Is Spinal Muscular Atrophy a Disability?

Spinal muscular atrophy (SMA) is a debilitating disease that can be classified as a disability if symptoms are severe enough to cause impairments. SMA is hereditary and progressive, affecting the central and peripheral nervous systems and voluntary muscle function.

The disease destroys motor neurons in the brainstem and spinal cord.

• Motor neurons are nerve cells responsible for skeletal muscle function, including muscles in the arms, legs, chest, face, throat, and tongue.
• Destruction of motor neurons disrupts signals to the muscles, gradually weakening and wasting them (atrophy).

What is the life expectancy of someone with spinal muscular atrophy?

Life expectancy depends on the severity of the disease:

• Type 0: Babies with SMA type 0 rarely survive beyond 6 months due to fragile respiratory muscles and congenital heart defects.
• Type 1: Most children with SMA type 1 do not survive beyond the age of 2 due to respiratory issues. New treatments have helped prolong their lives and improve mobility.
• Type 2: Most children with SMA type 2 survive into adolescence or young adulthood with current treatments that improve muscle function and quality of life.
• Type 3: With appropriate care and treatment, most patients with SMA type 3 have an average life span. Treatment can improve motor function and slow down the disease.
• Type 4: People with SMA type 4 have a normal life expectancy and remain mobile and active with treatment that prevents complications and slows disease progression.

Who is affected by the disease?

The earlier the disease develops, the more severe it is:

• About 60% of children with SMA are born with the condition or develop it within the first 6 months of life. Children who develop SMA after 6 months may be able to sit but most cannot walk.
• Teens who develop the disease may initially have muscle weakness, but some eventually lose the ability to stand or walk.
• Adult-onset of SMA is rare and usually results in muscle weakness, but most can manage the condition and remain mobile with treatment and exercise.

What are the signs and symptoms of spinal muscular atrophy?

Symptoms vary depending on the type and severity of the disease. Some people are never able to sit, stand, or walk, while others gradually lose these abilities due to muscle loss.

There are five types of spinal muscular atrophy:

Type 0 (SMA0)

Type 0 SMA is the rarest and most severe form, developing in babies in the womb. It causes decreased fetal movement, congenital heart defects, breathing difficulty, facial paralysis, low muscle tone, and muscle weakness.

Type 1 (SMA1)

Also known as Werdnig-Hoffman disease, type 1 is a severe form of SMA that presents at birth or before 6 months old.

• A child with type 1 SMA cannot sit up without support and has trouble breathing, sucking, and swallowing.

Type 2 (SMA2)

Type 2 accounts for about 20% of SMA cases and develops in children between 6-18 months old. It usually affects the legs more than the arms.

• An affected child may be able to sit without support but may not be able to stand or walk and may have respiratory difficulties, abnormal facial features, and small head size.

Type 3 (SMA3)

Also known as juvenile-onset SMA or Kugelberg-Welander disease, type 3 SMA is a milder disease that develops after 18 months old and makes up 30% of all SMA cases.

• Children with type 3 SMA can stand and walk without support but have difficulty with running, climbing stairs, and getting up from a chair. Most develop foot deformities, scoliosis, and respiratory issues and become wheelchair-dependent.

Type 4 (SMA4)

Type 4 SMA is a mild form that develops in adulthood, usually after age 30, and accounts for less than 5% of cases.

• Symptoms may include muscle weakness, twitching, and breathing difficulties. Most people with type 4 SMA can maintain mobility with appropriate treatment and exercise.

What causes spinal muscular atrophy?

SMA is caused by inherited genetic defects, most commonly from mutations in both copies of the SMN1 gene on chromosome 5. The SMN1 gene encodes the SMN protein, which maintains motor neuron health.

In most SMA cases, both copies of the SMN1 gene are missing. Some people have mutations that cause low production of SMN protein. A low level of SMN protein destroys motor neurons, weakening muscles. Extra copies of the SMN2 gene can compensate for defective SMN1 genes and result in milder forms of the disease.

If one copy of the SMN1 gene is mutated, a person may be a carrier without being affected by the disease. If both parents are carriers, a child has about a 25% chance of developing SMA.

Less common forms of SMA are caused by mutations in other genes.

How is spinal muscular atrophy diagnosed?

Diagnosis includes a classification of SMA and tests such as genetic testing, blood tests, electromyogram, nerve conduction study, and muscle biopsy.

Can spinal muscular atrophy be treated?

SMA is not curable, but treatment can alleviate symptoms, slow disease progression, and improve quality of life.

• Treatment effectively manages symptoms in SMA4 patients, allowing them to remain mobile.
• Early diagnosis and treatment can improve outcomes for patients with SMA2 and SMA3.
• New gene therapies and disease-modifying medications targeting the SMN genes have improved prognosis.

Spinal muscular atrophy has been added to newborn screening panels, allowing for early diagnosis and prompt treatment.

What is the treatment for spinal muscular atrophy?

Treatment depends on disease severity and includes disease-modifying medications, symptom and complication therapies, and participation in clinical trials for new therapies.

Disease-modifying therapies

The FDA has approved three medications to treat SMA caused by a missing or mutated SMN1 gene:

• Nusinersen sodium (Spinraza): Administered through spinal injection, it modifies the SMN2 gene to increase production of functional SMN protein.
• Onasemnogene abeparvovec-xioi (Zolgensma): Administered through intravenous infusion, it delivers a fully functional SMN1 gene into motor neurons.
• Risdiplam (Evrysdi): An oral solution that modifies the SMN2 gene to produce more functional SMN protein.

Symptom and complication therapies

Therapies to relieve symptoms and alleviate complications vary depending on the patient’s condition, including breathing support, feeding tubes, physical and occupational therapies, supportive aids, and surgery.

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