Treatment may ease nighttime breathing issues in adults with SMA

Evrysdi (risdiplam) may improve nighttime breathing in adults with spinal muscular atrophy (SMA), a small, real-world study in Italy found.

After 12 months on Evrysdi, study participants experienced fewer episodes of breathing that stopped or became too shallow during sleep, along with fewer associated drops in blood oxygen levels.

Researchers also detected a change in cardiac autonomic function, the nervous system’s automatic control of heart rate and other aspects of heart function. This change was associated with the reduction in nighttime breathing disturbances, suggesting that fewer respiratory events during sleep may contribute to a healthier autonomic balance.

“In adult patients with SMA, [Evrysdi] therapy may be associated with improvements in nocturnal respiratory function and autonomic activity,” the researchers wrote.

The study, “Sleep disordered breathing and autonomic outcomes in adult patients with spinal muscular atrophy (SMA) receiving Risdiplam,” was published in Sleep Medicine.

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Weak muscles lead to breathing issues

In SMA, deficient levels of survival motor neuron (SMN) protein result in the progressive loss of motor neurons, the nerve cells that control movement. This leads to SMA symptoms such as muscle weakness and wasting, which can affect not only movement but also the muscles needed for breathing.

Sleep-related breathing disturbances have been reported in both children and adults with SMA. These can include obstructive events, in which airflow is physically blocked, as well as nonobstructive events that may result from weakness in the muscles involved in breathing.

Abnormalities in cardiac autonomic function have also been reported in SMA, particularly in children with breathing problems during sleep. However, little is known about the relationship between nighttime breathing disturbances and autonomic activity in adults with SMA.

Evrysdi, sold by Genentech, is an SMA treatment that targets the disease’s underlying cause by helping cells produce a fully functional version of the SMN protein. Studies have shown that Evrysdi can benefit daytime respiratory and motor function, but whether the therapy can improve breathing during sleep or influence autonomic regulation in adults remains largely unexplored.

To investigate, researchers at the University of Palermo in Italy conducted an observational study between January and June of 2024 involving adults with SMA who had not previously received SMA therapy.

The study initially enrolled 22 participants, ages 16 and older. Ten needed noninvasive ventilation; five who started ventilation were excluded because it could affect the study results. Another participant stopped Evrysdi after six months, leaving 16 people with SMA type 2 or 3 — 10 women and six men — who completed the study. Their mean age was 37; 14 could sit but not walk, while two could walk.

Participants received 5 mg of Evrysdi once daily for 12 months. Before starting treatment and again one year later, participants underwent overnight cardiorespiratory monitoring at home to assess breathing during sleep and heart rate variability (HRV, variations in the time between heartbeats that provide information about cardiac autonomic regulation). Lung function, respiratory muscle strength, and motor function were also assessed.

After one year of Evrysdi, nighttime breathing significantly improved. The apnea-hypopnea index (AHI) — the average number of times per hour that breathing stops or becomes abnormally shallow during sleep — decreased from a median of 8.3 events per hour to 3.8.

The number of oxygen drops associated with these events also decreased, from a median of 5 per hour to 3.7. However, overall nighttime blood oxygen levels did not change significantly, which the researchers noted may partly reflect the short amount of time participants spent at abnormally low oxygen levels even before treatment.

In three patients, the severity of sleep-disordered breathing shifted from moderate to mild. Obstructive and nonobstructive events also tended to decrease, but the changes were not statistically significant.

Lung function and respiratory muscle strength also improved. The researchers suggested that better upper-airway muscle function could partly explain the reduction in nighttime breathing disturbances, although this was not directly assessed. Motor function scores showed a trend toward improvement, but the changes did not reach statistical significance.

The researchers examined cardiac autonomic regulation using HRV data available from 13 participants. After treatment, one measure, called the SD2/SD1 ratio, significantly decreased, which the researchers said suggested a reduction in sympathovagal balance (the balance between the two branches of the autonomic nervous system that help regulate heart activity).

The decrease in SD2/SD1 was significantly associated with the reduction in nighttime breathing disturbances: Participants with greater decreases in AHI also tended to show greater decreases in SD2/SD1. This led the researchers to speculate that reducing sleep-related breathing disturbances may have contributed to the observed change in cardiac autonomic regulation.

Overall, the findings suggest Evrysdi “may improve nocturnal respiratory and cardiac autonomic function “in adults with SMA, the researchers concluded, adding that “additional studies are necessary to understand mechanisms by which [Evrysdi] may improve nocturnal respiratory function.”