Arrhythmia Gene Variants Reclassified

Vanderbilt’s SyncroPatch, the robotic patch clamp system used in the study. (Photo by Andrew Glazer)
Arrhythmia Gene Variants Reclassified
Vanderbilt’s SyncroPatch, the robotic patch clamp system used in the study. (Photo by Andrew Glazer)
Innovation in high-throughput testing aids in classifying many “uncertain” mutations.

Vanderbilt University Medical Center researchers have used high-throughput technology to analyze genetic variants associated with the arrhythmia disorder Brugada syndrome, providing essential data related to their function. The findings were published in the American Journal of Human Genetics.

The authors studied the cardiac sodium channel gene SCN5A, in which mutations are the most common recognized cause of Brugada Syndrome. However, of the 1,390 variants reported in the gene, most are considered of “uncertain significance,” the authors wrote. This uncertainty limits how they can be used in clinical care.

“We would like to be able to use genome sequencing to find mutations that put people at risk of disease, in order to prevent disease. But this idea of genetic or precision medicine doesn’t work well when we don’t know the impact of the mutations we find,” said Andrew Glazer, Ph.D., a postdoctoral fellow in the Vanderbilt Center for Arrhythmia Research and Therapeutics and lead author of the study.

A Genetic Black Box

Brugada Syndrome is a cause of sudden cardiac death due to serious ventricular arrhythmia.

The researchers focused on 83 variants in SCN5A. The problem has been that 80 percent of identified SCN5A variants lack functional data, Glazer said. “We’re not sure whether or not they cause disease.”

“This idea of genetic or precision medicine doesn’t work well when we don’t know the impact of the mutations we find.”

New Tech Increases Throughput

An automated robotic patch clamp electrophysiology system enabled the researchers to rapidly test ion channels that contained each of the variants. The tech was made possible by an NIH High-End Instrumentation grant to principal investigator Dave Weaver, Ph.D., scientific director of the High-Throughput Screening Facility at Vanderbilt.

“That system really enabled the science because we could study lots of mutants in lots of replicate cells relatively quickly,” Glazer said.

Ten of the 83 variants had been previously studied and served as controls. Of the remaining variants, the researchers discovered 22 conferred total loss of channel function, and 22 conferred partial loss. Wrote the authors, “Structural modeling identified likely mechanisms for loss of function [for many mutations], including altered thermostability and disruptions to alpha helices, disulfide bonds, or the permeation pore.”

The remaining variants were reclassified as benign, likely benign or likely pathogenic. In total, the team dropped the number of variants on their “uncertain significance” list from 61 to just 12.

 

Putting Results into Practice

The findings could help aid Brugada syndrome diagnoses, said senior author Dan Roden, M.D., Sam L. Clark M.D., Endowed Chair and senior vice president for personalized medicine at Vanderbilt.

“The problem we have is that as more and more people are getting genome sequencing for a variety [of] reasons, we encounter more and more SCN5A variants of uncertain significance. We need studies like this one that help tell us which ones may place patients at risk for serious arrhythmias.”