Spinal muscular atrophy is one of the most common genetic causes of death in infants, but it may appear at different stages of life and with varying degrees of severity. It is a rare disease that affects the motor neurons in the spinal cord, leading to gradual weakness and atrophy of the muscles. Follow with us this article. We will shed light on the causes of the disease, diagnostic methods, and treatments available at Al Mousa Specialist Hospital, in addition to tips for living with this disease.  

What is spinal muscular atrophy

It is one of the rare genetic diseases that mainly affects the nervous system and muscles, leading to gradual muscle weakness and atrophy.

The disease occurs as a result of a mutation in the Survivor Motor Neuron 1 gene (SMN1), which is the gene responsible for producing a vital protein called the SMN protein, which motor neurons need to stay alive and which are responsible for sending signals from the brain and spinal cord to the muscles to control their movement and work properly.

Causes of spinal muscular atrophy

The main cause of spinal muscular atrophy is genetics, meaning that the patient inherits a defect in the survivor motor neuron 1 gene, which causes the production of an insufficient amount of the SMN protein, which is responsible for nourishing the motor neurons that send signals from the brain and spinal cord to the muscles, allowing us to move and perform daily activities such as walking, breathing, and swallowing.

Insufficient production of SMN protein causes motor neurons to shrink and die, making the patient's brain unable to control voluntary movements, especially the movement of the head, neck, chest and legs.

There is also a role for the SMN2 gene, which has an impact on the severity of the disease. It is the reserve gene for SMN1, as it can also produce the SMN protein, but in a small amount and is less effective. The more copies of the SMN2 gene, the greater the amount of SMN protein produced and the less severe symptoms of the disease appear.

Read also: Diagnosis of hereditary muscular dystrophy And treatment methods

Symptoms of spinal muscular atrophy

There is a variation in the symptoms of the disease among those affected, and the earlier the symptoms appear, the more severe they are. Symptoms vary depending on the type, as there are five subtypes of spinal muscular atrophy, which are as follows: 

1. Spinal muscular atrophy type 0 or congenital spinal muscular atrophy

It is a rare subtype of spinal muscular atrophy that affects the fetus before birth, and its symptoms include:

• Lack of fetal movement during pregnancy. 
• Joint curvature. 
• Severe muscle weakness and decreased strength. 
• Severe and serious respiratory problems. 

2. Spinal muscular atrophy type 1 or severe spinal muscular atrophy

It is called Werding-Hoffmann disease and represents about 60% of cases of the disease, and its symptoms appear during the first six months of life, in the form of:

• Head sluggish and difficult to control. 
• Severe weakness in all muscles of the body. 
• Weak crying and a faint voice. 
• Difficulty in breastfeeding and swallowing, which leads to malnutrition and weight loss. 
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• The infant is unable to sit without support, and does not gain the ability to crawl or walk. 
• Joint cramps. 
• Stiffness of the child's lower jaw joint. 

3. Spinal muscular atrophy type II or moderate spinal muscular atrophy

 It is called Dubowitz's disease, and its symptoms appear between the ages of six and eighteen months, and include:

• Noticeable muscle weakness, but less severe than the second type.
• The child can sit without assistance, but needs assistance to stand or walk. The weakness of the leg muscles is greater than the weakness of the arm muscles.
• Slight trembling in the fingers.
• Weakness in the respiratory muscles, leading to recurrent chest infections.
• Spinal curvature, which is common with age due to weak back muscles.
• Joint stiffness due to lack of movement.

4. Spinal muscular atrophy type III or mild spinal muscular atrophy

 It is called Kugelbert-Welander disease, and its symptoms appear after the first 18 months of the child’s life and include:

• The patient can walk independently at first, but may experience increasing difficulty with age.
• Difficulty climbing stairs or running.
• Muscle weakness, especially the legs, more than the arms at first.
• Slight tremor in the fingers.
•  Scoliosis and joint contractures may occur with age.
• Respiratory problems are less common or less severe than other types, but may appear in the later stages.

