Heart medications may ease symptoms of muscular dystrophy

A type of heart drug called a calcium channel blocker successfully eased myotonic dystrophy type 1 symptoms in lab mice bred to have the genetic problem that causes that form of muscular dystrophy, according to a recent study. Photo by Adobe Stock/HealthDay News

A regularly prescribed class of heart medications might be capable of treating one of the most common forms of muscular dystrophy, a new study in mice suggests.

Myotonic dystrophy type 1 (DM1) is caused by abnormal RNA that affects the function of calcium channel receptors, which help convert impulses from nerve cells into chemical signals that guide muscle movement, the researchers explained.

Given that, a type of heart drug called a calcium channel blocker might be able to eliminate the “noise” caused by this abnormal RNA, they reasoned.

These drugs successfully eased DM1 symptoms in lab mice bred to have the genetic problem that causes that form of muscular dystrophy, according to results published Tuesday in the Journal of Clinical Investigation.

“We think that the calcium channel is a new therapeutic target and if we can target it correctly, pharmacologically that it will improve muscle function and health,” the researchers wrote.

People with DM1 suffer from muscle weakness and prolonged muscle tension, which makes it difficult to relax muscles after use, they said in background notes.

Muscle problems caused by the disease affect the eyes, heart and brain, eventually leading to problems walking, swallowing and breathing.

More than two decades ago, co-researcher Dr. Charles Thornton — a neurologist at the University of Rochester Medical Center — discovered how a genetic flaw causes DM1.

A genetic “stutter” results in thousands of repetitions of code on a segment of chromosome 19, Thornton’s earlier research found.

In turn, that defect causes an accumulation of the abnormal RNA that interferes with healthy muscle function.

To investigate this cycle and better understand DM1, researchers bred lab mice that had four of the gene defects found in DM1 — specifically, in genes associated with the calcium and chloride channels.

“Myotonic dystrophy is a really complicated disorder, which you can think of as almost like an aggregate of many diseases,” co-researcher John Lueck, an associate professor with the University of Rochester Medical Center, said in a university news release.

They then tried to treat these mice with calcium channel blockers normally used to treat high blood pressure, heart rhythm problems and migraines.

Verapamil, a calcium channel blocker used to treat blood pressure and chest pains, caused the mice to quickly recover muscle function and appear as healthy as normal lab mice, the researchers reported.

“Our research also suggests that muscle impairment in DM1 is potentially mitigated by common clinically available calcium channel blockers, and that calcium channel modulation is a potential therapeutic strategy,” Lueck said.

However, researchers noted that verapamil shouldn’t be considered for use in humans with DM1, since it can have harmful side effects. Also, research in mice doesn’t always pan out in humans.

“Our goal now is to find the appropriate and safe calcium channel blocker that will do the job, and we believe it exists,” the researchers concluded.