Spinal muscular atrophy (SMA) is a neuromuscular disease characterized by degeneration of motor neurons resulting in progressive muscular atrophy (wasting away) and weakness. This weakness is caused by the absence of or defect in the Survival Motor Neuron 1 (SMN1) gene. The reduced level of SMN1 causes the motor neurons to become unhealthy which then causes the muscles to weaken and waste away. Most people have two copies of the gene, one inherited from their mother and one from their father. Carriers of SMA have one normal copy of SMN1 gene and one mutated or defective copy. If the carrier has at least one normal copy of the gene, this allows them to produce enough SMN1 protein to prevent symptoms of the disease so the carrier will not exhibit any symptoms of SMA. The disease usually occurs in children of couples that are both carriers of SMA, each parent having one copy of a normal and one copy of a defective SMN1 gene. There is a 25 percent chance that a child will inherit a defective copy of SMN1 from both parents and will have SMA. The clinical spectrum of SMA ranges from early infant death to normal adult life with only mild weakness.
The most severe form is SMA type I, also referred to as Werdnig-Hoffman disease. Weakness in the lower leg muscles and the shoulder muscles are often the first signs of the disease. Infants born with Type I have very little muscle tone, breathing difficulty, lack of head control, rare spontaneous movement, difficulty sucking or swallowing, legs lying in “frog leg” position, lower than normal birth weight, delays in reaching developmental milestones such as lifting head or sitting up, and progressive weakness. The weakness gets worse over time and eventually will become severe; sensation and the ability to feel are not affected. Intelligence does not appear to be affected; children with SMA are unusually bright and sociable. The majority of children born with SMA are born with Type I, and life expectancy is approximately two years.
Type II, is an intermediate form of SMA. Symptoms usually appear in patients between the age of six and eighteen months, and the progression varies. Infants and children with this form of the disease usually do not ever walk independently, but are able to sit unassisted. Because the progression of symptoms varies, life expectancy ranges from early childhood to adulthood. The majority of Type II patients live into adulthood.
Type III is a mild form of SMA, also known as Kugelberg-Welander or juvenile spinal muscular atrophy. Symptoms typically manifest at eighteen months until early adulthood, and patients with Type III usually have difficulty walking, mild muscle weakness, and are at an increased risk for respiratory infections. Patients with this form of the disease have a normal life expectancy.
Type IV is the adult form of SMA. This is a less common form of SMA that usually emerges in adults after the age of 35. Type IV is characterized by a very slow progression of symptoms that particularly affects the ability to walk.
Diagnostic testing for SMA includes a thorough health history and extensive neurologic examination. In order to be diagnosed with SMA symptoms need to be present. The health care provider will assess for a family history of neuromuscular disease, flaccid (floppy) muscles, absence of deep tendon reflexes, and twitching of tongue muscles. Lab and imaging testing may include: increased CPK levels, this is an enzyme found mainly in the heart, brain, and skeletal muscle, DNA testing to confirm diagnosis, Electromyography, a test that will check the health of the muscles as well as the nerves that control the muscles, an extensive x-ray of the spine (MRI), and a muscle biopsy, this entails removing a small piece of muscle tissue for examination. The most common form of SMA is caused by mutations of the SMN1 gene therefore in most cases a diagnosis can be made by the SMN gene test. This is a simple blood test that identifies mutations and deletions of the SMN1 gene used to make the SMA diagnosis.
There is no treatment for the progressive weakness caused by the disease therefore, supportive care is critical. The most important step is to confirm the diagnosis of SMA through diagnostic studies mentioned above. Breathing complications are common such as respiratory infections and aspiration (breathing in a foreign object), because people affected with SMA have difficulty protecting their airway, managing the affected person’s airway is critical. Physical and Occupational therapy are important to prevent contractions of the muscles and tendons and to prevent abnormal curvature of the spine (scoliosis). An exercise regimen should be instituted daily and bracing may become necessary. Proper nutrition is another important aspect of managing the disease. Children with SMA are prone to over- and under- nutrition problems, so an individualized nutrition plan is recommended. Another important point of managing the disease is to prepare for the illness. Encourage the family to plan for medical emergencies and to share their plan with the medical professionals involved in the patient’s care.
Early diagnosis is a key component so that supportive care can be started immediately. Call your health care provider if a child appears weak, has difficulty feeding or breathing, or develops other symptoms of SMA. Prospective parents with a family history of SMA should consider genetic counseling to explore the incidence of producing a child with the disease. Individuals and couples considering carrier screening for SMA may want to discuss their risk with a genetic counselor. Genetic counselors in your area can be located through the National Society of Genetic Counselors website, or log on to www.smafoundation.org
The Women’s Health Task Force of Clearfield County meets the first Thursday of each month. The next meeting is August 4, noon, at the Children’s Aid Society, 1008 South 2nd St. in Clearfield. All interested persons are invited to participate.
Joann Graham, RN
HealthSouth Nittany Valley Nurse Liaison