Reduced MMO is common in SMA types 1-3a and is mainly caused by fatty degeneration of specific mouth opening muscles. Reduced MMO is a sign of bulbar dysfunction in SMA.

Dysphagia in spinal muscular atrophy type II is due to a neurologic dysfunction (lower motor neuron problems from the cranial nerves in the brainstem) influencing the muscle force and efficiency of movement of the tongue and the submental muscle group in combination with a biomechanical component (compensatory head posture). The results suggest an integrated treatment with an adapted posture during meals and the advice of drinking water after meals to prevent aspiration pneumonias.

Reduced mandibular mobility and bite force are common complications in SMA. SMA type and neck muscle strength are important correlates of these complications. We provide further evidence for clinically relevant bulbar involvement in patients with SMA.