Spinal Muscular Atrophy (SMA) is a heritable neuromuscular disorder
that causes degeneration of the alpha motor neurons in the spinal cord.
In order to develop connections with muscle fibres, motor neurons need to produce
the SMN protein. SMA is caused by a defect in the survival motor neuron (SMN) gene, affecting the
nervous system responsible for voluntary muscle movement.
The SMN deficiency is due to the mutations in 5q chromosome, which can cause
physical weakness, movement loss, and, in some cases, new-born death if left untreated. Progression
of SMA can also affect breathing and swallowing, which can threaten the life of the patient.
Types of SMA
Spinal muscle atrophy is classified as type 1, 2, 3 or 4 depending on age of
onset. Most cases are progressive — that is, symptoms worsen instead of improving - but in general
the later the symptoms develop, the better the outcome for motor function.
SMA type 1 (Infantile-onset SMA or Werdnig-Hoffman
disease): This is the most severe kind of SMA ...and strikes infants within the first six months of life. Some
children with SMA type 1 will die before their second birthday, but aggressive
therapy is improving the outlook for these children.
SMA type 2 (Intermediate SMA): When a child develops
spinal muscular atrophy between six and 18 months, ...the condition is classified as type 2. The child may be able to sit
up, but respiratory challenges can shorten their lives as the disease
progresses.
SMA type 3 (Juvenile SMA, Kugelberg Welander
syndrome): Type 3 SMA emerges in children 18 months old ... or older and can become evident as late as in the
teenage years. Muscle weakness is present, but most patients can walk and stand
for limited periods, particularly early in the course of the
illness.
SMA type 4 (Adult SMA): In some people, SMA develops
in adulthood. Type 4 SMA is rarely severe enough to ...have impact on the patient’s lifespan.
Treatment Importance:
SMN is essential to normal motor function because it enables muscles to receive signals
from the nerves.