5. Spinal muscular atrophy type IV

This type is the mildest form of muscular dystrophy, and symptoms usually do not appear until after the age of twenty-one, and include:

• Mild to moderate muscle weakness, which develops very slowly, and mainly affects the muscles close to the body, such as the thighs and shoulders.
• The patient can walk and maintain his independence for a long time.
• The effect on breathing and swallowing functions is limited.

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Diagnosis of spinal muscular atrophy

At Al Mousa Specialist Hospital, the diagnosis of muscular dystrophy is a comprehensive approach that combines clinical examination, medical history, and a number of specialized diagnostic tests. 

The primary goal is to confirm the presence of the genetic mutation causing the disease and rule out similar cases. Diagnostic steps include the following:

• Clinical evaluation and medical history: The doctor asks the patient or the parents in the case of children about the symptoms observed, and about the presence of any previous cases of spinal muscular atrophy or other neuromuscular diseases in the family.
• Physical and neurological examination: The doctor examines the patient to evaluate muscle strength, reflexes, muscle relaxation and joint movement.
• Genetic testing: It is the main and most accurate test to confirm the diagnosis of muscular dystrophy. It is done by taking a blood sample from the patient. The test looks for the presence of a deletion or mutation in the SMN1 gene, which is responsible for muscular dystrophy, and determines the copies of the SMN2 gene to determine the severity of the disease and its prognosis.
• Electromyography (EMG): To measure the electrical activity of the muscles.
• Nerve conduction studies (NCS): To measure the speed and strength of electrical signals traveling through nerves.
• Additional blood tests: Measure the enzyme creatine kinase that leaks from damaged muscles, which helps differentiate between muscular dystrophy and other muscle diseases.

Treatment of spinal muscular atrophy

Unfortunately, there is no specific and definitive treatment for spinal muscular atrophy, but its treatment has witnessed tremendous developments in recent years, which has radically changed the course of the disease. Modern treatments for spinal muscular atrophy are divided into two main categories: disease-modifying therapies and supportive care. 

Disease-modifying therapies aim to address the root cause by increasing the production of the SMN protein, which is necessary for motor neurons to survive, or by replacing the defective gene. Treatments include:

• Nusinersen: It is a treatment that modifies the way the reserve gene SMN2 is processed to produce more functional SMN protein. It is given by direct injection into the fluid surrounding the spinal cord. It requires initial loading doses of 4 doses over approximately two months, then maintenance doses every 4 months for life.
• Onasemnogene Abeparvovec: It is a unique gene therapy. It works by delivering a functional copy of the defective SMN1 gene to motor neurons using a modified virus. It is given as a single intravenous injection once in a lifetime. It is primarily approved to treat children under two years of age, especially those with type 1 muscular dystrophy. It may be used for some other cases based on certain criteria. It is one of the most expensive treatments in the world due to its revolutionary nature and dose.
• Risdiplam: It is an oral small molecule drug that modulates the delivery of the SMN2 gene to increase the production of functional SMN protein. It is administered orally daily (liquid).

While supportive care plays a vital role in managing symptoms of spinal muscular atrophy and improving patients' quality of life, it includes the following:

• Physical therapy, to maintain joint flexibility, prevent muscle spasms, and improve range of motion.
• Occupational therapy focuses on helping patients develop or maintain the skills needed to perform daily activities. 
• Respiratory support, such as chest physical therapy, suctioning of secretions, cough aids, or the use of ventilators.
• Nutritional support: Because affected children have difficulty swallowing, which leads to malnutrition, the dietitian recommends dietary modifications or, in some cases, the use of feeding tubes to ensure that the child receives adequate nutrition.
• Bone and joint care, monitoring and treating complications such as spinal curvature and hip dislocation.
• Psychosocial support for patients and their families to cope with the emotional and social challenges associated with the disease.

