I have spinal muscular atrophy 3, is there anything that causes sxs to progress after long periods of being stable and do all 3s loose ability to wal?

Disease course: In SMA type III, the later the onset of symptoms, the better the long-term prognosis. Individuals may be prone to respiratory infections but with care may have a normal lifespan. Keep up with your team of specialists including neurologist (neuromuscular focus), pulmonologist, PT, nutritionist, & orthopedist. http://www.ninds.nih.gov/disorders/sma/sma.htm