What is the average lifespan of someone with SMA?

Did you know that the lifespan of someone with Spinal Muscular Atrophy (SMA) depends heavily on the type and severity of the condition? Understanding what is the average lifespan of someone with SMA requires looking at specific factors, as new treatments are transforming the prognosis for many patients.

Quick Summary

The lifespan for an individual with SMA depends on the specific type, which ranges from severe forms with a significantly shortened life expectancy to milder types that typically do not affect lifespan due to targeted therapies.

Key Points

• SMA lifespan varies widely: Life expectancy is not a single number but depends heavily on the specific SMA type, from severe infantile-onset to milder adult-onset forms.

• New treatments have changed outcomes: The introduction of disease-modifying therapies (DMTs) has dramatically improved the prognosis for individuals with SMA, especially those with Type 1 and Type 2.

• Early intervention is crucial: Starting treatment as early as possible, ideally before symptoms appear, leads to the best outcomes and can extend lifespan.

• Prognosis depends on genetic factors: The number of copies of the SMN2 gene influences disease severity; more copies generally lead to milder symptoms.

• Supportive care is vital: In addition to targeted therapies, managing respiratory, nutritional, and musculoskeletal complications is key to a better quality of life and longevity.

• Milder types have a normal lifespan: Individuals with Type 3 and Type 4 SMA generally have a normal life expectancy, although they may experience progressive muscle weakness.

Understanding the Spectrum of SMA

Spinal Muscular Atrophy (SMA) is a genetic disease that damages and kills motor neurons, leading to progressive muscle weakness and atrophy. The average lifespan is not a fixed figure but is dependent on several factors, most significantly the type of SMA, which is primarily classified by age of onset and maximum motor function achieved.

SMA Type 1: The Most Severe Form

Traditionally known as Werdnig-Hoffmann disease, this is the most common and severe form of SMA, with symptoms appearing before 6 months of age. Infants with Type 1 experience severe muscle weakness, trouble swallowing, and significant respiratory distress. Without treatment, the life expectancy for these children was historically less than two years, with respiratory failure being the leading cause of death. However, the advent of new therapies has dramatically changed this prognosis, extending and improving the quality of life for many patients.

SMA Type 2: The Intermediate Form

Also known as Dubowitz disease, Type 2 SMA symptoms emerge between 6 and 18 months. Children with this type can often sit without support but cannot stand or walk independently. Before modern treatments, about 70% of individuals with Type 2 SMA survived into their twenties, with some living into their 30s. With proactive respiratory care and disease-modifying therapies, life expectancy is now being extended into adulthood for many.

SMA Type 3: The Milder Childhood Form

Symptoms of Type 3 SMA, also called Kugelberg-Welander disease, appear after 18 months of age and sometimes as late as adolescence. Individuals with this form are able to walk at some point, although they may eventually require a wheelchair due to progressive muscle weakness. Respiratory problems are usually minimal, and life expectancy is typically not affected. However, managing mobility and other complications is a lifelong process.

SMA Type 4: Adult-Onset

This is the mildest and rarest form of SMA, with symptoms appearing in adulthood, typically after age 21. The muscle weakness and tremors are usually mild to moderate and progress very slowly. For individuals with Type 4 SMA, life expectancy is not impacted, and they generally remain mobile throughout their lives, though some may need assistive devices later on.

How New Treatments Are Changing the Prognosis

The traditional understanding of SMA prognosis has been reshaped by recent advancements in disease-modifying therapies (DMTs). These treatments, when initiated early, are proving to be highly effective in slowing or halting disease progression, especially in the more severe types.

1. Nusinersen (Spinraza): The first approved SMA treatment, this is an antisense oligonucleotide that increases the production of the SMN protein, which is vital for motor neuron survival. It is administered via intrathecal injection and is approved for all SMA types.
2. Onasemnogene abeparvovec (Zolgensma): A gene therapy approved for children under two years old with SMA, Zolgensma provides a functional copy of the missing SMN1 gene. It is a one-time intravenous infusion designed to halt the progression of the disease.
3. Risdiplam (Evrysdi): This oral medication works similarly to Nusinersen by increasing the SMN protein. Approved for patients as young as two months, it offers a non-invasive treatment option.

These therapies are fundamentally altering outcomes, allowing children with Type 1 SMA to survive longer and achieve motor milestones previously considered impossible.

