Spinal Muscular Atrophy (SMA): A Parent’s Role in Early Detection & Care

Spinal Muscular Atrophy (SMA) a progressive neurodegenerative disease that affects the motor nerve cells in the spinal cord and impacts the muscles used for activities such as breathing, eating, crawling, and walking. In Singapore, as in many other countries, it is a growing concern due to advancements in genetic testing and newborn screening programmes.

According to Dr Jocelyn Lim, consultant paediatric neurologist at KK Women’s and Children’s Hospital (KKH), SMA affects one in 12,000 live births in Singapore. While rare, understanding the condition is crucial for parents and caregivers, as early diagnosis and appropriate interventions can significantly improve a child’s quality of life. Dr Lim helps shed light on SMA, providing insights into its causes, symptoms, and the latest treatment options.

1. What is Spinal Muscular Atrophy (SMA)?

SMA is a rare genetic disease where nerves that control muscle movement are lost. As a result, muscles get weaker over time.

There are three main types of SMA, primarily based on the onset of symptoms and disease severity.

Type 1: This is the most severe type and usually presents by 6 months of age. These babies have severe weakness affecting their ability to control their head movement and sit independently. They have a weak cry and difficulty feeding and swallowing, which results in poor weight gain. Without treatment, they have a poor prognosis and rarely survive beyond two years.

Type 2: This presents between 6 and 18 months old and is less severe than Type 1. Babies can achieve independent sitting, but cannot stand or walk and are wheelchair dependent. They often have frequent respiratory, feeding, and orthopaedic complications that place significant financial and emotional burden on caregivers and families.

Type 3: Patients present later, anywhere from 18 months and 10 years. They can walk independently, though they get weaker over time and may lose their ambulation.

Abstract of motor neurons — *Image: vecstock on Freepik*

2. What causes SMA?

Special nerves, called motor neurons, require a protein called survival motor neuron (SMN) protein to work properly. This protein is coded for by the SMN gene. In patients with SMA, the main SMN gene (SMN1) is either missing or faulty and cannot produce SMN protein.

A second back-up SMN gene (SMN2) can only produce small amounts of SMN protein. As a result, motor neurons lose their function over time, and this results in muscles getting weaker.

3. How do I know if my unborn child is at risk for SMA?

Children inherit two copies of the SMN1 gene, one from each parent. In most cases of SMA, both copies inherited are faulty, resulting in the disease. If only one faulty gene is inherited, these individuals are known as carriers but do not show signs of SMA. In Singapore, about 1 in 50 carry the disease mutation.

Parents can test for their carrier status, even prior to conception. If both parents are carriers, there is a 25 per cent chance of their offspring inheriting both faulty copies and developing SMA.

4. What are the early signs parents should look out for?

About 60 per cent of SMA patients present as Type 1 by 6 months of age so it is important for parents to be aware of the early signs and symptoms SMA presents with. These include:

Poor head control – Baby has difficulty lifting their head, turning from side to side, and holding it upright.
Weak legs and arms with reduced activity and movement – Baby appears ‘floppy’, and legs are in a ‘frog leg’ position, with little or weak kicking.
Difficulty feeding and/or swallowing – Baby takes a longer time to complete their feeds, has difficulty sucking, and exhibits poor weight gain. Tongue tremors can be observed.
Weak cry and cough – Baby’s cries are soft and weak, and has difficulty coughing.

Upset infant — *Image: Ольга Макарова on Pexels*

5. Is SMA treatable?

While there is no cure for SMA, there are now new disease-changing therapies. These can significantly improve motor function, and reduce respiratory, nutritional, and orthopaedic complications. If treatment begins before the onset of symptoms, patients can achieve age-appropriate motor milestones.

Hence if parents notice the above signs, they should bring their child to a paediatrician or neurologist early, so that a timely diagnosis can be made.

6. How is SMA diagnosed?

Diagnosis requires a simple blood test that detects the presence of the SMN1 gene. If the SMN1 gene is absent or defective, the same test can predict the severity of SMA, depending on the number of copies to the SMN2 gene.

7. If my child is diagnosed with SMA, what happens next?

A primary neuromuscular specialist, together with a multi-disciplinary team, will care for your child. These include respiratory, orthopaedic, and endocrine physicians, therapists, a specialty nurse coordinator, dietician, and medical social worker.

Regular therapy is essential to strengthen muscles and maintain range of motion and muscle function. A wide range of assistive technology is also available to support patients with seating and mobility.

Parents' hands supporting baby's feet — *Image: Putulu Ningombam on Pexels*

8. How can I best support my child’s development?

There are many aspects to consider, including physical and emotional needs. Proper nutrition, with breastfeeding for instance, and later introducing solid foods, is vital for baby’s growth. Supervised tummy time can help strengthen baby’s neck, shoulder, and arm muscles.

Sufficient sleep and rest for you and your spouse is also important to ensure you can continue to care for and bond with baby. All this is true for a healthy baby, but especially crucial for one with SMA or other special needs.

While every baby develops at their own pace, there are specific age-appropriate milestones that are detailed in your health booklet you can refer to. If there are worrying signs of floppiness or weakness as mentioned above, please do not hesitate to consult your doctor for a review early.
– Dr Jocelyn Lim, Consultant, Neurology Service, KKH

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