A 24-Year Mortality Analysis of Spinal Muscular Atrophy and a Blueprint for Future Pediatric Care

For generations of pediatricians, neonatologists, and pediatric neurologists, a diagnosis of Spinal Muscular Atrophy (SMA) Type 1 carried an unspoken, devastating finality. Historically categorized as one of the most common genetic causes of infant mortality, the disease progression was aggressively predictable: a progressive loss of alpha motor neurons leading to profound muscle wasting, respiratory failure, and, in the vast majority of cases, death before the age of two.

However, the introduction of targeted, gene-modifying therapies over the past decade has fundamentally disrupted this trajectory. To map the large-scale, population-level impact of these breakthroughs, a recent landmark study published in Neurology Open Access (2026), titled “Trends in Spinal Muscular Atrophy-Related Mortality in Children in the United States, 1999–2023,” analyzed 24 years of public health data. Utilizing data from the Centers for Disease Control and Prevention Wide-ranging Online Data for Epidemiologic Research (CDC WONDER) database, the researchers conducted a comprehensive Joinpoint regression analysis to chart age-adjusted mortality rates (AAMRs) among infants and children aged four and younger.

For healthcare providers, this paper provides more than just a historical retrospective; it establishes a new baseline for clinical practice.

Why It Matters

Overview of Spinal Muscular Atrophy

Spinal muscular atrophy is an autosomal recessive neurodegenerative disorder caused by homozygous mutations or deletions in the SMN1 gene, resulting in a deficiency of the survival motor neuron (SMN) protein and the subsequent loss of anterior horn cells. The disease is a leading genetic cause of infant mortality, with a pan-ethnic incidence of 1 in 11,000 live births. The pediatric spectrum of SMA is primarily classified into four types based on age of onset and maximum motor milestones achieved, which inversely correlate with the copy number of the hypomorphic SMN2 modifier gene:

1. Type 0: Prenatal onset characterized by severe hypotonia, areflexia, joint contractures, and early respiratory failure, typically leading to death within the first six months of life.
2. Type 1 (Werdnig-Hoffman Disease): Onset before six months; infants present with profound symmetric proximal weakness, poor head control, areflexia, tongue fasciculations, and a bell-shaped chest from paradoxical “belly-breathing”. Patients never achieve independent sitting and historically progress to respiratory failure before age two.
3. Type 2: Onset before 18 months; children achieve the ability to sit unassisted but never walk independently. They face severe orthopedic complications, including joint contractures and progressive scoliosis, which can cause restrictive lung disease.
4. Type 3 (Kugelberg-Welander Disease): Onset after 18 months; pediatric patients achieve independent ambulation. They present with proximal limb weakness but are mostly spared severe scoliosis or respiratory compromise, retaining a normal life expectancy. Cognition remains completely normal across all childhood types. Standard management requires an aggressive, multidisciplinary approach involving proactive non-invasive ventilation, assisted airway clearance, nutritional support via early gastrostomy, and orthopedic stretching or bracing.

Quantifying a Therapeutic Revolution

This study is highly significant because it provides objective, nationwide validation of how rapidly a population’s mortality risk can change when advanced molecular therapeutics are translated into real-world clinical practice. While clinical trials originally demonstrated the efficacy of individual drugs, this paper captures the macro-level shift, tracking a dramatic paradigm change from pure supportive care to successful disease modification across the entire United States.

The study analyzed a total of 2,191 SMA-related deaths over more than two decades, revealing a structural shift that occurred in three distinct temporal phases:

• The Baseline Decline (1999–2016): Long before targeted therapies reached the market, the baseline SMA-related AAMR was already experiencing a slow, steady decrease, dropping from 7.64 per 1,000,000 children in 1999 to 4.7 per 1,000,000 in 2016. This initial annualized percent change (APC) of 2.08% reflects gradual, historical improvements in standard supportive care. The proactive introduction of non-invasive positive pressure ventilation (NIPPV), aggressive nutritional support via gastrostomy tubes, and optimized airway clearance protocols allowed vulnerable infants to survive longer, even without targeted molecular interventions.
• The Accelerated Drop (2016–2018): Between 2016 and 2018, the steady decline turned into a sharp drop. The AAMR plummeted from 4.7 to 1.54 per 1,000,000 population. This represents an unprecedented drop of 43.43% in just two years. This sudden shift directly coincides with the late-2016 FDA approval and subsequent rapid adoption of nusinersen, the first intrathecal antisense oligonucleotide designed to enhance the inclusion of exon 7 in SMN2 pre-mRNA transcription. Clinicians rapidly implemented this drug to treat and rescue the most vulnerable infants with SMA Type 1, immediately altering national survival curves.
• The Contemporary Plateau (2018–2023): Following this sharp decline, the mortality rate entered a stable plateau phase from 2018 to 2023, shifting from 1.54 to 1.22 per 1,000,000 (APC= -3.53%). Remarkably, this stabilization occurred despite the introduction of two more advanced therapies: the one-time intravenous gene replacement therapy onasemnogene abeparvovec (approved in 2019) and the oral small molecule risdiplam (approved in 2020).

Understanding the Therapeutic Plateau

For providers, this plateau is a crucial point of analysis. Why did mortality rates stabilize instead of continuing their rapid downward trajectory after two more highly effective drugs were introduced? The authors point to a “steady state” phenomenon in treatment, alongside substantial, ongoing barriers to equitable care.

