In SMA type 4 weakness, most commonly develops after 35 years of age (less commonly between 18 to 35 years old). Weakness of proximal muscles is more prominent in the legs than in the arms. Insidious onset and very slow progression are the characteristic features, and life span is normal.
Also indexed as
Adult onset spinal muscular atrophy, Type IVadult onset SMA - [spinal muscular atrophy], Type IVtype 4 SMA - [spinal muscular atrophy]