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Newborn Screening Ontario
Spinal Muscular Atrophy

Spinal Muscular Atrophy

Spinal muscular atrophy is a rare inherited (genetic) disease.  SMA results in muscle weakness and atrophy (muscle wasting).  There are 4 main types of SMA.  The type of SMA depends upon the age of symptom onset and the highest level of motor skills (for example sitting, crawling, walking) that the baby or child is able to achieve:

  • Babies with SMA type 1 are weak and are unable to sit unassisted.  They have symptoms apparent in the first 6 months of life.
  • Children with SMA type 2 can sit by themselves but do not walk.  They have symptoms become apparent from 6-18 months old.
  • Children with SMA type 3 can walk and sit by themselves but start having muscle weakness and wasting (atrophy) in childhood, after 18 months of age.
  • People with SMA type 4 do not have symptoms until adulthood 

SMA affects about 1 in every 10,000 babies born in Ontario.  It is expected that approximately 15 babies with SMA will be identified through newborn screening each year in Ontario.