Diagnosing Spinal Muscular Atrophy

SMA is diagnosed primarily through a blood test, which looks for the presence or absence of the SMN1 gene, in conjunction with a suggestive history and physical examination. Normally, individuals have two genes called Survival Motor Neuron 1 and 2. In approximately 95% of patients with SMA there is an absence of the SMN gene sequence, which is present in normal individuals. Sometimes the SMN1 gene is not missing, but mutated. The numbers of copies of SMN2, a near identical backup copy of the SMN1 gene, is related to the severity of the disease, but does not reliably predict a specific SMA type in a given individual. SMA type is generally determined from the clinical examination evaluating the child's degree of weakness and ability to achieve major motor milestones such as sitting independently or walking. Occasionally, doctors may request muscle biopsy or EMG (electromyography) testing. Since the genetic blood test became available, a muscle biopsy is almost never indicated and is valuable mainly in cases where the blood DNA test is negative. EMG measures the electrical activity of muscle. Sometimes this test is performed to help distinguish other disorders of nerve or muscle, which can mimic SMA. Small recording electrodes (needles) are inserted into the patient's muscles, usually the arms and thighs, while an electrical pattern is observed and recorded. In addition, a nerve conduction velocity test (NCV) is performed to help assess how well the nerves are functioning in response to an electrical stimulus. Small shocks are repeatedly administered to help assess nerve integrity and function. When performing this test on a child, if at all possible, a doctor experienced in caring for children should perform it.

Prognosis ... What Does it Mean? What Are We to Expect?

Researchers have identified the SMN1 gene as the primary manufacturer of the SMN Protein. It is the absence/defect of this SMN1 gene that causes Spinal Muscular Atrophy. However, there is another form of this gene called SMN2. The SMN2 gene is similar to SMN1, but does not produce as much protein, or the right kind of protein, as the SMN1 gene. One determination of prognosis is the number of copies of the SMN2 gene. The greater the number of SMN2 copies, the more SMN protein is produced and the greater likelihood that more motor neurons remain healthy and productive. Individuals with only 1 or 2 copies of the SMN2 gene will typically have the most severe expressions of SMA. Three or more copies of the SMN2 gene will typically mean a less severe expression.

Each type of SMA has variability among individual patients. Please keep this in mind when considering an individual's care. Raising a child with SMA should be no different than raising a child who is not affected. Do as many things as possible that are age appropriate. Many times this means making adaptations. It is very important that children with SMA are assisted in reaching their utmost potential.

It is important to understand that parents and patients have rights and that you are not alone. Most hospitals have social service departments that can give you a shoulder to lean on. Don't be afraid to say NO if something doesn't seem right. Don't be intimidated or afraid to ask questions. If you forget to ask something, call your doctor or contact Families of SMA for suggestions. In this context, it is also important that a physician who is familiar with SMA and its complications follow your child.

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