Spinal Muscular Atrophy: Causes, Symptoms, Complications, Treatment

Spinal muscular atrophy (SMA) or spinal muscular atrophy is a group of genetic disorders that make a person unable to control muscle movement due to loss of nerve cells in the spinal cord and brain stem.

SMA is a neurological condition and a type of motor neuron disease. This condition affects one in every 8,000–10,000 people worldwide Genetics Home Reference.

SMA causes muscle wasting and weakness. It will be difficult for the sufferer to stand, walk, control head movements, and in some cases it is difficult to breathe and swallow, citing Medical News Today. Some types of SMA are present at birth, while others appear later in life. Several types of SMA affect life expectancy.

1. Cause

Spinal Muscular Atrophy: Causes, Symptoms, Complications, Treatmentillustration of spinal muscular atrophy patient (flickr.com/Dan Perez)

The four types of SMA result from protein deficiency survival of motor neurons (SMN). Motor neurons are nerve cells in the spinal cord that are responsible for sending signals to muscles.

When a mutation (error) occurs in both copies of the SMN1 gene (one in each of the two copies of chromosome 5), it causes a deficiency of the SMN protein. If little or no SMN protein is produced, it will cause motor function problems.

The gene next door to SMN1 is called the SMN2 gene, which has a similar structure to the SMN1 gene. They can sometimes help compensate for SMN protein deficiency, but the number of SMN2 genes fluctuates from person to person. So, the type of SMA depends on how many SMN2 genes a person has to help “redeem” their SMN1 gene mutation.

If a person with SMA linked to chromosome 5 has more copies of the SMN2 gene, they can produce more of the functioning SMN protein. In return, their high school will be lighter with onset which is slower than someone who has fewer copies of the SMN2 gene.

2. Types and symptoms

Spinal Muscular Atrophy: Causes, Symptoms, Complications, Treatmentillustration of spinal muscular atrophy patient (flickr.com/EURORDIS – Rare Diseases Europe)

Reported Healthline, SMA consists of four types, namely:

1. High school type 1

SMA type 1 is called SMA with onset infantile or Werdnig-Hoffmann disease. Typically, people with this type of SMA have only two copies of the SMN2 gene, one on each chromosome 5. More than half of new SMA cases are type 1.

Babies with SMA type 1 begin to show symptoms within the first six months after birth. Symptoms may include weakness, drooping arms and legs (hypotonia), weak crying, problems moving, swallowing, and breathing, and an inability to lift your head or sit up without support.

Babies with SMA type 1 usually don’t last more than two years. However, with today’s advances in technology, kids with high school can last for several years.

2. High school type 2

Type 2 high school is also known as middle high school. In general, people with SMA type 2 have at least three SMN2 genes. Symptoms usually begin when a baby is between 7 and 18 months old, and tend to be milder than type 1.

Symptoms include weakness in arms and legs, inability to stand on their own, shaking of the fingers and hands, scoliosis, weak respiratory muscles, and difficulty coughing.

Although SMA type 2 can shorten life expectancy, most people with SMA type 2 can survive into adulthood and live a long life.

People with SMA type 2 must use a wheelchair. In addition, they may need equipment to help them breathe better at night.

3. High school type 3

SMA type 3 is also called SMA onset slow, mild, or Kugelberg-Welander disease. Symptoms of this type of SMA are more varied.

People with SMA type 3 generally have between four and eight SMN2 genes. Symptoms begin after 18 months of age. Usually diagnosed at 3 years of age, but age onset the exact one may vary. Some people may not experience symptoms until early adulthood.

People with SMA type 3 are usually able to stand and walk on their own, but they may lose the ability to walk as they get older.

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Other symptoms include balance problems, difficulty getting up from a sitting position, difficulty climbing stairs or running, and scoliosis.

SMA type 3 generally does not change a person’s life expectancy, but people with this type are at risk of being overweight. In addition, their bones become weak and break easily.

4. SMA type 4

SMA type 4 is also called SMA with onset mature. People with this type of SMA have between four and eight SMN2 genes, so they can produce normal amounts of the SMA protein.

This type is the rarest of the four types of SMA. Symptoms usually begin in early adulthood, generally after age 35. Symptoms may worsen gradually over time.

Symptoms include weakness in the hands and feet, shaking and muscle twitching, and difficulty walking. SMA type 4 does not change a person’s life expectancy, and the muscles used for breathing and swallowing are usually not affected.

