Spinal muscular atrophy, commonly called SMA, is a rare genetic neuromuscular condition. It primarily affects the motor neurons that control voluntary muscle movement. As these nerve cells become damaged or are lost, the muscles they control become weak and may gradually decrease in size.
SMA Awareness Month is an opportunity to help families understand the condition, recognize why newborn screening matters and learn how treatment has changed the outlook for many children. SMA is not caused by anything a parent did during pregnancy, and it cannot be prevented through diet, exercise or prenatal lifestyle choices.
What causes spinal muscular atrophy?
Most cases are caused by changes in a gene called survival motor neuron 1, or SMN1. This gene normally provides instructions for producing survival motor neuron protein, commonly called SMN protein. Motor neurons need this protein to remain healthy and function properly.
When a child does not produce enough functional SMN protein, motor neurons in the brainstem and spinal cord begin to deteriorate. Because these nerve cells send movement signals to muscles, their loss causes progressive muscle weakness and muscle wasting.
A second gene, SMN2, produces a smaller amount of functional SMN protein. The number of SMN2 copies a person has often influences the severity of SMA, although it cannot predict an individual child’s course with complete accuracy. In general, having more SMN2 copies is associated with a less severe presentation.
Myth: “SMA is a form of muscular dystrophy.”
Fact: SMA and muscular dystrophy can both cause muscle weakness, but they are not the same condition.
In SMA, the primary problem begins with the motor neurons that communicate with the muscles. In many muscular dystrophies, the disease primarily affects the muscle tissue itself.
The distinction matters because the genetic causes, patterns of progression and available treatments are different. A physical examination alone may not determine the exact cause of a child’s weakness, which is why genetic and other diagnostic testing can be important.
How is SMA inherited?
The most common form of SMA is inherited in an autosomal recessive pattern. A child generally must inherit two nonworking copies of the SMN1 gene—typically one from each parent—to develop the condition.
A person who has one working copy and one nonworking copy is called a carrier. Carriers usually do not have SMA symptoms because the working copy produces enough SMN protein for normal motor-neuron function.
When both parents are carriers, each pregnancy has a 25% chance of resulting in a child with SMA, a 50% chance of resulting in a child who is an unaffected carrier and a 25% chance of resulting in a child who neither has SMA nor carries the familial gene change. These probabilities begin again with every pregnancy; previous pregnancy outcomes do not change the odds for the next child.
In a small number of cases, a new genetic change or another uncommon genetic pattern may be involved. Genetic counseling can help families understand test results, recurrence risks and reproductive options.
Myth: “If SMA does not run in the family, a baby cannot have it.”
Fact: SMA can occur without any known family history.
Carriers generally have no symptoms and may not know they carry an SMN1 change. A child may therefore be the first person in the family diagnosed with SMA, even though the genetic changes were inherited.
Carrier screening can identify many people who carry an SMN1 gene change, but no carrier test detects every possible genetic pattern. Families with a known history of SMA or an abnormal screening result should discuss the limitations and meaning of testing with a genetic counselor or physician.
Why newborn screening matters
Newborn screening can identify many infants with SMA before weakness or other symptoms are apparent. The screening is performed using the small blood sample collected from a baby’s heel shortly after birth.
SMA was added to the federal Recommended Uniform Screening Panel in 2018. All 50 states now screen newborns for the most common genetic cause of SMA, although state programs and follow-up processes can vary.
An out-of-range newborn screen is not, by itself, a final diagnosis. It means that confirmatory genetic testing and specialist evaluation are needed. Follow-up should occur promptly, even if the baby appears strong and healthy.
Newborn screening does not identify every rare SMN1 variant or every condition that can cause muscle weakness. A child with concerning symptoms still needs evaluation even if the newborn screen was reported as normal.
Why is early treatment so important?
Motor neurons that have already been lost cannot simply be restored. Disease-modifying treatment is therefore generally most effective when it begins before significant motor-neuron loss occurs.
Studies of babies treated before symptoms developed have shown substantially better motor outcomes than the historical course of untreated SMA. Many presymptomatically treated children have achieved milestones such as sitting, standing or walking that would not have been expected based on the traditional form of SMA predicted at diagnosis.
