• Posted August 11, 2025

What You Should Know About Spinal Muscular Atrophy (SMA)

Spinal muscular atrophy (SMA) is a genetic neuromuscular disease affecting specialized nerve cells that control voluntary muscle movement, according to the Muscular Dystrophy Association (MDA). It can lead to severe physical disability, paralysis and life-threatening respiratory complications. 

These specialized nerve cells, called neurons, are in the spinal cord and brainstem. As they break down, the muscles they control become progressively weaker, with the damage often beginning in the legs and trunk and then affecting the arms and breathing muscles.

Tragically, SMA is the most common cause of infant death. But thanks to groundbreaking advances in treatments over the past decade, the outlook for people diagnosed with SMA has changed dramatically.

This overview will explore what causes SMA; highlight promising developments in research and clinical care efforts; and showcase how organizations like the MDA support individuals and families affected by the disease across the country.

What is SMA, and how does it happen?

SMA affects an estimated 10,000 to 25,000 people of all ages in the United States, according to the National Institutes of Health. 

It's caused by a mutation in the SMN1 gene, which leads to a deficiency of survival motor neuron (SMN) protein, essential for the health and function of these specialized nerve cells, according to the National Institutes of Neurological Disorders and Stroke (NINDS).

Without enough SMN protein, these nerve cells gradually die, leading to progressive muscle atrophy. The severity of the disease is largely influenced by the number of copies of a related backup gene, SMN2, that a patient has. Generally, the more copies an infant has, the milder the symptoms.

Without treatment, however, even children with less severe forms may develop significant disability over time. 

SMA is commonly categorized into several types based on age of onset and symptom severity: type 0 (prenatal); type I (most severe form, beginning in infancy); type II (chronic form, starting in infancy); type III (chronic form, beginning in childhood); type IV (mildest and rarest form, starts in adulthood); and SMA with respiratory distress (SMARD1).

Most forms of SMA are inherited in an autosomal recessive pattern, meaning a person must inherit two faulty copies of the SMN1 gene, one from each parent, to develop the condition.

While carriers typically show no symptoms, they do possess a single defective copy of the gene and if both parents are carriers, each child has a 25% chance of being affected by SMA.

About 1 in 50 people in the U.S. are estimated to be carriers of a copy of the mutated SMN1 gene, according to Columbia University Irving Medical Center.

Newborn screening and life-saving treatments

Newborn screening for SMA is available nationwide in the United States, thanks to the advocacy from organizations like MDA. This means that most babies with SMA can be identified before symptoms begin.

Early diagnosis allows for treatments to begin earlier, when they have been shown to be the most effective, leading to significantly better motor development outcomes and improved survival.

Since 2016, the U.S. Food and Drug Administration (FDA) has approved three groundbreaking therapies that have dramatically transformed the outlook for individuals with SMA, turning what was once considered a devastating diagnosis into a treatable condition.

• Gene therapy (onasemnogene abeparvovec, marketed as Zolgensma) provides a functional copy of the SMN1 gene directly to motor neurons through a one-time intravenous infusion.

• Antisense oligonucleotide therapy (nusinersen, known as Spinraza) is administered via spinal injection and modifies how the SMN2 backup gene is spliced or processed, enabling it to produce more functional SMN protein.

• SMN2 small molecule splicing modifier therapy (risdiplam, sold as Evrysdi) is an oral medication that enhances SMN protein production from the SMN2 gene, offering a more accessible and non-invasive treatment option for individuals of all ages.

These therapies have collectively saved countless lives and dramatically improved the quality of life of children and adults with SMA.

Many children who would have otherwise faced severe disability or early death are now reaching key developmental milestones, such as sitting, standing, walking and breathing independently.

On the horizon: Next steps in research

While existing SMA therapies have transformed the treatment landscape, researchers and clinicians continue to push the field forward with a focus on improving outcomes across the lifespan. Several promising avenues are now being explored:

Improving drug delivery and access: Efforts are underway to make the most of how current treatments are administered, minimizing invasiveness, lowering how often they are taken, improving their durability and expanding access around the world. For example, Biogen’s DEVOTE study evaluates the impact of higher dose nusinersen to potentially make it more effective and longer-lasting.Meanwhile, the NURTURE study assesses the benefits of initiating nusinersen in presymptomatic individuals, highlighting the importance of early intervention to preserve motor function before symptoms emerge.

