Spinal Muscular Atrophy

About Spinal Muscular Atrophy

Spinal muscular atrophy (SMA) is a genetic disorder in which nerve cells in the spinal cord and brain stem degenerate, causing progressive muscle and wasting. The protein called SMN (survival of motor neuron) is found on both copies of the SMN1 gene. SMA is characterized by weakness and wasting (atrophy) in muscles used for movement (skeletal muscles).Weakness tends to be more severe in the muscles that are close to the center of the body (proximal) compared to muscles away from the body’s center (distal). The muscle weakness usually worsens with age. The SMN2 gene is found throughout the body, but has the highest levels in the spinal cord.

There are three types of SMA where symptoms first appear during infancy and childhood, type I SMA, also called Werdnig-Hoffman disease, is apparent by age 6 months accounts for more than half of new cases; type II (intermediate) SMA typically develops between age 3 and 15 months; type III SMA, also called Wohlfart-Kugelberg-Welander disease, begins between age 15 months and 19 years and worsens slowly. Type IV SMA first appears between the ages of 30 and 60 years old. Other names for this condition includes: 5q SMA, proximal SMA, SMA, SMA-associated SMA, spinal amyotrophies, spinal amyotrophy, spinal muscle degeneration, spinal muscle wasting, and infantile onset.