Short QT syndrome review

From diagnostic testing to precision medicine: the evolving role of genomics in cardiac channelopathies and cardiomyopathies in children

Pediatric sudden cardiac death (SCD) is the sudden unexpected death of a child or adolescent due to a presumed cardiac etiology. Heritable causes of pediatric SCD are predominantly cardiomyopathies and cardiac ion channelopathies. This review illustrates recent advances in determining the genetic cause of established and emerging channelopathies and cardiomyopathies, and how broader genomic sequencing is uncovering complex interactions between genetic architecture and disease manifestation. We discuss innovative models and experimental platforms for resolving the variant of uncertain significance as both the variants and genes associated with disease continue to evolve. Finally, we highlight the growing problem of incidentally identified variants in cardiovascular disease-causing genes and review innovative methods to determining whether these variants may ultimately result in penetrant disease. Overall, we seek to illustrate both the promise and inherent challenges in bridging the traditional role for genetics in diagnosing cardiomyopathies and channelopathies to one of true risk-predictive precision medicine.

Association of MEF2A gene polymorphisms with coronary artery disease

Background:

Coronary Artery Disease (CAD) is the most common cause of death worldwide. MEF2A directly regulates target genes in the process of muscle development. This gene product is a transcription factor. MEF2A protein in homodimer or heterodimer forms binds to A/T-rich cis elements with conserved sequence in promoter, regulator, and enhancer of many genes, which are determining in evolution and development of skeletal, heart, and smooth muscle cells, especially endothelial cells. In fact, this protein maximizes the activity of these elements.

Objectives:

The two MEF2A gene polymorphisms that were proposed to have an association with CAD are rs34851361 (A/G) and rs325400 (T/G) SNPs. This study aimed to examine these associations.

Patients and Methods:

This study was a molecular case-control study. Blood samples were collected from 300 patients with CAD and 150 healthy people from Golestan and Imam Khomeini Hospitals, Ahvaz, Iran. In both groups, angiography had confirmed the presence or lack of stenosis. Association of rs34851361 and rs325400 with CAD was evaluated by PCR and then restriction fragment length polymorphism (RFLP) analysis was performed.

Results:

Chi square test showed no association between rs34851361 SNP and CAD (χ² = 3.59, df = 2, and P = 0.16); however, there was an association between rs325400 SNP and CAD (χ² = 24.77, df = 2, and P < 0.001). A/T haplotype showed association with CAD and G/G and G/T showed protective effect against CAD.

Conclusions:

The results of this study show that rs325400 polymorphism is in association with CAD; meanwhile, none of the rs34851361 genotypes was associated with CAD.

Exercise-related QT interval shortening with a peaked T wave in a healthy boy with a family history of sudden cardiac death

An asymptomatic 15-year-old boy, who had a family history of sudden cardiac death, was referred for screening for cardiac disease. The 12-lead electrocardiogram at rest showed a short QT/QTc(Bazett)/QTc(Fredericia) interval of 320/388/364 ms, but the intervals were further shortened to 200/339/284 ms after the treadmill test concomitant with appearance of a peaked T wave. Other conventional cardiac examinations were normal, but effective refractory period was less than 180 ms in both ventricles, and double ventricular extrastimulation reproducibly induced nonsustained polymorphic ventricular tachycardia. Intravenous administration of epinephrine also induced a short QT interval and a peaked T wave, and a hump was manifested on the T wave of the first postpacing beat with a longer preceding R-R interval. Furthermore, a couple of premature ventricular complexes originated from a similar timing as the hump. Genetic analysis did not show the mutation in KCNQ1, KCNH2, KCNE1, KCNE2, KCNJ2, SCN5A genes but revealed single nucleotide polymorphism (C5457T) in SCN5A gene.