Nearly half of the 24 children with myotonic dystrophy type 1 (DM1) in a French study showed signs of poorer nighttime respiration, reflected by rising carbon dioxide (CO2) levels.

These increases in CO2 did not significantly associate with the presence of sleep apnea — when breathing repeatedly starts and stops during sleep — or with signs of disrupted sleep or a poor performance on lung tests.

Respiratory function and nighttime CO2 levels also remained stable over time in the children.

The findings offer “new and useful insights into disease evolution to better adapt patients’ respiratory follow-up and management,” the researchers wrote, noting a “need for future research to better understand the origins of respiratory and sleep disorders in DM1 patients.”

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Lung function tests favored for people with myotonic dystrophy type 1

The study, “Respiratory function and sleep in children with myotonic dystrophy type 1,” was published in the journal Neuromuscular Disorders.

DM1 is due to mutations in the DMPK gene that cause excessive repeats of a certain segment of DNA. The age of disease onset is informed by the number of these repeats, with congenital and infantile forms linked to more repeats, whereas adult-onset patients tend to have fewer.

As in other types of muscular dystrophy, DM1 patients show progressive muscle weakness and wasting, leading to problems with voluntary movement, as well as dysfunction of the muscles of the heart and those needed for breathing.

Respiratory symptoms have been reported in DM1 patients, although they appear to progress more slowly than in other neuromuscular diseases. Guidelines recommend that DM1 patients undergo early lung function tests to monitor respiratory health.

Sleep-related problems, including nighttime awakenings, excessive daytime sleepiness, and susceptibility to fatigue, are known to affect about 30% of children with DM1, the researchers noted. While it isn’t entirely clear how these symptoms come about, it’s possible that poor breathing at night is a contributing factor.

However, data are lacking on respiratory and sleep problems — and their treatment — among children with DM1, with most sleep disorder studies focused on adult patients, the scientists added.

Researchers with Sorbonne University evaluated these symptoms in 24 children with DM1, who were seen at a hospital in Paris between January 2009 and December 2020.

The children, all white, had a median age of 9.9. Medical records were examined over a median follow-up of 3.75 years.

A total of 86 lung function tests were conducted on 21 patients. Based on available data, three children (12%) showed evidence of restrictive breathing patterns, marked by an inability to fully fill the lungs with oxygen.

Lung function was generally stable over the course of follow-up, which “may suggest a slow decrease in respiratory function” similar to that observed in adult patients, the researchers wrote.

Sleep apnea found in 10 children and was severe in two of them

Nine children complained of symptoms related to disordered breathing during sleep, including daytime sleepiness, fatigue, snoring, or waking up during the night.

Nocturnal gas exchange tests, which look at person’s oxygen and CO2 levels during sleep, were conducted on all children.

Nearly half of children (45%) exhibited signs of alveolar hypoventilation, or insufficient breathing leading to increased CO2 in the bloodstream (hypercapnia).

C02 levels didn’t generally differ between patients with reported sleep-disordered breathing symptoms and those without them, suggesting that the symptoms may not be specific to respiration, the researchers noted.

Gas exchange findings remained relatively stable over the course of follow-up.

Ten children underwent polysomnography, also called a sleep study. This test can record brain waves during sleep, as well as oxygen levels, heart rate, breathing and bodily movements.

Among the seven with brain wave recordings, sleep architecture appeared normal.

All 10 children were found to have sleep apnea, which was mild in two children, moderate in six, and severe in two. Most cases of apnea were obstructive, meaning it was caused by muscles in the airways becoming too relaxed, resulting in a narrowing of the throat.

Overall, lung function and apnea did not correlate with CO2 in the bloodstream, suggesting that hypercapnia is usually asymptomatic, the researchers noted.

Non-invasive ventilation (NIV) to provide nighttime breathing support through a mask was indicated for nine children. Among them, seven patients did not accept or stopped this treatment.

In five children with pre- and post-NIV treatment measurements, C02 levels went down with its use.

While this study was limited by its small number of patients, its findings support future work into developing a clinical scoring system to “guide explorations, define thresholds of hypercapnia and nocturnal alveolar hypoventilation specific to DM1 patients,” the researchers concluded.

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