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 6000 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?
1 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).
