However, some of these symptoms, such as swallowing difficulties, falling, or swelling of the legs, are reported more frequently by people with SMA than by those without the disease.
SMA comprises a group of neurodegenerative disorders characterized by the gradual loss of motor neurons — the nerve cells responsible for controlling voluntary muscles — in the spinal cord, leading to muscle weakness and wasting. The disease is normally caused by mutations in the SMN1 gene, which provides instructions for making the SMN protein that is essential for motor neuron survival.
Although the majority of symptoms associated with SMA are motor impairments caused by the loss of motor neurons, recent studies done in people with the most severe forms of SMA revealed that the disorder may also interfere with other systems in the body unrelated to movement control (e.g. heart and sensory nerves).
Moreover, other types of neurodegenerative diseases, such as Parkinson’s disease or amyotrophic lateral sclerosis (ALS), are known to be directly associated with myriad non-motor symptoms (NMS), including some that severely impacts quality of life.
However, in the case of adults with SMA, “a systematic evaluation of the prevalence and significance of non-motor symptoms (…) has not yet been reported,” the researchers wrote.
In the study, these researchers — from the Technische Universität Dresden, in Germany, and their collaborators — set out to investigate if SMA could also be associated with non-motor symptoms that would have a strong negative impact on the quality of life of adults living with the disease.
The team asked a group of 70 adults with SMA type 2 and 3, and 59 age- and sex-matched healthy individuals (controls) to complete a 30-item questionnaire (NMSQuest) normally used to evaluate the burden of non-motor symptoms (e.g. gastrointestinal, neuropsychiatric, and sleep complaints) in people with Parkinson’s and ALS.
In addition, the researchers found that the total non-motor symptom burden was unrelated to disease severity, as measured by the Hammersmith Functional Motor Scale Expanded, the Revised Upper Limb Module, and the Amyotrophic lateral sclerosis functional rating scale-revised.
However, certain questionnaire items, including “swallowing difficulties,” “falling,” or “swelling legs” were reported more frequently in people with SMA than among those who did not have the disease. In contrast, the frequency of neuropsychiatric complaints was similar in both groups.
No significant difference in the total NMSQuest score was found between those who had SMA type 2 and those with type 3, indicating a similar burden of non-motor symptoms among the two groups.
“Taken together, patient-reported prevalence of NMS in adult patients with SMA was generally low, arguing for a low perceived burden of other than the motor system,” the researchers wrote.
“However, ‘swelling legs’ might be a relevant NMS in SMA and its etiology has to be investigated in further studies,” they added. “Further studies including structured interviews and detailed instrument-based measurements of NMS are warranted to unravel the amount of actual and subclinical NMS in adult SMA.”