Using genetic mutations to predict the risk of cardiac arrest

Long QT syndrome is an inherited disorder that can cause rapid heartbeats and seizures. A new study on the genetic mutations behind it offers hopes of preventing sudden death.
Written by Janet Fang, Contributor

Chaotic heartbeats can cause fainting, seizures, and even sudden death.

Long QT syndrome is an inherited disorder that can cause those rapid heartbeats, and a new study has sussed out the genetic mutations behind it. This will help doctors determine who’s at risk for cardiac arrest.

A long QT refers to an abnormal pattern seen on an electrocardiogram, which measures electrical activity in the heart.

For people with the condition, the heart takes a longer time than normal to relax after each contraction – upsetting the careful timing of heartbeats and triggering abnormal rhythms (pictured below).

But patients with only a moderately abnormal long QT pattern don't always develop serious clinical symptoms, and there’s no easy way to predict who’s at risk for sudden death and needs treatment now.

A little science lesson. The nonstop beating of our hearts is sustained by tiny pores on the surface of muscle cells that rhythmically open and close on cue. These pores are ion channels that let electrically charged sodium, calcium, and potassium ions in and out, helping the heart pump blood.

Turns out, the speed at which the potassium channels open indicates the risk for developing the severe heart problems linked to long QT syndrome.

So Coeli Lopes of University of Rochester and colleagues sorted through medical records of 387 patients from families with long QT syndrome.

  1. They found 17 different mutations in potassium channels.
  2. Using frog eggs engineered to express those mutations, they found that mutated channels carried less electrical current and opened more slowly than normal ones (pictured above).
  3. After further checking of medical histories, the researchers found that slow channel opening correlated with episodes of cardiac arrest and sudden death before age 30.
  4. Using a computer model, they found that heart cells carrying the mutant channels are in a relaxed state for longer periods of time. Because of this, they’ve lost the ability to recover from any early beats experienced by the heart, which helps sustain the irregular rates.

"We could link the specific dysfunction to the cardiac risks," Lopes says. Along with factors such as age and gender, she adds, clinicians could use this information to decide whether a patient needs treatment drugs or an implanted defibrillator.

The study was published today in Science Translational Medicine.

Images: normal (top), long QT (bottom) / Science/AAAS

This post was originally published on Smartplanet.com

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