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Newborn Screening Ontario
Spinal Muscular Atrophy

Health Care Providers

Spinal Muscular Atrophy Overview

Spinal muscular atrophy (SMA) is a rare genetic disease affecting about one in every 10,000 babies.  SMA results in muscle weakness and atrophy.  The 4 main types of SMA are defined by 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 and rarely survive beyond 2 years of age
  • 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

Treatment has recently become available for SMA.  When it is given to asymptomatic babies who have inherited SMA it has been found to be effective in preventing the development of the disease. 

Because of this new treatment, newborn screening for SMA is being offered in Ontario.  Starting in January 2020, the blood collected from the heel prick performed on all Ontario newborns for the Newborn Screen will also be used to screen for SMA.  A baby with screen positive result will have a high risk of having SMA.  Babies confirmed to have SMA after identification through screening can be treated as early as possible, slowing or even preventing the development of the disease. 

This pilot project taking place over the first few months in 2020 is one of the first times that a condition is to be phased-in in this fashion before being formally added to the list of diseases currently screened in Ontario.  One reason this is happening is that the SMA treatment has recently become available.   Screening babies as soon as possible (in the form of a pilot) means that more babies with SMA can be identified and started on treatment now.  As well, phasing in screening allows time to develop regulatory and policy changes required in the province to make it an officially screened disorder.   Despite this being a pilot project, the test offered has been rigorously validated and is highly accurate.

Babies who have their blood taken for dried blood spot screening in Ontario will also be screened for SMA.  Families that decline dried blood spot screening will not be screened for SMA. 

It is expected that approximately 15 babies with SMA will be identified through newborn screening each year in Ontario.  Newborn screening for SMA will detect SMA type 1 and 2, most cases of type 3, and some cases of type 4.  Infants with a screen positive result will be referred for follow up.

Genetics of SMA

SMA is inherited in an autosomal recessive manner.   When a baby is born with no working copies of the SMN1 gene then they will develop SMA.  SMA can be caused by deletions in the SMN1 gene (~97% of cases) or other genetic changes (~3%).  Newborn screening will only detect cases of SMA caused by deletions in the SMN1 gene. 

The type of SMA depends upon the number of copies of another gene, SMN2.  People can have 1 to 6 copies of the SMN2 gene.  The higher number of SMN2 copy numbers, the less severe the symptoms.

The table below gives the chance of having each type of SMA depending upon the SMN2 copy number.  For example, a baby found to have 1 copy of SMN2 has a 96% chance of having SMA type 1 and a 4% chance of having SMA type 2. 

SMA type

SMN2 copy number





SMA type 1





SMA type 2





SMA type 3





*includes both SMA type 3 and type 4

Babies with a deletion of both their copies of SMN1, and with SMN2 copy numbers of 1, 2, 3 or 4 will be reported as having a screen positive result and referred for more testing.  This means that >99% of SMA type 1 and 2 cases and >97% of SMA type 3 cases caused by a deletion in the SMN1 gene will be picked up by screening.  SMA type 4 will also be detected if caused by SMN2 copy numbers of 4 or less.

Screen Positive Results and Follow-up

Newborn Screening Ontario (NSO) refers screen positive babies to specialized follow-up clinics in their region for more testing. NSO refers to these specialized centres as newborn screening Regional Treatment Centres.  The centres include:

  • London Health Sciences Centres, London
  • Hamilton Health Sciences Centre, Hamilton
  • Hospital for Sick Children, Toronto
  • Kingston General Hospital, Kingston
  • Children’s Hospital of Eastern Ontario, Ottawa

Typically babies are referred to their closest centre.  For families that live in more remote locations, they can decide which of the five centres they would prefer to attend.

Health care providers at the Regional Treatment Centres then contact the baby’s doctor, midwife, nurse practitioner, or parents directly to inform them of the results and arrange appointments and tests that are required.  Due to how newborn screening is performed for SMA, the likelihood is very high that screen positive babies will be confirmed to have SMA.  At the baby’s first appointment the specialists, including a pediatric neurologist, will likely discuss treatment and management options.


  • Treatment is available for babies with 3 or less copies of the SMN2 gene.  Babies with 3 or less copies of the SMN2 gene are expected to have SMA types 1, 2 or 3.
  • Babies with 4 or more copies of the SMN2 gene will be checked regularly for symptoms of SMA.  Babies with SMN2 copy numbers of 4 or more are expected to have SMA types 3 or 4, but some babies may develop type 2.  If symptoms develop your baby’s specialist will discuss treatment options.
  • Treatment needs to begin as early as possible for infants with 3 or less copies of the SMN2 gene.  This is why newborn screening for SMA is being offered.  Without treatment the more severe, early onset forms of SMA (in particular SMA type 1) will lead to death in the first year or two of life.
  • In Ontario, Nusinersen is approved for treatment of patients with SMA who have 3 or less copies of the SMN2 gene.
    • Treatment is provided at a medical facility or hospital by a physician.
    • Treatment with Nusinersen is given through a lumbar puncture (spinal tap).
    • Six treatments are required in the first year of life and then 3 times per year for life; Treatment is lifelong.
    • Nusinersen can stop the progression of SMA if started early. 


  • Gene therapy (Zolgensma) is being developed but is not yet approved for use in Canada. It may be available on a compassionate basis through Global Access Program however this cannot be guaranteed.

Request Screening Results

Screen negative results will not be reported.  If you would like request a copy of the results please contact us.