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SMA is a rare, serious, inherited condition, in which nerves that control muscles (motor neurons) die. This results in muscles becoming weak and wasting away, with eventual loss of movement and difficulty with functions such as breathing, swallowing, feeding and speaking¹

For motor neurons to be able to work properly and survive, the body needs, among other things, a protein called SMN or ‘survival motor neuron’.^1,2 Without SMN protein, motor neurons stop working and die, and muscles become weaker with eventual loss of movement and difficulty with functions such as breathing, swallowing, feeding and speaking³

In unaffected people, the body is able to produce the SMN protein from genes called SMN genes. There are 2 types of SMN gene, SMN1 and SMN2:^1,2,4–6

• Survival motor neuron 1 (SMN1)
  
  The SMN1 gene is the primary gene and produces most of the SMN protein that motor neurons need to work properly^1,4–6
• Survival motor neuron 2 (SMN2)
  
  Although the SMN2 gene also produces SMN protein, it makes several versions of this protein and only small amounts of these work properly (‘functional SMN protein’).^4,6,7 The SMN2 gene therefore acts like a ‘back-up’ to support SMN protein production, but is not able to produce sufficient SMN protein on its own^4,7

In people with SMA, the SMN1 gene is either faulty (mutated) or completely missing.4,5,8 The SMN2 gene cannot produce enough functional SMN protein to make up for the loss of the SMN1 gene.^1,2,4,6 As a result, there is not enough functional SMN protein produced to keep motor neurons healthy and working properly^1,2,5,9

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SMA is a spectrum disease with a range of symptoms that may vary in severity.¹⁻³ There are different types of spinal muscular atrophy ranging from Types 0–4.^1–3 The progression of the types changes depending on the age at onset of symptoms, milestones achieved, and symptoms experienced¹⁻³

There are different symptoms that may occur depending on the type of SMA.^1–2 If you notice any of the symptoms below, do not hesitate to contact your doctor^1–3

SMA Type 0

Age of symptom onset: Birth²

In the most severe form, symptoms usually begin to develop before birth. The child’s movements may slow down during pregnancy⁴

SMA Type 1

Age of symptom onset: ≤6 months^2,5

• Poor head control^1,2,6,7
• Weak legs and arms^1,2,6,7
• Fast belly breathing^1,2,8
• Difficulty feeding/swallowing^1,2
• Weak cry and cough^3,8

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SMA Type 2

Age of symptom onset: 6–18 months^2,5

• Struggles to sit unsupported^1,2,9
• Weak legs and arms^1,2,10
• Can’t roll over^9,10
• Slow/lost physical development^1,2,9,11
• Swallowing and coughing difficulties^1,2
• Shaking hands²

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SMA Type 3

Age of symptom onset: >18 months–teens^2,5

People with this form of SMA may have poor balance, and have problems with standing up and walking/climbing stairs¹²

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SMA Type 4

Age of symptom onset: >18 years²

In the mildest form, symptoms don’t appear until adulthood. People with this form of SMA typically have mild weakness, without breathing difficulties¹²

Yes, as SMA is caused by a faulty (mutated) or missing gene, it is considered a genetic disease and is usually inherited¹

A child inherits 2 copies of each gene, one from their mother and one from their father.² For a child to be born with SMA, they must inherit a faulty gene from both their mother and their father¹

If either copy of the gene (from the mother or from the father) is faulty, the other parent’s unaffected gene can make sure enough SMN protein is produced for the motor neurons to work properly.^1,2 People who have one unaffected copy of the SMN1 gene and one faulty copy are known as ‘carriers’ and typically do not show any symptoms.¹ Most carriers have no idea they carry the faulty gene until they have a child born with SMA³

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SMA is a recessive disorder which typically occurs if a child inherits 2 copies of the faulty or missing survival motor neuron 1 (SMN1) gene, one from their mother and one from their father.¹⁻³ This type of inheritance pattern is referred to as ‘recessive’, and means that, generally, both parents must be carriers for a 25% chance the disease will be inherited³

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In general, carriers do not experience symptoms of SMA.¹ Most carriers are unaware they have the missing or faulty gene until they have a child with spinal muscular atrophy²

SMA is a rare disease, affecting around 1 in 10,000 newborns, and can impact any race or sex.¹⁻⁴ Around 1 in 50 people are carriers of SMA, although this will vary slightly depending on your geographical location^1,5

SMA typically affects males and females equally, this is due to the way that the disease is inherited by the child from their parents^1,2

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There are signs of SMA which are important to look out for, although the signs change depending on the age^1,2

For babies at birth:^2,3

• In the most severe form, symptoms usually begin to develop before birth.
  The child’s movements may slow down during pregnancy³

For babies aged 0–6 months:^2,4

• Poor head control^1,2,5−7
• Weak legs/arms^1,2,5–7
• Weak cry and cough^1,2,8
• Difficulty feeding/swallowing^1,2,7
• Fast belly breathing^1,2,8

For babies aged 6–18 months:^2,4

• Weak legs and arms^1,2,9,10
• Struggles to sit unsupported^1,2,9,11
• Can’t roll over^9–11
• Slow/lost physical development^1,2,9,11,12
• Swallowing and coughing difficulties^1,2,9
• Shaking hands^2,9

For children aged 18 months–teens:^2,5

• People with this form of SMA may have poor balance, and have problems with standing up and walking/climbing stairs¹³

For adults aged >18 years:²

• In the mildest form, symptoms don’t appear until adulthood. People with this form of SMA typically have mild weakness, without breathing difficulties^13,14

Even if your baby seems happy and alert, if you feel there may be a problem, please see your doctor for help and information^1,5,15,16

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Signals for muscle movement are generated in the brain.¹ However, people with SMA have a genetic mutation that causes their lower motor neurons to deteriorate and stop working.^1–5 This means that signals in the brain are not carried from the spinal cord to the muscles.¹ If the muscles no longer receive signals telling them to move, they can waste away (atrophy) and become increasingly weaker.^1,4,5 This leads to difficulty with movement, breathing, feeding and speaking⁶

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There are currently no cures for SMA.¹ However, there are treatments available that can change disease outcomes for patients.^2,3 Speak to your doctor for more information about patient care⁴

Yes, there are medications available to treat SMA.¹ Speak to your doctor for more information about treatment options and patient care

Your doctor will be your first line of contact when treating SMA. They will refer you to any relevant specialists, such as a pediatric neurologist, and offer you information and advice^1,2

A genetic blood test is used to confirm a diagnosis of SMA in your child.^1,2 Additionally, it can also be used to test if both parents are a carrier of the faulty gene, which will help determine if there is a risk of having a child with SMA²

Yes, there are tests available that can be carried out during pregnancy if there is a risk you could have a child with SMA.¹ If the tests results show there is a likelihood of you having a child with SMA, you should speak to your doctor for further information and advice¹

Early diagnosis and treatment are extremely important in SMA to give your child the best chance in life^1,2

Yes, SMA Type 4 can affect adults over 18 years old.^1,2 This is the mildest form of SMA as symptoms don’t appear until adulthood^1,2

Adults with SMA Type 4 can experience mild weakness, without breathing difficulties¹