Citations

Background: Potentially lethal cardiac channelopathies/cardiomyopathies may underlie a substantial portion of sudden unexplained death in the young (SUDY). The whole-exome molecular autopsy represents the latest approach to postmortem genetic testing for SUDY. However, proper variant adjudication in the setting of SUDY can be challenging. Methods: From January 2012 through December 2013, 25 consecutive cases of SUDY from 1 to 40 years of age (average age at death 27±5.7 years; 13 white, 12 black) from Cook County, Illinois, were referred after a negative (n=16) or equivocal (n=9) conventional autopsy. A whole-exome molecular autopsy with analysis of 99 sudden death-susceptibility genes was performed. The predicted pathogenicity of ultrarare, nonsynonymous variants was determined using the American College of Medical Genetics guidelines. Results: Overall, 27 ultrarare nonsynonymous variants were seen in 16/25 (64%) victims of SUDY. Among black individuals, 9/12 (75%) had an ultrarare nonsynonymous variant compared with 7/13 (54%) white individuals. Of the 27 variants, 10 were considered pathogenic or likely pathogenic in 7/25 (28%) individuals in accordance with the American College of Medical Genetics guidelines. Pathogenic/likely pathogenic variants were identified in 5/16 (31%) of autopsy-negative cases and in 2/6 (33%) victims of SUDY with equivocal findings of cardiomyopathy. Overall, 6 pathogenic/likely pathogenic variants in 4/25 (16%) cases were congruent with the phenotypic findings at autopsy and therefore considered clinically actionable. Conclusions: Whole-exome molecular autopsy with gene-specific surveillance is an effective approach for the detection of potential pathogenic variants in SUDY cases. However, systematic variant adjudication is crucial to ensure accurate and proper care for surviving family members.

Background: Heterologous functional validation studies of putative long-QT syndrome subtype 2–associated variants clarify their pathological potential and identify disease mechanism(s) for most variants studied. The purpose of this study is to clarify the pathological potential for rare nonsynonymous KCNH2 variants seemingly associated with sudden infant death syndrome. Methods: Genetic testing of 292 sudden infant death syndrome cases identified 9 KCNH2 variants: E90K, R181Q, A190T, G294V, R791W, P967L, R1005W, R1047L, and Q1068R. Previous studies show R181Q-, P967L-, and R1047L-Kv11.1 channels function similar to wild-type Kv11.1 channels, whereas Q1068R-Kv11.1 channels accelerate inactivation gating. We studied the biochemical and biophysical properties for E90K-, G294V-, R791W-, and R1005W-Kv11.1 channels expressed in human embryonic kidney 293 cells; examined the electronic health records of patients who were genotype positive for the sudden infant death syndrome–linked KCNH2 variants; and simulated their functional impact using computational models of the human ventricular action potential. RESULTS: Western blot and voltage-clamping analyses of cells expressing E90K-, G294V-, R791W-, and R1005W-Kv11.1 channels demonstrated these variants express and generate peak Kv11.1 current levels similar to cells expressing wild-type-Kv11.1 channels, but R791W- and R1005W-Kv11.1 channels accelerated deactivation and activation gating, respectively. Electronic health records of patients with the sudden infant death syndrome–linked KCNH2 variants showed that the patients had median heart rate–corrected QT intervals <480 ms and none had been diagnosed with long-QT syndrome or experienced cardiac arrest. Simulating the impact of dysfunctional gating variants predicted that they have little impact on ventricular action potential duration. Conclusions: We conclude that these rare Kv11.1 missense variants are not long-QT syndrome subtype 2–causative variants and therefore do not represent the pathogenic substrate for sudden infant death syndrome in the variant-positive infants.

Background: Long-QT syndrome (LQTS), an inherited cardiac repolarization disorder, is an important cause of fetal and neonatal mortality. Detecting LQTS prenatally is challenging. A fetal heart rate (FHR) less than third percentile for gestational age is specific for LQTS, but the sensitivity is only ≈50%. Left ventricular isovolumetric relaxation time (LVIRT) was evaluated as a potential diagnostic marker for fetal LQTS. Methods and Results: LV isovolumetric contraction time, LV ejection time, LVIRT, cycle length, and FHR were measured using pulsed Doppler waveforms in fetuses. Time intervals were expressed as percentages of cycle length, and the LV myocardial performance index was calculated. Single measurements were stratified by gestational age and compared between LQTS fetuses and controls. Receiver-operator curves were performed for FHR and normalized LVIRT (N-LVIRT). A linear mixed-effect model including multiple measurements was used to analyze trends in FHR, N-LVIRT, and LV myocardial performance index. There were 33 LQTS fetuses and 469 controls included. In LQTS fetuses, the LVIRT was prolonged in all gestational age groups ( P <0.001), as was the N-LVIRT. The best cutoff to diagnose LQTS was N-LVIRT ≥11.3 at ≤20 weeks (92% sensitivity, 70% specificity). Simultaneous analysis of N-LVIRT and FHR improved the sensitivity and specificity for LQTS (area under the curve=0.96; 95% confidence interval, 0.82–1.00 at 21–30 weeks). N-LVIRT, LV myocardial performance index, and FHR trends differed significantly between LQTS fetuses and controls through gestation. Conclusions: The LVIRT is prolonged in LQTS fetuses. Findings of a prolonged N-LVIRT and sinus bradycardia can improve the prenatal detection of fetal LQTS.

ABSTRACT Reduced levels of the cardiac human (h)ERG ion channel protein and the corresponding repolarizing current IKr can cause arrhythmia and sudden cardiac death, but the underlying cellular mechanisms controlling hERG surface expression are not well understood. Here, we identified TRIOBP-1, an F-actin-binding protein previously associated with actin polymerization, as a putative hERG-interacting protein in a yeast-two hybrid screen of a cardiac library. We corroborated this interaction by performing Förster resonance energy transfer (FRET) in HEK293 cells and co-immunoprecipitation in HEK293 cells and native cardiac tissue. TRIOBP-1 overexpression reduced hERG surface expression and current density, whereas reducing TRIOBP-1 expression via shRNA knockdown resulted in increased hERG protein levels. Immunolabeling in rat cardiomyocytes showed that native TRIOBP-1 colocalized predominantly with myosin-binding protein C and secondarily with rat ERG. In human stem cell-derived cardiomyocytes, TRIOBP-1 overexpression caused intracellular co-sequestration of hERG signal, reduced native IKr and disrupted action potential repolarization. Ca2+ currents were also somewhat reduced and cell capacitance was increased. These findings establish that TRIOBP-1 interacts directly with hERG and can affect protein levels, IKr magnitude and cardiac membrane excitability.