Spinal Muscular Atrophy (SMA) is a genetic disease that affects the part of the nervous system that controls voluntary muscle movement. Specifically, it involves a progressive deterioration of nerve cells (called motor neurons) in the spinal cord – hence the word spinal in the name of the disease. SMA is muscular because the loss of these nerve cells precludes the proper transmission of signals from the brain to the muscles – much like an electrical short prevents a light from turning on when you flip a switch. Atrophy is the medical term for the wasting or shrinkage of the muscles which generally occurs when there is limited or no activity.

SMA does not distinguish between age, race or gender. It is an autosomal recessive disease, which means that, in most cases, both parents must be carriers for a child to be affected.

There are several types of SMA, which are distinguished by when symptoms begin to show. Typically, the earlier symptoms manifest, the more severe the disease, and ultimately the greater the mortality rate. Following is a brief overview of the various types or classifications of SMA:

Type I SMA: Also known as Werdnig-Hoffmann Disease or Infantile SMA, Type I SMA is the most severe. Children with Type I tend to be weak and lack motor development, rendering movement difficult. Children afflicted with Type I cannot sit unaided and have trouble breathing, sucking and swallowing. Usually, symptoms begin to show between birth and six months.

Type II SMA: Slightly less severe than Type I, Type II patients may be able to sit unaided or even stand with support, and usually do not suffer from feeding and swallowing difficulties. However, they are at increased risk for complications from respiratory infections. Symptoms tend to show between seven and 18 months old.

Type III SMA: Also known as Kugelberg-Welander Disease, this is the least deadly form of childhood-onset SMA. Although Type III patients are able to stand, weakness is prevalent and patients tend to require the use of a wheelchair. Usually, symptoms begin to show after the age of 18 months, and can even surface in adulthood.

Type IV SMA: Symptoms usually begin in the hands, feet and tongue, and spread to other areas of the body. This is the adult form of the disease. Symptoms tend to begin after age 35.

Adult Onset X-Linked SMA: Also known as Kennedy's Syndrome or Bulbo-Spinal Muscular Atrophy, this type occurs only in men. Facial and tongue muscles are noticeably affected. In addition, these men also often have breast enlargement known as gynecomastia.  Like all forms of SMA, the course of the disease is variable, but in general tends to progress slowly.

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Diagnosing SMA usually starts with an exam performed by a pediatric neurologist. During the exam, the neurologist will look for the common physical characteristics of SMA which can include:

• Overall “floppy” or “rag doll” appearance

• "Frog" shaped legs (knees apart and legs bent)

• Poor posture and limited mobility

• Sunken or narrow chest

• Big belly

• Breathing with the belly instead of the lungs

• Weak cry and weak cough

• Poor to no head/neck control; head tilted to one side

• Weak or no movement of the legs and/or arms

• Not able to bear any or little weight on legs or arms

• Hands that remain clenched or turned the wrong way

• Difficulty with sucking and swallowing

• Tongue fasciculations (tongue vibrating rapidly)

Keep in mind that the severity of these characteristics can vary greatly in each child. Also, some symptoms may not show up until later as the disease naturally progresses.

Based on the exam, if the neurologist suspects SMA, he or she will most likely recommend a genetic blood test, which works by identifying deletions in gene sequences that are not missing in healthy children. Specifically, this test looks for deletions of both Survival Motor Neuron (SMN) genes which produced proteins needed for muscle movement. This test is 95% accurate in detecting these deletions which cause SMA, and no further testing is usually required.

For the 5% of children that do not show the gene deletions, the neurologist will most likely recommend an EMG (Electromyography) test performed. This test measures the electrical activity of muscle. In this procedure small needles are inserted into the patient's muscles, usually the arms and thighs, while an electrical pattern is observed and recorded. The readout is similar to that of an EKG or lie detector. In addition, a nerve conduction velocity (NVC) may also be performed. In this test the response of a nerve to an electrical stimulus is measured.

Sometimes a muscle biopsy might be recommended to confirm the diagnosis. A muscle biopsy is a surgical procedure where an incision, approximately 3 inches long, is made and a small section of muscle is removed, usually from the thigh. The biopsy is used to check for degeneration. Although many doctors may persuade you of the necessity of a general anesthetic, this procedure can be done with a local anesthetic. It is an especially important point when dealing with children who may be suffering from a neuromuscular disorder and may have weak respiratory function.

There is an alternative to the biopsy, a procedure known as a needle biopsy. Instead of a two to three inch incision, only a small nick in the skin is necessary. Be sure to inquire about this procedure.

In summary, the blood test is definitely the easiest, least painful and least invasive of all the options available to test for SMA. Furthermore, it accurately diagnoses SMA in 95% of cases.  However, if the blood test comes back negative for SMA, but the neurological exam still points to the possibility, then an EMG and even muscle biopsy will most likely be necessary. If the results of these tests come back positive, the diagnosis will be 100% accurate.

Having your child undergo testing for SMA can put significant stress on you and your family. Throughout the process, keep in mind that you should not be afraid or intimidated to ask questions of every medical professional who comes in contact with your child. Also, if something doesn’t seem or feel right, don’t hesitate to seek a second or even third opinion.

NOTICE: The information provided herein is for educational purposes only and should not be used in place of advice from a qualified medical professional. If you have a question about your specific situation, please consult your child's physician or other medical professional.