Spinal Muscular Atrophy

Signs and Symptoms
Diagnosis
Treatment

Diagnosis

Your doctor will conduct a thorough physical exam of your child, as well as a family history. These are very important steps in making a diagnosis of spinal muscular atrophy (SMA) and in understanding your child's pattern of symptoms. To make a definite diagnosis and rule out other disorders, your doctor will recommend tests that may include:

• Genetic Testing

  Over the past decade, the genetic defects underlying SMA have been identified. Two genes that contribute to SMA are the "survival motor neuron gene (SMN)" and the "neuronal apoptosis inhibitory protein gene (NAIP)." In over 95 percent of patients with SMA, changes in the SMN gene are detected. Although we don't fully understand how the gene abnormality produces the disease, the discovery of the SMN gene has allowed doctors to make a definite diagnosis of SMA, provide specific genetic counseling to those affected as well as to SMA carriers, and has led to a number of research projects involving patients to test new treatments.

• Electrodiagnostic Tests

  This test consists of two parts -- nerve conduction studies and electromyography (EMG). During nerve conduction studies, electrodes are placed on the skin over a peripheral motor or sensory nerve. A small electric shock is emitted that may cause mild discomfort. This electrical impulse stimulates sensory and motor nerves and a recording is made from the electrodes to see how much of the impulse reaches the nerve and how fast the electricity is carried.

  EMG involves inserting a needle electrode through the skin to measure the bioelectrical activity of muscles. It also can determine if peripheral nerves have been damaged.

• Muscle and Nerve Biopsy

  A muscle biopsy was commonly used in the past to diagnosis of SMA and may be necessary if genetic testing fails to confirm a diagnosis. During this procedure, a small sample of muscle and nerve tissue is surgically removed from a patient. The sample is examined to see if the tissue shows signs of the disease.

Reviewed by health care specialists at UCSF Children's Hospital.
Last updated August 15, 2007