Spinal muscular atrophy

Spinal muscular atrophy (SMA) is a condition that progressively affects messages being passed from the the brain to the muscles. These messages are normally passed along using nerves called motor neurons, which are essential in helping us to sit up, crawl, and walk. In serious cases, a person will not be able to sit up independently and their breathing and swallowing may also be impaired. In the mildest cases, symptoms begin in adulthood and make independent movement such as walking more difficult, but still possible.

There are five main subtypes of spinal muscular atrophy, which are classified by the age at which symptoms of weakness begin. How serious the condition will be cannot be determined by the gene variation. However, members of the same family tend to be affected in a similar way. The most common type is called SMA1 which typically presents in the first few months of life.

Quick facts about spinal muscular atrophy
Genes: SMN1
Inheritance: Autosomal Recessive
Alternative Names: SMA, spinal muscular atrophy
Relevant resources for spinal muscular atrophy

A quick genetics rundown

As humans we have about 23,000 genes. These genes are like tiny instruction manuals that influence our health, growth and development. We inherit half of our genes from our biological mum and the other half from our biological dad. These genes are lined up on structures called chromosomes. Most of us have 23 pairs of chromosomes. The first 22 pairs are called autosomes and for the most part - these are the same among men and women. The 23rd pair determine our sex - two X chromosomes for a female and one X and one Y chromosome for males.

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How is spinal muscular atrophy inherited?

spinal muscular atrophy is known as an autosomal recessive condition. For autosomal recessive conditions, if a person has a variation in one copy of their gene, they are a carrier. This means that they are healthy because they also have a working copy of the gene. But, they can still pass their non-working copy to their child.

If the other parent also happens to be a carrier of the same gene, there is a 25% (1 in 4) chance that they both pass this gene variation on to their child — and as such, have a child affected by the disease.

If both parents are carriers of spinal muscular atrophy, there’s a one in four chance that their children could develop symptoms.
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What is carrier screening?

Carrier testing is like a checkup for your genes. It tests to see if you carry a gene variation that could cause a serious genetic disease in your child. Eugene offers an inclusive genetic carrier screening panel that includes spinal muscular atrophy, but there's a total 301 conditions that can be tested.

Eugene’s carrier test is a clinical grade test that can be done from the comfort of your own home — it’s just a saliva test. You're also paired with a genetic counsellor who provides mindful support and guidance every step of the way.

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Should parents screen for spinal muscular atrophy before or early in pregnancy?

The biggest benefit of screening for spinal muscular atrophy is that it can help future parents understand their reproductive risk so they can be ready and empowered to make more informed decisions. If neither partner are carriers, it provides reassurance and peace of mind that the risk of having a child with a genetic disease is low.

Since 90% of children that have a recessive genetic disease like spinal muscular atrophy had no previous family history of it, it often feels completely out of the blue for the parents. Getting screened is a way to know this risk in advance, which can help familes manage or even prevent the disease in the first place.

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