Complications of spinal muscular atrophy

Muscular atrophy greatly affects various body functions, especially those that depend on voluntary muscle movement. Therefore, as the disease progresses, many complications appear that differ in severity depending on the type of atrophy and its effect on the individual. The main complications of spinal muscular atrophy include the following:

• Weakness of the breathing muscles: This is one of the most serious complications, especially in the more severe types such as types I and II, which makes breathing superficial and difficult, and leads to respiratory failure in severe cases that requires artificial respiration support.
• Recurring respiratory infections: As a result of weak coughing muscles and the patient’s inability to expel secretions from the lungs, which increases the risk of pneumonia and bronchitis.
• Sleep apnea: which affects sleep quality and oxygen levels.
• Difficulty swallowing: due to weak muscles of the mouth, throat, and tongue, which increases the risk of food and liquids entering the airways, malnutrition, weight loss, and dehydration.
• Esophageal reflux: due to weakness of the muscles surrounding the esophagus.
• Spinal curvature: due to weakness of the trunk muscles that support the spine, which leads to its curvature.
• Joint contractures: stiffness and restriction of joint movement. 
• Hip dislocation: Partial or complete dislocation may occur due to weakness of the surrounding muscles.
• Constipation and bloating: a result of weak abdominal muscles and lack of physical activity. 

Learn: Everything you need to know about Treating muscle tears

How to prevent spinal muscular atrophy

It is a hereditary disease, and its prevention is not done by traditional methods of preventing infectious diseases or those resulting from environmental factors, but rather prevention focuses on identifying genetic risks before or during pregnancy.

Available prevention methods are:

• Genetic testing before marriage or before pregnancy.
• Preimplantation genetic diagnosis, for couples who are both known to be carriers of the defective spinal muscular atrophy gene and want to have an unaffected child.
• Prenatal diagnosis, for couples who have a known risk of having a child with muscular dystrophy.    

Frequently asked questions

Are there cases of muscular dystrophy that have been cured?

 There is currently no completely curative treatment for spinal muscular atrophy, a complete cure that completely restores the defective genes to normal and eliminates the disease from the body.

However, there are some cases that have responded amazingly to treatment, especially if treatment is started very early. Currently available treatments such as Zolgensma, Spinraza, and Evrisdi do not cure the disease in the traditional sense, but they work:

•  Increases the production of SMN protein.
• Slowing the progression of the disease. 
• Improving motor functions. 
• Improvement in breathing and swallowing functions.
• Significant improvement in quality of life and life expectancy. 

Can a patient with muscular dystrophy walk?

The ability to walk for muscular dystrophy patients depends largely on the type and severity of the disease, the number of copies of the SMN2 gene, and, most importantly, whether and when they are receiving modern treatments.

Children with type 1 and type 2 muscular dystrophy do not gain the ability to walk at all, because the muscle weakness is severe. 

Patients with type 3 are initially able to walk, however, they may have difficulty with activities such as climbing stairs, running, or getting up from a sitting position.

While patients with type 4 can walk in general, symptoms are mild and develop very slowly in adulthood.

Can muscular dystrophy patients get married? 

This depends on the type and severity of muscular dystrophy, as some types affect the ability to perform daily activities including sexual activities, and some individuals may need additional support or lifestyle modifications.

In conclusion, spinal muscular atrophy represents a major challenge for patients and their families, but with every scientific advance, hope increases for improving the quality of life of those affected by this rare disease, and the role of specialized medical institutions such as Al Mousa Specialist Hospital is highlighted as a fundamental pillar in providing comprehensive and advanced care.

The hospital offers the latest treatments, in addition to physical and occupational therapy programs designed specifically for each patient.

Do not hesitate to visit us to obtain optimal advice and treatment, and you can contact us on our numbers listed on the website for more details, reservations and inquiries.

Sources 

Spinal Muscular Atrophy (SMA) – kidshealth

Spinal muscular atrophy – medlineplus