Spinal Muscular Atrophy in Children: Causes, Symptoms, and Treatment

What is spinal muscular atrophy in children?

Spinal Muscular Atrophy (SMA) is a group of genetic neuromuscular disorders that primarily affects the motor neurons in the spinal cord and brainstem. A neuromuscular disorder is a condition that affects the neurons controlling voluntary muscle movements, leading to progressive muscle weakness, atrophy, or impaired function. SMA is most commonly diagnosed in children and can have a profound impact on their ability to perform essential motor functions. These include fundamental activities such as breathing, swallowing, and movement, which may become increasingly challenging as the condition progresses. The loss of motor neurons also affects the nerve cells that connect muscles to the spinal cord, further impairing muscle function.

Types of spinal muscular atrophy 

SMA is classified into several types based on the severity of symptoms and the age of onset at which they first appear. Here’s a breakdown of each type:

Causes of spinal muscular atrophy 

SMA is a genetic condition primarily caused by a mutation in the SMN1 gene on chromosome 5 (Survival motor neuron 1). This gene plays a crucial role in the production of the survival motor neuron (SMN) protein, which is vital for the health and function of motor neurons that helps us to control our muscles. In most cases, SMA is an autosomal recessive disease, meaning that a child must inherit two defective copies of the SMN1 gene, one from each parent, to develop the condition. Having a singular defective copy of the SMN1 gene will not result in SMA.

1. Carrier parents:

   • If both parents are carriers of the faulty SMN1 gene, they typically do not exhibit symptoms of SMA. However, with each pregnancy:

     • There is a 25% chance the child will inherit both faulty copies and develop SMA.

     • There is a 50% chance the child will inherit one faulty copy and one healthy copy. The child will be a carrier like the parents.

     • There is a 25% chance the child will inherit two healthy copies of the gene.

2. Prevalence of carriers:

   • Approximately 1 in 40 to 1 in 60 individuals in the general population is a carrier of the faulty SMN1 gene. Carrier screening and genetic counselling are recommended for individuals with a family history of SMA or for those planning to have children.

Symptoms of spinal muscular atrophy in children

The symptoms of SMA vary depending on the type and severity but generally share common characteristics such as spinal curvature. Here are some key symptoms of SMA in children: 

1. Muscle weakness and wasting:

   • Progressive weakness is most pronounced in the shoulders, hips, and back.

   • Muscle degeneration, or atrophy, becomes noticeable as the condition advances.

2. Loss of motor skills:

   • Infants with SMA may struggle to achieve developmental milestones, such as lifting their head, sitting up, or crawling.

   • In severe cases, motor skills may regress over time.

3. Respiratory difficulties:

   • Weakness in respiratory muscles leads to breathing challenges and reduced lung function.

   • Children with severe types often require respiratory support to manage these difficulties.

4. Feeding challenges:

   • Weak swallowing muscles can cause difficulty feeding, particularly in infants with more severe forms of SMA.

   • Poor feeding may result in inadequate nutrition and weight gain.

5. Poor muscle tone (Hypotonia):

   • A hallmark of SMA, hypotonia causes "floppiness," where muscles appear soft and lack resistance.

6. Skeletal deformities:

   • Weak back muscles often result in scoliosis (curvature of the spine) and other skeletal abnormalities over time.

If your child is showing any of these listed symptoms or have an existing medical history, it’s essential to seek professional advice promptly. Request an appointment with our paediatric neurologists at Thomson Medical today. We offer comprehensive diagnostic services and personalised care plans to help manage your child’s condition effectively. 

Diagnosis of spinal muscular atrophy in children

Diagnostic tests for spinal muscular atrophy in children involve a combination of advanced tests and evaluations to confirm the condition and assess its severity. Key methods of diagnosing SMA includes: 

1. Genetic testing:

   • The most reliable way to confirm SMA, detecting mutations in the SMN1 gene through a simple blood test.

2. Electromyography (EMG):

   • Measures electrical activity in muscles to assess motor neuron function, helping identify nerve-related muscle issues.

3. Muscle biopsy:

   • Rarely used today, this involves analysing a small sample of muscle tissue to check for abnormalities.

4. Newborn screening:

   • Included in many newborn screening programmes, enabling early detection and treatment to improve outcomes.

Early diagnosis is vital for the effective management of SMA. If your child shows symptoms or there is a family history of the condition, request an appointment with Thomson Medical today for an appropriate and personalised treatment plan.

