Clinical Variability in Spinal Muscular Atrophy Type III

Area of Science:

• Neurology
• Clinical Research
• Genetics

Background:

• Spinal muscular atrophy (SMA) type III is a neuromuscular disorder characterized by progressive muscle weakness.
• Understanding the natural history of SMA type III is crucial for assessing treatment efficacy.

Purpose of the Study:

• To analyze the natural history of SMA type III using longitudinal data.
• To establish the annual progression rate of motor function based on the Hammersmith Functional Motor Scale Expanded (HFMSE).
• To identify factors influencing SMA type III progression, including age of onset, SMN2 copy number, and functional status.

Main Methods:

• Longitudinal assessment of 199 SMA type III patients using the HFMSE.
• Application of piecewise linear mixed-effects models to analyze HFMSE changes.
• Inclusion of 375 12-month assessments from 123 patients for descriptive analysis.

Main Results:

• A significant decline in HFMSE scores was observed after age 7 years for both SMA IIIA and IIIB subtypes.
• Motor function increase before age 7 was significant only for SMA IIIA.
• Age, SMA type, and ambulatory status were significantly associated with HFMSE score changes, while gender and SMN2 copy number were not.

Conclusions:

• The study provides critical natural history data for SMA type III, highlighting a significant progression point at age 7.
• Findings will aid in interpreting real-world data from patients treated with available SMA therapies.
• This research contributes to a better understanding of SMA type III progression patterns.