Factors That Influence Life Expectancy

Beyond the specific SMA type and availability of treatment, several factors influence an individual's prognosis:

• Age of Onset: Earlier symptom onset is correlated with a more severe disease course and shorter survival.
• SMN2 Copy Number: The SMN2 gene acts as a backup for the mutated SMN1 gene, producing a small amount of functional SMN protein. A higher number of SMN2 gene copies generally correlates with a milder disease presentation and a more positive prognosis.
• Proactive Supportive Care: Comprehensive care, including respiratory support, nutritional management, and physical therapy, is crucial for managing complications and improving quality of life across all types of SMA.
• Genetic Modifiers: Other less common genetic modifiers can also influence the outcome of SMA.

Managing Symptoms to Maximize Quality of Life

While new treatments focus on the root genetic cause, proactive supportive care remains essential for managing symptoms and preventing complications. This includes a multidisciplinary approach involving:

• Pulmonology: Managing respiratory function is paramount, especially for Types 1 and 2, and may involve non-invasive ventilation or cough-assist devices.
• Physical and Occupational Therapy: These therapies help with mobility, joint flexibility, and energy conservation, which are vital for maintaining function.
• Orthopedic Care: Conditions like scoliosis are common in SMA and require monitoring and, in some cases, surgical intervention.
• Nutrition: Ensuring adequate nutrition, sometimes with the assistance of a feeding tube, is critical for maintaining overall health.

SMA Life Expectancy Comparison

SMA Type	Age of Onset	Pre-Treatment Lifespan	Post-Treatment Outlook
Type 0	Before or at birth	Weeks to a few months	Possibly prolonged, but outcomes unclear
Type 1	Under 6 months	Less than 2 years	Significantly improved; many reaching milestones and extended survival
Type 2	6 to 18 months	Into adulthood (often 20s-30s)	Extended and improved quality of life
Type 3	After 18 months	Normal life expectancy	Normal life expectancy, improved mobility management
Type 4	Adulthood (age 21+)	Normal life expectancy	Normal life expectancy, symptom progression slowed

Conclusion

Determining what is the average lifespan of someone with SMA is a complex question with a nuanced answer that depends on the individual's specific type of SMA. While historical data paints a grim picture for the more severe forms, the landscape of SMA prognosis is evolving rapidly due to revolutionary treatments. These therapies, coupled with comprehensive supportive care, are enabling individuals with SMA to live longer, fuller lives than ever before. This shift highlights the importance of early diagnosis through newborn screening and prompt access to care, offering renewed hope for individuals and families impacted by this condition.

For additional information and support, you can visit Cure SMA.

Frequently Asked Questions

What is the primary factor influencing SMA lifespan?

The primary factor influencing SMA lifespan is the specific type of SMA an individual has. The four main types (1, 2, 3, and 4) are categorized by the age of onset and severity, and they have drastically different impacts on longevity.

Did SMA treatments exist before recently?

Before recent advancements in disease-modifying therapies, treatment for SMA was primarily supportive care, focusing on managing symptoms like respiratory complications. This has now changed with the introduction of targeted genetic therapies.

How does newborn screening affect SMA prognosis?

Newborn screening for SMA allows for early diagnosis and treatment before symptoms develop. Early intervention with disease-modifying therapies has been shown to produce the best outcomes, significantly improving the prognosis for infants with severe SMA types.

Is SMA curable with modern treatment?

While modern treatments like gene therapy (Zolgensma) can provide a functional copy of the missing gene or increase protein production, they are not a cure. They are designed to halt disease progression and manage symptoms, but they cannot reverse motor neuron loss that has already occurred.

Can adults develop SMA?

Yes, adults can develop SMA. Type 4 SMA, the mildest form, typically has an onset in adulthood, often after age 21. It is characterized by slowly progressing muscle weakness and does not affect life expectancy.

Is it possible for a child with SMA Type 1 to survive into adulthood?

Before the advent of modern treatments, it was extremely rare. However, with the early initiation of new therapies, some children with SMA Type 1 are now surviving past the age of two and reaching motor milestones once thought impossible, fundamentally shifting the prognosis.

What role does the SMN2 gene play in life expectancy?

The SMN2 gene is a backup gene that produces a small amount of functional SMN protein. A person's number of SMN2 copies can significantly influence their lifespan; a higher copy number typically correlates with a milder disease type and a better prognosis.

Do all SMA types affect a person's ability to walk?

No, not all SMA types lead to the inability to walk. Individuals with Type 4 can maintain their mobility throughout their lives, and those with Type 3 can walk, although they may experience a decline in walking ability over time. People with Types 1 and 2, however, are typically unable to stand or walk without assistance.