Treatment options for spinal muscular atrophy

While there is currently no cure for SMA, advancements in treatment can significantly improve quality of life and, in many cases, prolong survival. Here are some treatment options for SMA: 

FDA-approved medications

• Nusinersen (Spinraza):

  • Delivered via spinal injection, this treatment boosts the production of the SMN protein to support motor neuron health.

• Onasemnogene abeparvovec (Zolgensma):

  • A gene therapy administered through an IV infusion, replacing the faulty SMN1 gene. Approved for children under two years old, it helps enhance motor function and strength.

• Risdiplam (Evrysdi):

  • An oral medication that increases SMN protein levels, suitable for both children and adults.

Supportive care options

• Physical therapy:

  • Helps maintain muscle strength and flexibility, preventing joint contractures.

• Occupational therapy:

  • Focuses on improving the ability to perform daily activities and fostering independence.

• Respiratory support:

  • Devices like ventilators or BiPAP machines assist with breathing challenges.

• Nutritional support:

  • Ensures adequate nutrition through specialised diets or feeding tubes for children with swallowing difficulties.

• Orthopaedic interventions:

  • Braces or surgical procedures may be required to address scoliosis or other skeletal abnormalities caused by weakened back muscles.

Assistive devices

Adaptive tools such as wheelchairs, braces, and specialised equipment can greatly enhance mobility, independence, and overall quality of life for children with SMA.

Prognosis and quality of life for children with spinal muscular atrophy

The outlook for children with SMA depends largely on the type of SMA and how early treatment begins. 

• Children with SMA Type 1 are living longer and achieving milestones that were once thought unattainable.

• Children with SMA Types 2 and 3 can often lead fulfilling and active lives when provided with the right medical support, therapies, and assistive devices.

Therefore, early diagnosis and intervention are crucial in improving the quality of life and outcomes for children with SMA. With proper care, many children can overcome challenges and thrive in their daily activities.

Prevention and genetic counselling for SMA in children

Although SMA is a genetic condition and cannot be prevented, proactive steps can help families better understand and manage the risks.

• Carrier screening: Genetic testing helps potential parents determine if they carry the faulty SMN1 gene that causes SMA.

• Prenatal and preimplantation diagnosis: These options allow families with a known risk to detect SMA before or during pregnancy.

Even though the gene mutation causing SMA cannot be changed, early detection through newborn screening and timely treatment can greatly improve outcomes and quality of life.

FAQ

Can SMA be cured?

No, there is currently no cure for SMA. However, treatments like gene therapy and FDA-approved medications can slow disease progression and improve quality of life.

How does gene replacement therapy work for SMA?

Gene replacement therapy, such as Zolgensma, delivers a healthy copy of the SMN1 gene to help the body produce more SMN protein. It is especially effective in very young children.

Is SMA always fatal?

Not necessarily. The outcome depends on the type and severity of SMA. Advances in treatments have significantly improved survival rates and quality of life for those with SMA Types 1, 2, and 3.

How is SMA inherited?

SMA is passed down in an autosomal recessive pattern, meaning a child must inherit one faulty SMN1 gene from each parent to develop the condition.

Can children with SMA attend school?

Yes, with appropriate accommodations, such as mobility aids and support for daily tasks, many children with SMA can successfully attend school and participate in educational activities.

What is the life expectancy for a child with SMA?

Life expectancy varies by type. Without treatment, Type 1 SMA may result in a shorter lifespan, while Types 2 and 3 often allow for longer lives, especially with supportive care and modern treatments.

Is physical therapy helpful for children with SMA?

Yes, physical therapy plays a crucial role in maintaining muscle strength and flexibility, though it does not stop the progression of the disease.

What roles do nutrition and feeding play in managing SMA?

Proper nutrition is essential, as muscle weakness can make eating challenging. High-calorie diets and feeding assistance, such as feeding tubes, may be needed to ensure adequate nutrition.

Is SMA painful?

SMA itself is not typically painful, but complications like joint stiffness or immobility may cause discomfort, which can be managed with proper care.

What is the latest research on SMA?

Current research focuses on improving gene therapy, developing new medications, and exploring genetic pathways. Ongoing clinical trials aim to enhance motor function and improve quality of life for individuals with SMA. Promising treatments, such as SMN-enhancing drugs and advanced gene-editing techniques, are offering hope for better management of the condition.

The information provided is intended for general guidance only and should not be considered medical advice. For personalised recommendations and tailored advice, please consult a specialist at Thomson Medical. Request for an appointment with Thomson Medical today.