These barriers include exceptionally high upfront medication costs, strict prior authorization demands from insurance payers, and a lack of local access to specialized tertiary pediatric neuromuscular centers. When medication access is delayed or denied during the critical early weeks of life, irreversible motor neuron loss occurs, preventing some infants from fully benefiting from these lifesaving treatments.

Who It Affects

Analyzing Patient Demographics and Regional Realities

To optimize clinical monitoring and screening protocols, providers must clearly understand the demographic distribution of the population affected by SMA. Across the 24-year study window, the baseline demographic characteristics of the 2,191 recorded pediatric deaths showed a relatively balanced distribution by sex, though geographic variances in mortality burden were more pronounced.

Biological Sex and Geographic Distribution

• Sex Distribution: The study sample consisted of 1,184 male patients (54%) and 1,007 female patients (46%). When the researchers executed a secondary analysis stratifying the mortality rates by sex over time, they noted identical downward trends across both groups, confirming that the benefits of therapeutic advancements have been shared equally by both male and female children.
• Regional Imbalances: When looking at the raw numbers across geographic areas, the Southern region of the United States consistently bore the highest absolute burden of SMA-related deaths during both the pre-treatment era (1999–2017) and the modern treatment era (2018–2023). As illustrated in the study’s regional mapping, the South recorded 716 deaths in the early era and 71 deaths in the later era—substantially outnumbering the Northeast, Midwest, and West.

While the entire country saw a substantial absolute decrease in mortality, the South’s higher numbers underscore the ongoing need to address regional public health disparities. These disparities may stem from varying state-by-state timelines for adopting universal newborn screening, localized pockets of poverty, and uneven access to comprehensive pediatric subspecialty care.

Methodological Note on Data Stratification

The authors noted a key limitation: they could not perform deeper, cross-sectional stratifications by specific racial/ethnic groups or individual states. This restriction was due to the CDC WONDER data use agreement, which flags mortality counts under 20 as statistically unreliable to protect patient privacy. Consequently, hidden healthcare disparities within smaller sub-populations may remain unmeasured.

What Changes

A New Multidisciplinary Care Paradigm

The clear takeaway from this 24-year analysis is that SMA is no longer a uniformly lethal disease of early infancy. Because these children are surviving at unprecedented rates, the traditional model of reactive, palliative care must be completely replaced by an active, long-term, multidisciplinary management strategy.

Shift in Care from Pediatric to Complex Multi-System Management

Survival motor neuron (SMN) protein is expressed ubiquitously throughout human tissue, and its chronic deficiency impacts systems well beyond the neuromuscular junction. As patients live longer, care requirements are shifting toward managing a complex, multi-system disorder:

• Pivotal Role of Pulmonary Care: Although advanced therapeutics preserve bulbar and diaphragmatic function, respiratory vulnerability remains a major driver of clinical care. Continuous sleep diagnostics, proactive airway clearance regimens, and targeted non-invasive ventilation continue to be essential components of long-term care to prevent recurrent nocturnal hypoventilation and aspiration pneumonia.
• Multidisciplinary Infrastructure: Managing the modern SMA patient requires close coordination among primary care providers and a diverse team of specialists, including pediatric neurologists, pulmonologists, nutritionists, gastroenterologists, orthopedic surgeons, and physical/occupational therapists. Orthopedic monitoring is especially critical, as increased survival often brings progressive scoliosis and joint contractures that require timely intervention.
• Transition of Care Programs: Historically, adult neurologists rarely encountered SMA Type 1. Today, health systems must design structured transition-of-care pipelines. Moving patients smoothly from pediatric to adult specialized neurology clinics ensures that therapeutic schedules, spinal monitoring, and complex physical therapy routines remain uninterrupted during adolescence and early adulthood.

The Imperative of Presymptomatic Newborn Screening

The dramatic drop in mortality documented between 2016 and 2018 underscores a fundamental clinical principle of neurodegeneration: time is motor cortex. Once alpha motor neurons undergo apoptotic degeneration, they cannot be recovered.

To achieve optimal outcomes, disease-modifying therapies must be delivered during the presymptomatic phase—before clinical weakness or fasciculations appear. This reality places an important responsibility on primary care providers and public health systems to champion universal newborn screening (NBS) across all jurisdictions, ensuring that every infant is screened and genotyped within the first days of life.

Bridging the Gap Between Innovation and Access

The 24-year retrospective from Al-Salahat and colleagues provides definitive, national proof of the success of modern genetic therapies. The 43.43% reduction in child mortality that followed the introduction of targeted molecular treatments is an extraordinary achievement in modern medicine.

Yet, the plateau observed from 2018 to 2023 serves as a clear warning that scientific innovation alone is not enough. As clinicians, our responsibilities extend beyond the clinic doors; we must actively advocate for the removal of structural barriers to care. Supporting universal newborn screening, demanding streamlined insurance authorization pathways, and fighting for equitable access to specialized care centers are essential steps to ensure that these lifesaving advancements reach every child who needs them.

References

1. Kolb SJ, Kissel JT. Spinal Muscular Atrophy. Neurol Clin. 2015;33(4):831-846. doi:10.1016/j.ncl.2015.07.004
2. Al-Salahat A, Bin Abdul Jabbar A, Danielson L, Chen YT, Bernitsas E, Koh S. Trends in Spinal Muscular Atrophy-Related Mortality in Children in the United States, 1999–2023. Neurol Open Access 2026;2:e000060. doi:10.1212/WN9.0000000000000060.