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.

Autonomic Function and QT Interval During Night-Time Sleep in Infant Long QT Syndrome.

BACKGROUND: Sudden infant death syndrome mainly occurs during night-time sleep. Approximately 10% of cases are thought to involve infants with long QT syndrome (LQTS). Autonomic function and QT interval in night-time sleep in early infancy in LQTS infants, however, remain controversial.Methods and Results:Holter electrocardiography was performed in 11 LQTS infants before medication in early infancy, and in 11 age-matched control infants. Control infants were re-evaluated in late infancy. The power spectral density was calculated and parasympathetic activity and sympathovagal balance were obtained. Electrocardiograms of a representative hour during night-time sleep, daytime sleep, and daytime activity, were chosen and QT/RR intervals were manually measured. LQTS infants had significantly lower parasympathetic activity and higher sympathovagal balance during night-time sleep than control infants in early infancy. These autonomic conditions in early infancy were significantly depressed compared with late infancy. Corrected QT interval (QTc) during night-time sleep (490±20 ms) was significantly longer than that in daytime sleep (477±21 ms, P=0.04) or daytime activity (458±18 ms, P=0.003) in LQTS infants, and significantly longer than that during night-time sleep in controls. CONCLUSIONS: A combination of the longest QTc and autonomic imbalance during night-time sleep in early infancy may be responsible for development of life-threatening arrhythmia in LQTS infants. Critical cases should be included in future studies.

Probability of diagnosing long QT syndrome in children and adolescents according to the criteria of the HRS/EHRA/APHRS expert consensus statement.

AIMS: The present study aimed to determine the probability of diagnosing long QT syndrome (LQTS) in children and adolescents based on the HRS/EHRA/APHRS criteria for LQTS. We used data of a school-based electrocardiographic screening programme in Japan. METHODS AND RESULTS: The total numbers of subjects who participated in the screening programme between 2008 and 2013 in Kagoshima, Japan, were 33 051 first- and 34 751 seventh-grade students, aged 6 and 12 years, respectively. The screening process consisted of three steps of examination: the first screening, and the second and third examinations. Among the total subjects, 32 982 first graders (99.8% of the total) and 34 572 seventh graders (99.5% of the total) participated in the first screening. After the first, second, and third screening or examinations, the programme determined 10 first and 32 seventh graders as having a high probability of LQTS according to the HRS/EHRA/APHRS criteria for LQTS. The probability of diagnosing LQTS by the screening programme was 1:3298 (0.30/1000) and 1:1080 (0.93/1000) in first and seventh graders, respectively. During the study periods, three subjects of 7th graders were already diagnosed as having LQTS at the first grade. Therefore, the overall probability of diagnosing LQTS was 1:3298 (95% confidence interval, 1:2036 to 1:8673) and 1:988 (95% confidence interval, 1:742 to 1:1477) in first and seventh graders, respectively. CONCLUSION: This study shows important data on the probability of diagnosing LQTS as ∼1:3300 in subjects aged 6 years and 1:1000 in those aged 12 years based on the HRS/EHRA/APHRS criteria.

Genetic characteristics of children and adolescents with long-QT syndrome diagnosed by school-based electrocardiographic screening programs.

BACKGROUND: A school-based electrocardiographic screening program has been developed in Japan. However, few data are available on the genetic characteristics of pediatric patients with long-QT syndrome who were diagnosed by this program. METHODS AND RESULTS: A total of 117 unrelated probands aged ≤18 years were the subjects who were referred to our centers for genetic testing. Of these, 69 subjects diagnosed by the program formed the screened group. A total of 48 subjects were included in the clinical group and were diagnosed with long-QT syndrome-related symptoms, familial study, or by chance. Mutations were classified as radical, of high probability of pathogenicity, or of uncertain significance. Two subjects in the clinical group died. Genotypes were identified in 50 (72%) and 23 (48%) of subjects in the screened and clinical groups, respectively. Of the KCNQ1 or KCNH2 mutations, 31 of 33 (94%) in the screened group and 15 of 16 (94%) in the clinical group were radical and of high probability of pathogenicity. Prevalence of symptoms before (9/69 versus 31/48; P<0.0001) and after (12/69 versus 17/48; P=0.03) diagnosis was significantly lower in the screened group when compared with that in the clinical group although the QTc values, family history of long-QT syndrome, sudden death, and follow-up periods were not different between the groups. CONCLUSIONS: These data suggest that the screening program may be effective for early diagnosis of long-QT syndrome that may allow intervention before symptoms. In addition, screened patients should have follow-up equivalent to clinically identified patients.

Risk factors for symptoms in long QT syndrome patients in a single pediatric center.

BACKGROUND: Long QT syndrome (LQTS) is a leading cause of sudden cardiac death due to arrhythmia in the pediatric population. This study aimed to determine risk factors for the presence of LQTS-related symptoms in a single pediatric center. METHODS: Subjects were 146 consecutive LQTS patients (M:F = 72:74) who visited our hospital between April 2005 and August 2012 and during the preceding 24 months. A total of 103 subjects were discovered by the school-based screening, 15 subjects visited because of their symptoms, and the others were 28 subjects. One subject died. RESULTS: Risk factors for the presence of symptoms after diagnosis were longer QTc values (P = 0.01), the presence of history of LQTS-related symptoms (P = 0.04), and longer follow-up periods (P = 0.03). Non-compliance with medicine was the sole risk factor for frequent symptoms after diagnosis (P = 0.02). In subjects discovered by the school-based screening, nine subjects (9%) had LQTS-related symptoms after diagnosis. Longer follow-up periods were the sole risk for the presence of symptoms (P = 0.04). The mean period until the presence of symptoms after diagnosis was 3.1 ± 2.7 years (0.1-7.1 years). CONCLUSION: Good compliance with medicine is essential to prevent recurrent episodes. A new strategy is required to prevent subjects, including school-based screened subjects, from dropping out of hospital visits.