Type 1 SMA is the most severe, affecting children under the age of 2. Diagnosis of type 1 SMA is usually made in the first 6 months of life. Babies with type 1 SMA are never able to attain normal motor development accomplishments such as sucking swallowing, rolling over, sitting, and crawling. Children with SMA type 1 tend to die before the age of 2, usually due to associated breathing problems.
Babies with SMA type 1 tend to be limp, motionless and even floppy. Their tounges move in a worm-like fashion and they cannot hold their head up when placed in a sitting position. They may have noticeable deformities such as scoliosis, and will have muscle weakness, particularly in the proximal muscles which are located close to the spine. 1, 2