6MWT can identify type 3 SMA patients with neuromuscular junction dysfunction.

Area of Science:

• Neurology
• Clinical Medicine
• Biophysics

Background:

• Spinal muscular atrophy (SMA) type 3 is a neuromuscular disorder affecting ambulation.
• Neuromuscular junction (NMJ) dysfunction contributes to muscle weakness and fatigue in SMA.
• The 6-minute walk test (6MWT) assesses functional mobility and endurance.

Purpose of the Study:

• To investigate the correlation between gait velocity decline during the 6MWT and NMJ dysfunction in SMA type 3 patients.
• To determine if the 6MWT can serve as a surrogate marker for NMJ dysfunction in this population.

Main Methods:

• Fifteen ambulant SMA type 3 patients (aged 9-66 years) underwent the 6MWT and low-rate repetitive nerve stimulation (LR-RNS) testing.
• Gait velocity changes during the 6MWT and % loss in LR-RNS to the axillary nerve were quantified.
• Correlation analysis was performed between 6MWT performance and LR-RNS findings.

Main Results:

• 6MWT distances varied from 66 to 575m, with a 0% to -69% decline in velocity from minute 1 to 6.
• LR-RNS showed a % loss ranging from -31.7% to +4.2%.
• A strong positive correlation (r=0.86) was observed between 6MWT velocity changes and LR-RNS % loss.

Conclusions:

• The 6MWT effectively identifies fatigue in ambulant SMA type 3 patients with concurrent NMJ dysfunction.
• This accessible clinical test can aid in identifying patients who may respond to therapies aimed at improving neuromuscular transmission.
• The findings support the use of the 6MWT as a practical tool for monitoring disease progression and treatment efficacy in SMA type 3.