Natural History of Mandibular Function in Spinal Muscular Atrophy Types 2 and 3.

Area of Science:

• Neurology
• Genetics
• Clinical Medicine

Background:

• Spinal muscular atrophy (SMA) is a genetic neuromuscular disorder affecting motor neurons.
• Bulbar dysfunction, impacting functions like swallowing and speech, is common in SMA patients.
• The progression of bulbar dysfunction, particularly mouth opening, in SMA types 2 and 3 is not well understood.

Purpose of the Study:

• To prospectively investigate the longitudinal changes in bulbar dysfunction in patients with SMA types 2 and 3.
• To assess the progression of mandibular function and mouth opening over a four-year period in untreated SMA patients.

Main Methods:

• A longitudinal observational study included 44 patients with SMA types 2 and 3.
• Participants underwent assessments including the Mandibular Function Impairment Questionnaire (MFIQ) and clinical examination of masticatory performance, bite force, and mandibular movements.
• Active maximal mouth opening was measured at baseline and after approximately four years.

Main Results:

• Patients with SMA type 2 showed significantly increased MFIQ scores and decreased mandibular movements (p < 0.001).
• Active maximal mouth opening reduced by a mean of 3.5 mm in SMA type 2 patients (p < 0.001), with SMA type 2 being an independent predictor of this decline.
• No significant changes in masticatory performance or maximum voluntary bite force were observed. SMA type 3 patients did not exhibit significant changes in these parameters.

Conclusions:

• Bulbar functions, including mandibular mobility and active maximal mouth opening, significantly decrease over four years in patients with SMA type 2.
• These findings highlight the progressive nature of bulbar dysfunction in SMA type 2 and underscore the need for monitoring and management strategies.