Early treatment does not guarantee a symptom-free outcome for every child. Results can vary based on the genetic profile, timing of treatment, treatment selected and other individual factors. However, the availability of effective treatment is the central reason SMA was added to newborn-screening programs.
What are the possible signs of SMA?
Symptoms vary widely in their age of onset and severity. In infants, possible signs include low muscle tone, limited spontaneous movement, difficulty holding up the head, weak crying, a weak cough or difficulty sucking and swallowing. Some babies have a “frog-leg” posture, in which the hips and knees rest outward because of muscle weakness.
Older children may have delayed motor milestones, difficulty sitting without support, trouble standing or walking, frequent falls, difficulty climbing stairs or trouble getting up from the floor. A tremor of the fingers, progressive weakness closer to the center of the body and loss of previously acquired motor abilities may also occur.
Breathing muscles can be affected. Children may have a weak cough, difficulty clearing respiratory secretions, repeated chest infections or breathing that relies heavily on the abdominal muscles.
These signs are not unique to SMA. Many more common conditions can cause delayed milestones, low muscle tone or weakness. Parents should not attempt to diagnose SMA based on symptoms alone, but persistent or progressive weakness deserves medical evaluation.
Myth: “A child with SMA has intellectual or learning impairment.”
Fact: SMA primarily affects motor function, not intelligence.
Children with SMA can think, learn, communicate and form relationships. Physical limitations should not be mistaken for cognitive limitations. A child who cannot point, sit, write by hand or speak loudly may still fully understand what is being said.
Some children benefit from communication devices, adapted computers, mobility equipment or other assistive technology. These tools support independence and access; they do not indicate reduced intelligence.
School accommodations may be needed for mobility, fatigue, physical access, emergency planning or assistance with written work. Expectations for learning should be based on the individual child’s abilities rather than assumptions about the diagnosis.
Are there different types of SMA?
SMA has historically been categorized into types based on the age symptoms begin and the highest motor milestone achieved without treatment.
Type 0 begins before birth and is the most severe. Type 1 usually becomes apparent during the first six months of life, and affected infants historically did not achieve independent sitting. Type 2 generally begins between approximately 6 and 18 months, with children able to sit but not independently walk. Type 3 begins after 18 months, and affected children achieve independent walking but may later experience increasing weakness. Type 4 begins in adulthood and is usually the mildest form.
These categories describe the historical untreated course of SMA. They are becoming less precise in children identified through newborn screening and treated before symptoms develop. Physicians increasingly consider a child’s genetic findings, age at treatment, current motor abilities, breathing and swallowing function rather than relying only on a traditional type number.
How is SMA diagnosed?
Genetic testing can confirm most cases by identifying changes in the SMN1 gene. Testing often also measures the number of SMN2 copies because that information may help guide treatment decisions and discussions about the likely disease course.
A pediatric neurologist or neuromuscular specialist may evaluate the child’s strength, muscle tone, reflexes, breathing, swallowing and motor development. Electromyography, nerve-conduction testing or other studies may occasionally be needed when genetic results are unclear or another condition is being considered.
After an out-of-range newborn screen, confirmatory testing and referral should not be delayed while waiting for symptoms.
How is SMA treated?
There are now several FDA-approved disease-modifying treatments for SMA. They work in different ways to increase the amount of functional SMN protein or address the underlying genetic defect.
Nusinersen, sold as Spinraza, modifies the way the SMN2 gene is processed so it produces more functional SMN protein. It is delivered into the fluid surrounding the spinal cord through repeated intrathecal injections and is approved for pediatric and adult patients.
Risdiplam, sold as Evrysdi, also changes SMN2 processing to increase functional SMN protein. It is taken by mouth and is approved for patients with SMA who are 2 months of age and older.
Onasemnogene abeparvovec-xioi, sold as Zolgensma, is a one-time intravenous gene therapy that delivers a working copy of the SMN gene. It is approved for children younger than 2 years with SMA caused by changes in both copies of SMN1. The treatment can cause serious liver injury and requires medication and laboratory monitoring before and after infusion.