Regenerative and restorative approaches: Scientists are investigating ways to repair or regenerate motor neurons and muscle tissue already lost to SMA. This includes stem cell therapies, as well as use of neuroprotective agents and muscle-directed treatments, as reviewed recently in Trends in Molecular Medicine, aimed at strengthening muscle function and restoring mobility in individuals who begin treatment later in life. For instance, Scholar Rock’s apitegromab, a treatment designed to boost muscle strength by blocking a protein called myostatin is under FDA review, with a decision expected by the end of the year.

Combination therapies: Since no single treatment fully addresses every aspect of the disease, combination strategies are becoming a growing focus of research. This includes testing the pairing of gene therapy with muscle-targeted drugs (such as in Genentech’s Hinalea trial) or combining SMN-boosting agents with neuroprotective or anti-inflammatory compounds to achieve a more comprehensive and lasting benefit.

Early-stage Detection and Intervention Strategies: Research is also focused on ever- earlier diagnosis, even before birth as highlighted by a recent clinical study in the New England Journal of Medicine. Advances in prenatal screening, coupled with emerging therapies in the womb, may one day allow intervention before motor neurons begin to degenerate, offering the potential for truly pre-symptomatic care.

Together, these efforts represent the next chapter in SMA care and research.

How MDA is powering progress

For 75 years, MDA has played a pivotal role in advancing the field of neuromuscular disease research, clinical care and advocacy. Scientific progress takes time, but we are now seeing the transformative impact of early research investments come to life.

One powerful example is MDA’s foundational support of Adrian Krainer’s groundbreaking work at Cold Spring Harbor Laboratory, which contributed to the early-stage development of nusinersen (Spinraza), the first approved treatment for SMA. This milestone helped usher in an exciting new therapeutic era for SMA. Thanks in part to MDA’s long-standing leadership, the field continues to make meaningful strides in both treatment options and standards of care for SMA.

Through a multifaceted approach, MDA is accelerating progress on multiple fronts:

Driving innovative research

The MDA Research program has committed more than $50 million to fuel breakthrough science in SMA, including bold, early-stage research in gene editing, advanced delivery systems and next-generation SMN-enhancing strategies. In addition, MDA continues to support research to deepen the understanding of the disease and to discover new treatments that can complement existing gene-targeted therapeutics.

Strengthening care infrastructure

Through its nationwide network of MDA Care Centers, the organization continues to provide individuals and families with access to multidisciplinary care, including early diagnosis, therapeutic guidance, respiratory and nutritional support, as well as coordinated care across specialties.

Empowering families and driving advocacy

MDA Advocacy efforts have helped shape policies that expand access to care and promote early diagnosis, including the advancement of newborn screening for SMA. Meanwhile, the MDA Resource Center offers vital support, connecting and supporting families with care providers, clinical trials and peer networks.

SMA was once a devastating diagnosis with limited options. Today, it’s a condition that can be treated, often from birth, thanks to advances in newborn screening, genetic and small-molecule therapies, and the critical work of organizations like MDA.

With continued research, care and advocacy, there is real hope that everyone living with SMA can enjoy longer, healthier and more independent lives.

About the expert

Brian Lin, PhD,is a Research Portfolio Director at the Muscular Dystrophy Association (MDA), where he oversees research focused on neurology-based diseases within the organization’s portfolio. He earned his PhD from the University of Maryland, Baltimore, studying UBQLN2 mutations in Amyotrophic Lateral Sclerosis (ALS) and Frontotemporal Dementia (FTD). Dr. Lin completed his postdoctoral training at the U.S. Food and Drug Administration (FDA), where his research focused on gene engineering and the role of synonymous mutations in protein therapeutics and gene therapies. His experience bridging molecular research and regulatory science now informs his work at MDA, where he supports cutting-edge research aimed at accelerating treatments and improving outcomes for individuals living with neuromuscular diseases.