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Spinal Muscular Atrophy (SMA)
Monday, 21 July 2003
Thursday, 05 February 2004

What

SMA is a rare genetic motor neuron disease caused by degeneration of motor neurons in the spinal cord. Nerve cells called motor neurons control how the various muscles of the body move to carry out their functions. This progressive disease results in weakness and wasting of voluntary muscles (muscles that you can control). There are 3 different types of SMAs with different symptoms. In general, the nerves in the spinal cord and its associated system of nerves that control the muscles gradually lose their ability to stimulate the voluntary muscles to move and lose their strength which in turn causes the muscles to atrophy or deteriorate and waste away.

Who

The different forms of SMA affect different people at different ages. Type 1 (also called Werdnig-Hoffman) is the most severe form with the earliest onset. Symptoms are present in the early months of the child’s life. For type 2 SMA the onset is between 6 and 18 months old. Type 3 SMA (also called Kugelberg-Welander) begins after 18 months of age. The last type of SMA, type 4, is the milder type and begins in adulthood. All of the childhood SMAs are inherited. Each of the child’s parents carry a defective gene which they pass on to their child, therefore 2 copies of the gene are needed in order for the disease to develop.

Signs and Symptoms

Each type of SMA presents with different symptoms and are presented separately:

  • Type 1- “floppiness” of the arms, legs, and trunk. Impaired ability to swallow, breath, and feed. Symptoms appear before 6 months of age.
  • Type 2 (intermediate SMA) - respiratory problems, twitching of the arms, legs, or tongue, floppy limbs, and decreased or absent nerve reflexes. The muscles that are closer to the body are affected, for example the thigh will be weaker than the calf. The hands may be affected but stay strongest for the longest period of time. The spine of the child may begin to curve very early in life. The symptom with the greatest danger is respiratory muscle weakness which may greatly affect the child’s breathing.
  • Type 3 - abnormal walking, tremor of the fingers, difficulty running and climbing stairs. Scoliosis (curvature of the spine) and respiratory concerns remain high..
  • Type 4- occurs later in life with a variety of symptoms such as weakness of muscles in the face and tongue, speech impairment, and difficulty swallowing.

Possible Causes

SMA is caused by mutations in the SMN gene (chromosomal locus 5q11-q13). SMN (survival of motor neurons ) is a motor neuron protein that is necessary for normal nerve functioning.

Diagnosis

Physical examination, a detailed family history, and specific tests are needed in order to diagnose SMA. The diagnosis of SMA is suspected in individuals with poor muscle tone, symmetric muscle weakness that spares the face and ocular muscles, and evidence of anterior horn cell (i.e., lower motor neuron) involvement, including fasciculation’s of the tongue and absence of deep tendon reflexes. A blood test for an enzyme called creatine kinase (CK) will be elevated because this enzyme leaks out of the muscle when it is deteriorating. However, this test is not specific for SMA since CK’s are high for a number of neuromuscular diseases. Genetic testing will probably be ordered if SMA is suspected. Genetic tests that look for deletions or an absence of the SMN gene are the most accurate way to diagnose SMA. A blood sample is the only thing that the child needs to provide in order to undergo genetic testing. Other tests may be conducted to measure nerve conduction velocity. Molecular genetic testing is clinically available and is used to confirm the diagnosis of SMA and to provide genetic counseling to at-risk family members.

Treatment

Since all forms of SMA are different, the treatments will also be different. Type 1 SMA is the most severe form but recent technology can improve the outcome of those afflicted with this form. Mechanical ventilation (breathing machines) assists respiratory effort and feeding tubes bypass the need to chew and swallow, thus prolonging the life of the child with type 1 SMA. Physical therapy preserves muscle mass and strength. Walking aids, lightweight leg braces, and standing frames provide support and greatly benefit children with type 2 in upright positions. Many children will use a power wheelchair to help them get around. Since the greatest danger to a child with type 2 continues to be respiratory muscle weakness, mechanical breathing assistance is often necessary at home and school. Respiratory assistance can come in the form of a face mask or mouthpiece through which air is delivered under pressure. Or the child may need a tracheostomy (opening into the windpipe or trachea) through which the pressurized air is delivered directly to the lungs. Curvature of the spine bones or scoliosis is treated with a brace until surgery is needed to prevent more severe malformations and difficulty with breathing. The treatment for weakness in chewing and swallowing is to introduce alternative feeding methods such as a gastrostomy tube (G tube). The child may eat some foods and swallow some liquids through the mouth but a liquid nutrient supplementation through the “G tube” is needed for the majority of feedings. Exercise in a warm pool (85-90?) called hydrotherapy is relaxing and may be beneficial for muscle movement.

Prognosis

The prognosis depends on the type of SMA and on the individual. Type 1 SMA has the worst prognosis but with new technology the prognosis is improving. At this time the prognosis for those with type 2 SMA varies but survival into early adulthood or later can be expected. People with SMA type 3 can survive longer into adulthood and academic achievements are common. Type 4 SMA, which is the milder form, does not even begin until adulthood therefore the prognosis is the best for type 4. The good news is that research continues to actively search for a cure and better treatments.

Connect with other parents

In the spirit of community and support, Madisons Foundation offers the unique service of connecting parents of children with rare diseases. If you would like to be connected to other parents of children with this disease, please fill out this brief form.

Weblinks

Muscle Dystrophy Association Well written information about SMA with nice pictures. The site also has links to ongoing research.

Families of Spinal Muscular Atrophy
This is a website that has wonderful resources for families that have been affected by this disease. There is news about clinical trials, research and personal stories about patients and families with SMA. It also has information on local chapters, legislative action, annual conferences, message boards, and a kids’ corner.

FightSMA/Andrew’s Buddies
This is a wonderful website dedicated to finding the cure for SMA. With a football legend as their honorary chairman SMA gets a big boost on Capitol Hill. The site also gives current research findings and information about local chapters.

Spinal Muscular Atrophy Foundation
This website is also dedicated to finding a cure and promoting ongoing research on SMA. There is also information on the disease, research updates, and emphasis on raising public awareness about SMA.

Google Search for Spinal Muscular Atrophy (SMA)

References and Sources

1. Muscle Dystrophy Association- www.mdausa.org/publications/fa-sma-qa.html 2. National Institution of Neurological Disorders and Stroke- www.ninds.nih.gov/health_and_medical/disorders/sma.htm 3. Families of Spinal Muscular Atrophy- www.fsma.org This is a website that has wonderful resources for families that have been affected by this disease. There is news about research and personal stories about patients and families with SMA. It also has information on local chapters, legislative action, annual conferences, message boards, and a kids’ corner. 4. FightSMA/Andrew’s Buddies- www.fightsma.com This is a wonderful website dedicated to finding the cure for SMA. With a football legend as their honorary chairman SMA gets a big boost on Capitol Hill. The site also gives current research findings and information about local chapters. 5. Spinal Muscular Atrophy Foundation- www.smafoundation.org/ This website is also dedicated to finding a cure and keeping the name SMA in the government’s mind as more resources are needed for research. There is also information on the disease, research updates, and emphasis on raising public awareness about SMA.