Muscle-controlling nerve cells (motor neurons) are located mostly in the spinal cord. Long, wirelike projections connect the motor neurons to muscles in the limbs and trunk. Normally, signals from the neurons to the muscles cause muscles to contract. In SMA, motor neurons are lost, and muscles can’t function.
The first steps in diagnosis of a neuromuscular disease are usually an in-office physical examination and family history, with some simple tests to distinguish spinal muscular atrophy (SMA) from similar conditions (such as muscular dystrophy).
SMA linked to chromosome 5 (SMN-related), types 1-4
In SMA types 1 through 4, symptoms vary on a continuum from severe to mild, based on how much SMN protein there is in the nerve cells called motor neurons. (SMN stands for survival of motor neuron.) The more SMN protein there is, the later in life symptoms begin and the milder the course of the disease is likely to be.
Spinal muscular atrophy types 1 through 4 all result from a single known cause — a deficiency of a protein called SMN, for "survival ofmotor neuron."
Deficiency of SMN protein occurs when a mutation (flaw) is present in both copies of the SMN1 gene — one on each chromosome 5. Normally, most of the protein made from SMN1 genes is full-length and functional, but when mutations occur, little or no full-length, functional SMN protein is produced.
MDA leads the search for treatments and therapies for spinal muscular atrophy (SMA). The Association also provides comprehensive supports and expert clinical care for those living with SMA.
In this section, you’ll find up-to-date information about spinal muscular atrophy, as well as many helpful resources. This information has been compiled with input from researchers, physicians and people affected by the disease.