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Types of the SMA Disease

SMA or spinal muscular atrophy is a group of genetic disease that causes weakness and wasting of voluntary muscles. A person suffering from SMA cannot control the movement of their muscles. One of the major reasons a person suffers from this disease is the loss of nerve cells in the spinal cord and brainstem. Surveys suggest that one in every 5,000 to 10,000 infants around the world is born with this disease.

In more than 90 percent of cases, SMA is caused due to inadequate production of Survival Motor Neuron (SMN), which is a protein essential for specialized nerve cells called motor neurons.

The protein is produced by SMN1 and SMN2, which are present in the genes on chromosome 5. Typically, people have two copies of the SMN1 gene and multiple copies of SMN2 in each of the motor neuron cells. In people suffering from the SMA disease, both the copies of the SMN1 gene are missing or altered. Having additional copies of the SMN2 gene is associated with milder forms of the disease. Here are the three main types of the SMA disease you need to know:

SMA1
The severe form of SMA, it is also called the Werdnig-Hoffman disease. SMA1 is the most common type of SMA and is usually evident at birth or within the first few months of birth.

Patients suffering from SMA1 are usually up to six months old. The symptoms include weak trunk movement and floppy limbs. Toddlers with this type of disease have a very limited ability to move. They also face difficulty in holding their heads up and swallowing. SMA1 progresses rapidly and weakens the muscles, leading to frequent respiratory infections, and it can even cause death by the age of 2.

SMA2
The symptoms of this type of SMA appear between the ages of 7 to 18 months, and the rate of progression varies. The disease affects a child’s legs, as a result of which children suffering from SMA2 can never stand and suffer from respiratory infections. The life expectancy of children suffering from SMA2 can be up to adulthood, depending on the severity of the condition.

SMA3
Also known as the Kugelberg-Welander disease or juvenile SMA, it is the mildest version and can affect a child from 18 months to adulthood. Children suffering from this version can stand and walk, but they may have trouble getting up from a sitting position and experience muscle weakness.

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