Spinal muscular atrophy (SMA) is a genetic disorder and causes the spinal and skeletal muscles to weaken and waste away. SMA is caused by a loss of nerve cells and by a mutation in the SMN1 gene. The more SMN1 genes that an individual has, the less severe muscular atrophy becomes. Symptoms of SMA can include breathing issues, delayed gross motor skills, limited mobility, and curvature of the spine. There are four types of spinal muscular atrophy which range from type I to type IV.

SMA can be diagnosed in two ways: genetic testing and muscle biopsy. Genetic testing is typically the first route to determine if an individual has spinal muscular atrophy. With genetic testing the SMN1 gene is examined to determine if there is any depletion or variations within the gene. A muscle biopsy involves a doctor taking a small piece of muscle in the affected area to check under a microscope.

The main types of SMA include:

1. Werdnig Hoffman disease
Werdnig Hoffman muscular atrophy is one of the three types of SMA known as juvenile spinal muscular atrophy. The severity of this type of muscular atrophy of the spine is high and categorized as Type I. Werdnig Hoffman spinal muscular atrophy can appear around three months of age and affects a child’s ability to crawl and walk.

2. Type II SMA
Type II muscular spinal atrophy makes itself known in the infant stage between six to 12 months of life. An infant will not be able to stand, but will be able to sit up on their own. Individuals with this form of SMA will require assistance when standing or walking.

3. Kugelberg-Welander SMA
This type of spinal muscular atrophy can show in children that are around 18 months old, but it can even appear in late adolescence. This type of SMA is classified as type III and is considered a mild form of SMA. Children with this form of muscular atrophy have weakened arm and leg muscles, but they are able to walk without assistance.

4. Type IV
The fourth type of SMA affects individuals in adulthood. Type IV involves mild muscle weakness in the body’s lower extremities. Sometimes the mild muscle weakness can move to the arms and shoulders. Usually, people with type IV SMA can walk on their own and rarely will individuals affected by this form of spinal muscular atrophy require assistance.