Also Read: Clubfoot: Symptoms, Causes, Diagnosis, Treatment

3. Complications that can be caused

Spinal Muscular Atrophy: Causes, Symptoms, Complications, Treatmentillustration of spinal muscular atrophy patient (flickr.com/EURORDIS – Rare Diseases Europe)

Over time, SMA patients will experience progressive muscle weakness and loss of muscle control. Reported Cleveland Clinic, Potential complications of SMA can include:

  • Fractures, hip dislocations, and scoliosis (curvature of the spine).
  • Malnutrition and dehydration due to feeding and swallowing problems which may require feeding tubes.
  • Pneumonia and respiratory tract infections.
  • Weak lungs and breathing problems that may require assisted breathing (ventilation).

4. Diagnosis

Spinal Muscular Atrophy: Causes, Symptoms, Complications, Treatmentgenetic test illustration (unsplash.com/Emin BAYCAN)

Some of the symptoms of SMA resemble those resulting from neuromuscular disorders such as muscular dystrophy. To find the cause of the symptoms, the doctor will perform a physical examination and examine the patient’s medical history.

In addition, the doctor may order one or more of the following tests to confirm the diagnosis of SMA:

  • Blood test: Enzyme and protein blood tests can check for high levels of creatine kinase. Weakened muscles release these enzymes into the bloodstream.
  • Genetic test: This blood test identifies problems with the SMN1 gene. As a diagnostic tool, the genetic test is 95 percent effective at finding the altered SMN1 gene.
  • Nerve conduction test: An electromyogram (EMG) measures the electrical activity of muscles and nerves.
  • Muscle biopsy: A doctor can perform a muscle biopsy, but this is rarely done. This procedure involves removing a small amount of muscle tissue and sending it to a laboratory for examination. A biopsy may show muscle atrophy or loss.

If the patient is pregnant and has a family history of SMA, prenatal testing can determine if her unborn baby has the disease. However, these tests slightly increase the risk of miscarriage. Prenatal tests for SMA may include:

  • Amniocentesis: During amniocentesis, the obstetrician will likely insert a thin needle into the patient’s abdomen to remove a small amount of fluid from the amniotic sac. The lab specialist (pathologist) examines the fluid for SMA. This test is done after the 14th week of pregnancy.
  • Chorionic villus sampling (CVS): The obstetrician takes a small tissue sample from the placenta through the mother’s cervix or abdomen. The pathologist will examine the sample for SMA. CVS can be done as early as 10 weeks of gestation.

5. Treatment

Spinal Muscular Atrophy: Causes, Symptoms, Complications, Treatmentillustration of spinal muscular atrophy patient (flickr.com/North Charleston/Councilman Ron Brinson)

There is no cure for high school. The available treatments can only help improve the patient’s quality of life.

Treatment will depend on the type and symptoms of SMA. Many patients benefit from physical and occupational therapy, as well as assistive devices such as orthopedic assistive devices, powered wheelchairs, crutches, walkers, ventilators, and modified access to computers. These assistive devices enable SMA patients to live longer, be more active, and participate more in the community.

The following treatments may also help:

  • Disease-modifying therapy: This drug stimulates the production of the SMN protein. Nusinersen (Spinraza) is a drug for children aged 2 to 12 years and can be used for all types of SMA. Doctors inject four initial doses over two months, followed by a recovery dose for four months. The doctor injects medicine into the space around the spinal canal. This is a class of drugs called antisense oligonucleotide (ASO), which aims to target the underlying problem by influencing RNA production. Spinraza appears to slow the progression of SMA and may reduce muscle weakness, but its effectiveness may vary between individuals. A different drug, risdaplam (Evrysdi), helps adult patients and children over two months of age. This drug is taken orally every day.
  • Gene replacement therapy: Children under 2 years of age may benefit from an intravenous (IV) infusion of a drug called onasemnogene abeparvovec-xioi (Zolgensma). This therapy replaces the missing or damaged SMN1 gene with a functioning gene.

That’s a row of facts about spinal muscular atrophy or spinal muscular atrophy. The quality and life expectancy of patients varies, depending on the type of patient.

Babies with SMA type 1 usually die before their second birthday. Children with SMA type 2 or 3 can live full lives, depending on the severity of symptoms. People who develop SMA during adulthood (type 4) often remain active and enjoy a normal life expectancy.

Also read: Progressive Genetic Muscle Disorders, These are 9 Categories of Muscular Dystrophy

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