Professional Advice

August is Spinal Muscular Atrophy Awareness Month

BY: CDC, MDA, Cleveland Clinic.

  August is the month in which we increase everyone’s awareness of spinal muscular atrophy, which is a group of genetic neuromuscular disorders that cause some muscles to grow weak and waste away. This disease causes loss of a specific type of nerve cell called lower motor neurons, which are in the spinal cord. The loss of these motor neurons causes the muscles to not receive the nerve signals that can make them move. Severity of the disease can be attributed to age of onset, progression, and symptoms. SMA involves the weakness of voluntary muscles. This disease is one of the leading genetic causes of infant mortality and is the 2^nd most common severe hereditary disease of infancy after cystic fibrosis.

Spinal muscular atrophy is named as such because most of the nerve cells that control the muscles are in the spinal cord, the muscles are the most affected by the disease, and the disease causes muscle to atrophy, which means getting smaller. SMA is also called motor neuron disease because it causes loss of nerve cells in the spinal cord called motor neurons.

The are five subtypes of SMA and are classified based on the age of onset, severity, and life expectancy. These types range from SMA type 0 to SMA type 4. SMA type 0, type 1, and type 2 are fatal and will only survive for up to 30 years old, with respiratory issues as a major cause of death. SMA type 0 refers to a rare subtype that affects the fetus in the womb and causes respiratory failure at birth with a life expectancy no later than the first month of life.

SMA type 1 is the most common and represents about 60% of SMA cases. Symptoms arise within the first 6 months of life and include limited head control and decreased muscle tone. Due to difficulty swallowing and breathing, children with SMA type one die before their second birthday without breathing support. Patients with SMA type 2 show symptoms from 6 months to 18 months of life. It causes worsening muscle tone and weakness, which affects their legs more than their arms. Children with this type of SMA can sit but not walk and around 70% of people with type 2 will survive until 25 and some until their 30s.

Patients SMA type 3 and Type 4 typically don’t develop breathing issues and don’t affect life expectancy. SMA type 3 develops after the first 18 months of life and symptoms typically include muscle weakness which affect the lower limbs, leading to difficulty walking. SMA type 4 is the mildest form of SMA and most likely not to appear until the age of 21. The muscle weakness is slow to progress, so most people remain mobile, and it usually doesn’t affect life expectancy.  The most likely cause of death from this disease is respiratory issues.

The cause for chromosome 5-related SMA is a deficiency in motor neuron protein, also called SMN, which stands for “survivor of motor neuron.” Normal motor neuron function is dependent on this protein. The deficiency of this protein is caused by a genetic mutation of the SMN1 gene, which affects chromosome 5. SMN2 gene also produces a small amount of SMN protein and depending on how many copies of the SMN2 gene a person has the symptoms could be less severe. Non-chromosome 5 forms are caused by the mutations of genes other than SMN1.

SMA diagnosis starts with medical history and symptoms, followed by a physical and neurological exam, and finally confirmation is obtained with a genetic test, which can confirm 95% of SMA cases by identifying problems with the SMN 1 gene.

Unfortunately, at this time there is no cure for SMA and treatments for it only seek to manage symptoms, such as physical therapy, occupational therapy, assistive devices, speech therapy, feeding tube and assisted ventilation for breathing issues. Medication for SMA included gene replacement therapy, which may benefit children younger than 2, and disease modifying therapy, which stimulates the production of SMN2 protein.