Spinal Muscular Atrophy

Your doctor will conduct a thorough physical exam of your child, as well as record a family medical 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 the following tests:

Genetic Testing

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, genetic defects or changes in the SMN gene are detected.

Although we don't fully understand how the gene abnormality causes the disease, the discovery of the SMN gene has allowed doctors to make a definite diagnosis of SMA and provide specific genetic counseling to those affected as well as to SMA carriers. It has led to a number of research projects, including developing and testing new treatments in patients.

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. 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 diagnose SMA. It 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 Benioff Children's Hospital.

Related Information

UCSF Clinics & Centers

Pediatric Brain Center

Neuromuscular Clinic
1825 Fourth St., Sixth Floor
San Francisco, CA 94158
Phone: (415) 353-7596
Fax: (415) 353-2400
Appointment information