Adult patients with Friedreich’s ataxia have generalized abnormalities in the structure and function of both left and right ventricles of the heart, a study shows.
The study, “Differences in the determinants of right ventricular and regional left ventricular long-axis dysfunction in Friedreich ataxia,” was published in the journal PLOS One.
Friedreich’s ataxia is a neurodegenerative disorder caused by genetic mutations in the FXN gene and consequent deficient levels of frataxin protein. In these patients, the number of repeats of GAA (building blocks of DNA) is increased in the FXN gene copies.
Although the role of frataxin is not fully understood, reduced levels of this protein can promote damage to the nerves that innervate the heart and induce changes in cardiac muscle, leading to heart disease.
About 75 percent of people with Friedreich’s ataxia have cardiac abnormalities. In some patients, the changes are very mild and almost unnoticeable, but in others, the symptoms can be very severe and life-threatening. Heart failure is a leading cause of death among these patients.
Previous studies have shown that changes in the structure of the heart’s left ventricle are an early sign of Friedreich’s ataxia progression.
Subsequently, researchers at the Monash Cardiovascular Research Centre at Monash University, in Australia, investigated the effects of Friedreich’s ataxia on the function of both the left and right ventricles of the heart.
The study enrolled 78 adults with genetically confirmed Friedreich’s ataxia and 54 age-matched healthy volunteers. The team used the non-invasive tissue Doppler imaging method to analyze the heart structures as well as their activity between heartbeats.
Patients were found to have an increased heart rate when compared with controls. They also had smaller left ventricles but with thicker walls. Still, the ejection fraction (the amount of blood pumped out with each contraction of the left ventricle) was similar in the two groups.
All left ventricle measurements were generally larger in male than in female patients.
Further analysis revealed that the contraction velocity of the left and right ventricle muscle walls were lower in individuals with Friedreich’s ataxia.
Contraction velocity of the right ventricle was found to be inversely correlated with the number of GAA repeats in the shorter copy of the FXN gene, meaning that more repeats correlated with a lower contraction velocity. In contrast, the contraction velocity of some of the left ventricle walls was inversely correlated with the number of GAA repeats in the longer copy of FXN.
Increased left ventricle septal wall thickness was the most consistent structural change that was associated with lower contraction velocity.
“There were structural left ventricle changes evident in the Friedrich ataxia subjects in this study . . . which are characteristic of the disease process,” the researchers wrote. However, there was “only minimal evidence of a relationship of GAA repeats” with these changes.
While the team detected generalized abnormalities in function of the right and left ventricles in these patients, additional studies are warranted to explain the regional differences between them.