People living with SMA type 3 experience greater difficulty breathing and using their hands, arms, and shoulders once they become nonambulant (unable to walk), according to a recent study published in Muscle and Nerve. Previously, researchers have been unclear as to how the condition affects health factors such as lung function and the ability to use one’s upper limbs over time.
Breathing difficulties that come with SMA can lead to complications such as underdeveloped lungs, unproductive coughing, higher risk of viral respiratory infections and pneumonia, aspiration (inhalation of food or drink), and shallow breathing, according to Cure SMA. Difficulties associated with upper-limb functions can limit a person’s independence, as they become more reliant on others for assistance to accomplish tasks such as bathing, eating, and dressing.
For the study, researchers based in the United Kingdom recruited nine boys and 15 girls with SMA type 3 who were nonambulant. The average age of the study participants was 10.5 years old. The study authors followed these participants for two years.
The researchers studied two different health measures. The first was forced vital capacity (FVC), the maximum amount of air a person can breathe out after taking a deep breath in. It measures how well the lungs are working. The second used the Revised Upper Limb Module (RULM), a test that measures how well a person can perform different movements with their hands, arms, and shoulders.
The researchers found that, on average, the children had a 17 percent decrease in lung function over the course of the study. The participants experienced worsening lung function as they grew older and had not been able to walk for longer periods of time. Additionally, lung function decreased more in children who needed to undergo surgery.
RULM scores showed that motor function in the arms decreased over time for nonambulant children with SMA type 3. Older children and those who had been nonambulant for longer periods of time had worse upper body function.
The study authors didn’t find any difference in breathing or upper body function between boys and girls, and they found that how much a child weighed did not impact these health measures over the two-year period.
The researchers noted that none of the study participants had taken newer SMA treatments such as Spinraza. These drugs may help prevent worsening lung or arm function, but more studies are needed in order to know for sure. “This study has shown that [SMA type 3] patients continue to significantly deteriorate in both their respiratory function and upper limb strength following loss of ambulation. Additional studies aimed at assessing the impact of disease-modifying drugs on these outcomes are required,” the authors wrote.
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