Oral function tests such as maximum tongue pressure and maximum mouth opening can effectively discriminate between various types of spinal muscular atrophy (SMA) and between ambulatory and nonambulatory individuals, according to a new study published in the Orphanet Journal of Rare Diseases.

The study highlighted that oral function tests could supplement existing motor scores on specific questions about bulbar functioning or in certain subgroups such as critically affected nonambulatory individuals.

The researchers analyzed oral function test data from 43 adults with genetically confirmed 5q-SMA. Differences in oral function among individuals with different SMA types and numbers of SMN2 copies were evaluated.

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In addition, spearman’s rho correlations among absolute maximum measures of oral function, including maximum bite force and endurance, maximum tongue pressure and endurance, and maximum mouth opening were analyzed among themselves and with established clinical outcome scales.

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Results revealed that absolute maximum measures of oral function, specifically maximum bite force, maximum tongue pressure, and maximum mouth opening were effectively able to discriminate between patients having different SMA types, patients with a different number of SMN2 copies, and those with varying walking ability.

Among the absolute measures, maximum mouth opening had the highest correlation coefficients, confirming its strong correlation with SMA type, the number of SMN2 copies, maximum bite force, maximum tongue pressure, and all clinical outcome scales. “Our findings support the idea that bulbar involvement is particularly well reflected in the measurement of maximal mouth opening,” the authors highlighted.

Similar results were found for measuring maximum tongue pressure due to its outlined correlations with established motor scores. In addition, all correlations evaluating endurance measures of oral function were found to be weaker and statistically insignificant. “From a clinical perspective, both methods are cost-effective and rather easy to handle for routine use,” the authors added.

Teresa Kruse and colleagues commented that the wide-ranging data on oral function in SMA can reveal additional insights into bulbar involvement through subgroup analyses. However, further research is needed to confirm oral function tests as a standardized outcome measure in the clinical evaluation of SMA patients.

SMA is a rare autosomal recessive neurodegenerative disorder characterized by progressive degeneration of motor neurons in the spinal cord leading to progressive weakness and loss of movement. This weakness and degeneration of bulbar muscles become evident in impaired muscle strength and increased oral function fatigue, affecting patients’ ability to speak, chew, swallow, and open their mouths to the maximum limit. However, compared to the axial and proximal muscles, oral functions are usually less severely affected in patients with SMA type 1 and 2.

In severely affected adults with residual motor function, assessment of oral function can provide valuable information about the declining bulbar function. This becomes especially useful when existing motor function scores are limited due to the patient’s immobility. Including measurements of muscle endurance in oral function assessments can further enhance their effectiveness, despite being considered less reliable than maximum muscle strength measurements.


Kruse T, Shamai S, Leflerovà D, et al. Objective measurement of oral function in adults with spinal muscular atrophy. Orphanet J Rare Dis.  Published online May 3, 2023. doi:10.1186/s13023-023-02688-4