What is Spinal Muscular Atrophy?
Spinal muscular atrophy (SMA) is a disorder that degrades the central nervous system, caused by a mutation in the survival motor neuron (SMN) on the 5th chromosome. The mutation causes muscles to not receive signals from the nerve cell located in the spinal cord that controls voluntary muscle movement. This ultimately leads to your body continuously becoming weaker, which may result in a decrease in daily activities such as breathing, swallowing, eating, and walking.
SMA has five subtypes from 0 to 4 based on the age at the onset of symptoms. SMA type 0, which is rare, begins prior to birth and is the most severe. SMA type 1 is the most common type, with symptoms typically appearing before 6 months of age. Onset of SMA type 2 is often between 3 and 15 months of age and less severe than type 1. SMA type 3 has a more varied age of onset, ranging between 18 months and adulthood. Type 4 SMA is a rare, mild form of SMA, which may be diagnosed in late adolescence or adulthood.
How common is Spinal Muscular Atrophy?
SMA affects approximately 1 in 11,000 births in the U.S., and about 1 in every 50 Americans is a genetic carrier.1 A pan-ethnic study in 2012 found that carrier frequency in North America was highest in white individuals (1 in 47) and lowest in Hispanic individuals (1 in 68) and Black individuals (1 in 72).2
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SMA symptoms can vary from mild to severe based on subtype. The primary symptom of SMA is muscle weakness, which can lead to a person needing assistance with daily tasks such as cleaning, walking, eating, and driving. The muscles that are most affected are those closest to the center of the body. These muscles include those of the shoulders, hips, thighs, and upper back. The lower limbs seem to be affected more than the upper limbs, and deep tendon reflexes are decreased. Other symptoms can include gastrointestinal symptoms, such as gastroesophageal reflux and poor bowel motility or constipation.
How is Spinal Muscular Atrophy diagnosed?2
Newborn screening for SMA is being implemented throughout the United States and is currently conducted in 48 states. If the patient is already born, SMA should be suspected in any infant with unexplained weakness or hypotonia. To diagnose SMA, genetic testing is utilized to detect mutations in the SMN1 gene.
Carrier testing for SMA is also available using a molecular genetic test to identify the most common SMN1 mutation associated with SMA.
Financing Your Care
Financial assistance coordination may be available to help with your medication costs, including manufacturer and community programs. Accredo representatives are available to help find a program that may work for you.
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There are many organizations that support research and advocacy for Spinal Muscular Atrophy. See below for a few of those organizations.
Spinal Muscular Atrophy Organizations
Meet the Team
Accredo’s Spinal Muscular Atrophy care team is dedicated to serving you and we understand the complexity of your condition. Our specialty-trained clinicians are available from 8am to 11pm Monday through Friday and Saturday 8am to 5pm Eastern Standard Time, to answer any questions. You can reach the Spinal Muscular Atrophy dedicated care team at
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