In 2025, the FDA also approved Itvisma, an intrathecally administered formulation of onasemnogene abeparvovec, for pediatric and adult patients age 2 and older with a confirmed SMN1 mutation. It is delivered as a one-time injection into the fluid surrounding the spinal cord and also requires careful medical screening and follow-up.
The appropriate treatment depends on factors including the child’s age, symptoms, genetic findings, previous treatment, liver health and other medical considerations. These medications have different risks, monitoring requirements and eligibility criteria.
Myth: “Gene therapy cures SMA.”
Fact: Gene therapy can change the course of SMA, but it is not accurate to promise a complete cure.
Gene therapy supplies genetic instructions that allow cells to produce needed SMN protein. It cannot reliably replace motor neurons that have already been lost or reverse every established complication.
Some children treated very early achieve age-appropriate or near-age-appropriate development, while others continue to have weakness or require respiratory, nutritional, orthopedic or mobility support. Long-term monitoring remains necessary after gene therapy, even when a child is doing well.
Treatment includes more than medication
Disease-modifying therapy is only one part of SMA care. Children may also need physical therapy, occupational therapy, respiratory care, nutritional support, orthopedic monitoring, mobility equipment and assistance with swallowing or communication.
Physical and occupational therapy can help maintain flexibility, support comfortable positioning, prevent contractures and maximize safe participation. Therapy should be adapted to the child’s strength and endurance. Exercise cannot repair the genetic change or replace medical treatment, and excessive fatigue may be counterproductive.
Respiratory care may include cough-assistance techniques, secretion management, noninvasive ventilation or other support. Swallowing and nutrition should be monitored because weakness can increase the risk of choking, aspiration or inadequate growth.
Scoliosis, hip problems and joint contractures can develop as a result of muscle weakness. Orthopedic monitoring allows these concerns to be identified and managed appropriately.
Myth: “Children with SMA should avoid physical activity.”
Fact: Children with SMA should have opportunities for safe, individualized movement and recreation.
Appropriate physical activity can support flexibility, circulation, emotional health and participation. The safest type and intensity depend on the child’s strength, breathing function and orthopedic health.
Swimming, adaptive sports, assisted movement and accessible recreation may be options for some children. A physical therapist or neuromuscular care team can help families balance activity with rest and avoid overwork or injury.
Mobility devices should not be viewed as giving up. A stroller, walker or power wheelchair can conserve energy, increase independence and allow a child to participate more fully at school and in the community.
Supporting the whole child and family
SMA care often involves a team that may include a pediatrician, neurologist, pulmonologist, physical therapist, occupational therapist, dietitian, speech or feeding specialist, orthopedic physician, genetic counselor and social worker.
Families may also need support navigating insurance, home equipment, school accommodations, transportation and emotional stress. Siblings can have questions or worries and may benefit from age-appropriate explanations.
Children with SMA should be included in decisions about their care as developmentally appropriate. They should also be encouraged to pursue friendships, education, recreation and personal interests rather than being defined solely by their diagnosis.
When should parents seek evaluation?
Parents should speak with their child’s pediatrician about persistent low muscle tone, delayed motor milestones, progressive weakness, loss of previously acquired abilities, frequent falls or difficulty swallowing.
Urgent medical evaluation is needed when a baby or child has breathing difficulty, a weak or ineffective cough during illness, bluish discoloration, repeated choking, signs of dehydration or unusual sleepiness.
An out-of-range newborn screening result requires prompt confirmatory testing and specialist follow-up, even if the baby has no visible symptoms.
Awareness has become action
The outlook for SMA has changed significantly since the first disease-modifying treatment was approved in 2016. Newborn screening allows many infants to be identified before symptoms, and available treatments can preserve motor function, improve milestone achievement and extend survival.
SMA remains a serious, lifelong condition, and outcomes are not identical for every child. Awareness matters because early identification and treatment can make a meaningful difference.
Parents who receive an abnormal newborn-screening result or notice progressive weakness should not be expected to determine the diagnosis alone. Prompt evaluation by a pediatric neuromuscular team provides the clearest path to confirmatory testing, timely treatment and coordinated support.