Spinal Muscular Atrophy (SMA)

What is Spinal Muscular Atrophy (SMA)?

Spinal muscular atrophy (SMA) is a type of hereditary neuromuscular disorder. SMA causes muscle weakening and wasting (atrophy) especially in the middle part (proximal) and the lower part of the body. The disease is caused by the absence of a specific type of nerve cell in the spinal cord called motor neurons. Motor neurons are responsible for sending signals to the brain for muscle contractions. Without motor neurons, muscles cannot receive signals from the brain to make certain movements. That is why patients with SMA have smaller and weaker muscles due to lack of use.

SMA is a rare disease that only affects approximately 1% of the population in the United States. Although rare, about 1 in 50 Americans carry the mutated gene without knowing it. Carriers don’t develop SMA. However, if two carriers mate, there’s a 90% chance that their child will have SMA.

There are many types of spinal muscular atrophy. These types differ in age of onset and the severity of the symptoms. But symptoms can overlap between types. The most common symptoms of spinal muscular atrophy include: 

  • Small muscle tone
  • Weak heart and lungs
  • Weak bones and muscles
  • Delayed motor development
  • Immobility
  • Respiratory infections
  • Scoliosis
  • Involuntary movements of the tongue

Types Spinal Muscular Atrophy

Type 0: Spinal muscular atrophy type 0 is the morbid type of the disease. The symptoms of type 0 are evident as early as pregnancy. Children that have type 0 SMA are born extremely weak and do not survive past infancy. 

Type 1: Werdnig-Hoffman disease or type 1 SMA is a severe type and the most common of SMA. According to medical records, 60% of SMA patients suffer from type 1. Children that are born with type 1 SMA will have progressive symptoms and are likely to die before reaching 2 yrs old. 

Type 2: type 2 SMA, also called Dubowitz disease, is less aggressive compared to type 1 SMA. Symptoms of type 2 SMA will be obvious when a child is between 6 months to 1½ yrs old. Type 2 SMA affects the lower part of the body, particularly the legs. So children with type 2 SMA are bound to be in wheelchairs. Children with this type of SMA can live into adulthood.

Type 3: Kugelbert-Welander or juvenile-onset SMA is a mild type SMA. The onset of symptoms typically shows after a child’s first 18 months of life. Symptoms can affect the child’s ability to walk or stand. Most children with type 3 SMA can live a long and normal life. 

Type 4: Type 4 is a rare type SMA. This type usually affects adult individuals. Symptoms progress gradually that most individuals with Type 4 SMA live normal lives.

Treatment and Diagnosis

SMA symptoms can mimic other neuromuscular disorders. In order to get a proper diagnosis, your professional healthcare provider will perform a series of tests. He or she might conduct a physical examination and medical history checking. Some doctors might also suggest a thorough examination like EMG scanning and muscle biopsy. Prenatal tests can determine if an unborn child inherited SMA. 

Sadly, there is no known cure available for SMA. Patients with SMA undergo physical and occupational therapy to alleviate the symptoms. Many depend on assistive devices, such as orthopedic braces, crutches, walkers, and wheelchairs.

The best thing you can do is to take preventive measures before pregnancy to lower the chance of passing on SMA. A process called preimplantation genetic diagnosis (PGD) will help ensure that your child will not have mutated SMN1 genes. 

If you or your spouse has a family history of the disease, seek help from medical professionals. A genetic counselor can explain your genetic conditions. 


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