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HOW IS SMA

INHERITED?

Unlike many other rare neuromuscular diseases, there is a clear understanding of the specific genetic cause of spinal muscular atrophy (SMA).

The characters shown are real patients and the required consent to use their stories has been obtained from the patients and families. Photographs are for illustrative purposes only.

SPINAL MUSCULAR ATROPHY IS AN INHERITED DISEASE

Spinal muscular atrophy (SMA) is an autosomal recessive disease, which means that to be at risk, for a child must inherit one mutated SMN1 gene from each parent. If a child inherits only one mutated SMN1 gene, they are considered a “carrier”, but usually do not have symptoms of spinal muscular atrophy.1

A FAMILY HISTORY

If you have a family history of spinal muscular atrophy, your chances of being a carrier are greater than average. In making reproductive decisions, it may be helpful to consult with your physician to learn what mutation(s) are common in your family.

If two carriers of a mutated SMN1 gene have a child there is a:1

Once your family mutation(s) are known, an appropriate test for your situation may be determined:

If your family mutation(s) are SMN1 deletions, then copy number testing may be appropriate for you.

If your family mutation(s) include a more subtle change in the gene, then your physician and the laboratory may decide whether testing can be done to look for that specific change.

If you are unable to obtain your family mutation(s) information, you can still have a copy number test performed. Your chance of being a carrier (before you have testing) will be calculated from your family history. If your results are normal, your chance of being a carrier may be lower.

ROLE OF A GENETIC COUNSELLOR

Many laboratories and hospitals offer carrier screening to determine whether one or both parents are carriers of the mutated SMN1 gene. This can provide individuals and families with information about the risk of giving birth to a child with spinal muscular atrophy.2

A genetic medical counsellor is trained to make information about genetic risks, testing, and diagnosis easier for families to understand. 

You can read more about the role of a genetic medical counsellor here

When spinal muscular atrophy (SMA) is suspected it is important to have the initial diagnosis confirmed through genetic testing.3

Diagnosing and Testing

References

1. National Organization for Rare Disorders. Spinal Muscular Atrophy. [online] 2012 [cited 2020 Sep 22]. Available from: URL: https://rarediseases.org/rare-diseases/spinal-muscular-atrophy/

2. Quest Diagnostics. SMA Carrier Screen. [online] 2013 [cited 2020 Sep 22] Available from: URL: https://testdirectory.questdiagnostics.com/test/test-detail/16869/sma-diagnostic-test?p=r&q=spinal%20muscular%20atrophy&cc=MASTER.

3. Mercuri E, et al. Diagnosis and management of spinal muscular atrophy: Part 1: Recommendations for diagnosis, rehabilitation, orthopedic and nutritional care. Neuromuscul Disord 2018;28(2):103-115.