What is SMA?


Spinal Muscular Atrophy (SMA) is a motor neuron disease. The motor neurons control the voluntary muscles that are used for activities such as crawling, walking, head and neck control, and swallowing. The loss of motor neurons results in muscle weakness and atrophy. SMA is a relatively common "rare disorder": approximately 1 in 6,000 babies born are affected, and about 1 in 40 people are genetic carriers.

SMA affects muscles throughout the body, although the proximal muscles (those closest to the trunk of one’s body - i.e. shoulders, hips, and back) are often most severely affected. Weakness in the legs is generally greater than in the arms. Sometimes feeding and swallowing can be affected. Involvement of respiratory muscles (muscles involved in breathing and coughing) can lead to an increased tendency for pneumonia and other lung problems. Sensation and the ability to feel are not affected. Intellectual activity is normal and it is often observed that patients with SMA are unusually bright and sociable. There are four types of SMA: SMA Type I, II, III and IV. The determination of the type of SMA is based upon the physical milestones achieved. It is important to note that the course of the disease may be different for each affected person.


What is Spinal Muscular Atrophy?

SMA is a deadly and relatively common genetic disease and is the leading genetic cause of death in infants and toddlers. It is the absence/defect in the Survival Motor Neuron Gene (SMN1) that causes Spinal Muscular Atrophy. The SMN1 gene codes for survival of motor neuron (SMN) protein, and this protein is critical to the survival and health of motor neurons, nerve cells in our spinal cord that our brain uses to control our muscles. Without sufficient SMN protein, motor neurons shrink and die. As the motor neuron network breaks down, the ability of the brain to control muscles diminishes and with less control and use, muscles weaken and waste away.
 
How does it affect children?
 
The decline of the motor neuron network, and the increased demand placed upon remaining motor neurons by children’s growing bodies, results in a progressive loss of muscle control and movement. In severe cases, the weakness is so great that death results either in the womb or within the first two years of life. Even in milder forms, SMA has a devastating and deadly impact on children. Victims either never acquire, or progressively lose, the ability to walk, stand, sit and eventually move. Children suffer increasing bone deformities, spinal deformities and ultimately fatal respiratory complications. Repeated surgery is often required to prolong life, which may include procedures such as tracheotomies to assist in breathing and eating and spinal fusion to mitigate spinal damage. Children's minds are unaffected, however, leaving their developing brains trapped in weakening bodies.

 
How common is SMA?
 
One in 35-40 Americans are carriers, or approximately 7 million people. Over 25,000 Americans are believed to suffer from SMA, comparable in prevalence to better-known diseases such as ALS (Lou Gehrig’s Disease) and Cystic Fibrosis. It is estimated that approximately 1 in 6,000 to 1 in 10,000 infants are born annually worldwide with SMA, and the incidence is similar to Duchenne Muscular Dystrophy and Tay Sachs Disease (in the Jewish population).