongation of the QT interval on the electrocardiogram due to an alteration in the function of sodium and potassium ion channels causing multiple mutations in these. Therefore, it tends to develop ventricular fibrillation and helical tachyarrhythmia (Torsades de Pointes), putting at risk the integrity and the life of the child. The objective of this review is to describe congenital long QT syndrome and underline the importance to develop a care plan aimed at the pediatric person in order to avoid complications and hospital recurrence in order to improve their quality of life. Evaluation of signs and symptoms by staff nurses and all health team, as well as the interpretation of the various diagnostic methods, are essential to provide quality care, timely and accurate. Even though the manifestations are no specific, the effective diagnosis of this disease allows starting a proper handling and reducing infant mortality

Prevalence and potential genetic determinants of sensorineural deafness in KCNQ1 homozygosity and compound heterozygosity.

BACKGROUND- Homozygous or compound heterozygous mutations in KCNQ1 cause Jervell and Lange-Nielsen syndrome, a rare, autosomal-recessive form of long-QT syndrome characterized by deafness, marked QT prolongation, and a high risk of sudden death. However, it is not understood why some individuals with mutations on both KCNQ1 alleles present without deafness. In this study, we sought to determine the prevalence and genetic determinants of this phenomenon in a large referral population of patients with long-QT syndrome. METHODS AND RESULTS- A retrospective analysis of all patients with long-QT syndrome evaluated from July 1998 to April 2012 was used to identify those with ≥1 KCNQ1 mutation. Of the 249 KCNQ1-positive patients identified, 15 (6.0%) harbored a rare putative pathogenic mutation on both KCNQ1 alleles. Surprisingly, 11 of these patients (73%) presented without the sensorineural deafness associated with Jervell and Lange-Nielsen syndrome. The degree of QT-interval prolongation and the number of breakthrough cardiac events were similar between patients with and without deafness. Interestingly, truncating mutations were more prevalent in patients with Jervell and Lange-Nielsen syndrome (79%) than in nondeaf patients (36%; P<0.001) derived from this study and those in the literature. CONCLUSIONS- In this study, we provide evidence that the recessive inheritance of a severe long-QT syndrome type 1 phenotype in the absence of an auditory phenotype may represent a more common pattern of long-QT syndrome inheritance than previously anticipated and that these cases should be treated as a higher-risk long-QT syndrome subset similar to their Jervell and Lange-Nielsen syndrome counterparts. Furthermore, mutation type may serve as a genetic determinant of deafness, but not cardiac expressivity, in individuals harboring ≥1 KCNQ1 mutation on each allele.

Combined assessment of sex- and mutation-specific information for risk stratification in type 1 long QT syndrome.

BACKGROUND: Men and women with type 1 long QT syndrome (LQT1) exhibit time-dependent differences in the risk for cardiac events. OBJECTIVE: We hypothesized that sex-specific risk for LQT1 is related to the location and function of the disease-causing mutation in the KCNQ1 gene. METHODS: The risk for life-threatening cardiac events (comprising aborted cardiac arrest [ACA] or sudden cardiac death [SCD]) from birth through age 40 years was assessed among 1051 individuals with LQT1 (450 men and 601 women) by the location and function of the LQT1-causing mutation (prespecified as mutations in the intracellular domains linking the membrane-spanning segments [ie, S2-S3 and S4-S5 cytoplasmic loops] involved in adrenergic channel regulation vs other mutations). RESULTS: Multivariate analysis showed that during childhood (age group: 0-13 years) men had >2-fold (P < .003) increased risk for ACA/SCD than did women, whereas after the onset of adolescence the risk for ACA/SCD was similar between men and women (hazard ratio = 0.89 [P = .64]). The presence of cytoplasmic-loop mutations was associated with a 2.7-fold (P < .001) increased risk for ACA/SCD among women, but it did not affect the risk among men (hazard ratio 1.37; P = .26). Time-dependent syncope was associated with a more pronounced risk-increase among men than among women (hazard ratio 4.73 [P < .001] and 2.43 [P = .02], respectively), whereas a prolonged corrected QT interval (≥ 500 ms) was associated with a higher risk among women than among men. CONCLUSION: Our findings suggest that the combined assessment of clinical and mutation location/functional data can be used to identify sex-specific risk factors for life-threatening events for patients with LQT1.

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.

Factores relacionados con la duración del intervalo QT corregido en pacientes tratados con antipsicóticos / Factors related to the length of the corrected QT interval in patients treated with antipsychotics

Fundamento y objetivo: La duración del intervalo QT corregido (QTc) se ha asociado con un aumento del riesgo de arritmias cardíacas y muerte súbita. Dicha duración se ha relacionado con la edad, la obesidad, el mal control glucémico y el uso de medicamentos, como los antipsicóticos. El objetivo de este estudio naturalístico y transversal ha sido evaluar los factores relacionados con la duración del intervalo QTc en pacientes en tratamiento antipsicótico. Pacientes y método: La duración del intervalo QTc (corregido mediante la fórmula de Bazett) se evaluó en 195 pacientes ­117 varones (60,0%) y 78 mujeres (40,0%)­ con una edad media (desviación estándar) de 28,4 (17,3) años (extremos: 12-84), que recibían tratamiento antipsicótico y estaban ingresados en unidades de hospitalización psiquiátrica. Resultados: La mayor edad (p < 0,001) y el sexo femenino (p = 0,006) fueron los 2 únicos factores asociados con una mayor duración del intervalo QTc. El diagnóstico, el tipo de antipsicótico, la dosis de éste, el consumo de tabaco o los antecedentes de enfermedad cardiovascular no se relacionaron con la duración del intervalo QTc. Solamente un varón con QTc de 455 ms tuvo un intervalo QTc de duración patológica (> 450 ms en varones y > 470 ms en mujeres). Conclusiones: Los factores de riesgo asociados a una mayor duración del intervalo QTc son equivalentes a los hallados en estudios previos con pacientes sin tratamiento antipsicótico

Background and objective: The length of the heart-rate corrected QT interval (QTc) has been associated with an increased risk of cardiac dysrhythmia and sudden death. QTc length has been related to age, obesity, poor glycemic control, and use of drugs, such as antipsychotic medications. The objective of this cross-sectional naturalistic study was to assess the factors associated with QTc length in patients treated with antipsychotics. Patients and method: Bazett's formula for heart-rate correction was used to compute the corrected QT in 195 psychiatric inpatients treated with antipsychotics ­117 males (60.0%), 78 females (40.0%); age (standard deviation): 28.4 (17.3) years (range: 12-84)­. Results: Older age (p < 0.001) and female gender (p = 0.006) were the only factors significantly related to longer QTc interval. Diagnosis, type of antipsychotic, dosage of antipsychotic, tobacco use, and cardiovascular history were not related to QTc length. Only one male patient with QTc = 455 had a pathological QTc length (females > 470 ms, males > 450 ms). Conclusions: Factors related to QTc length in patients treated with antipsychotics are equivalent to those found in previous studies in patients not treated with antipsychotics