Spinal Muscular Atrophy

Gillette Children’s Specialty Healthcare offers one of the region’s top neuromuscular programs for managing incurable but treatable conditions, such as spinal muscular atrophy. In fact, Gillette has one of the largest groups of pediatric neurologists and neurosurgeons in the Twin Cities area. Our Center for Pediatric Neurosciences is the only one in the region integrating research and clinical services.

The Muscular Dystrophy Association recognizes Gillette’s Neuromuscular Clinic as a partner in providing interdisciplinary care for people who have spinal muscular atrophy (SMA).

Why Choose Gillette?


SMA is a condition affecting the motor nerves that control muscular function—impeding activities such as crawling, walking, breathing and eating. Because the nerves SMA affects lack sufficient amounts of a protein that maintains function, those nerves can’t carry signals from the brain to the muscles. That in turn causes muscle weakness and decreased muscle mass (atrophy).

Types of Spinal Muscular Atrophy

The type of SMA (I, II, or III) is determined by the age of onset and the severity of symptoms.

  • SMA I, also called infantile onset or Werdnig-Hoffmann disease, is the most severe form of the condition. Symptoms of SMA I typically develop before or when infants reach 6 months of age. Most infants diagnosed with SMA I show severe muscle weakness and floppiness (hypotonia). They have difficulty gaining strength and can’t sit independently. The muscle weakness also causes difficulty with swallowing and breathing.
  • SMA II, sometimes called intermediate SMA, causes muscle weakness and hypotonia, but the problems are less severe than with SMA I. Babies and toddlers with SMA II learn to sit on their own, but have difficulty standing or walking. As they grow, some children lose the ability to stand and move freely. They then need to use mobility devices, such as powered wheelchairs.
  • SMA III, also known as late-onset SMA or Kugelberg-Welander disease, develops in children who are 18 months or older. Children who have SMA III walk independently, but might have trouble jumping or using stairs. The severity of this form varies widely. Some people aren’t diagnosed until well into adulthood. In those cases, the condition is sometimes called SMA IV or adult-onset SMA.

Spinal Muscular Atrophy Symptoms

The symptoms of SMA differ depending on type. The most severe form of SMA typically affects essential functions that are important during an infant’s first 6 months of life. Less severe forms of SMA often have milder symptoms that don’t develop until later in life. Even in milder cases, the disease is progressive—but to a lesser extent.

Symptoms in infants:

  • Gross motor delay or loss of skills
  • Difficulty breathing
  • Difficulty feeding
  • Limp or floppy muscles (poor muscle tone or hypotonia)
  • Poor head control
  • Lack of movement
  • Muscle weakness that grows worse
  • Failure to thrive

Symptoms in children:

  • Delay in gross motor skills, like walking, or the loss of skills already mastered
  • Frequent respiratory infections that worsen with each occurrence
  • A nasal sound to speech
  • Worsening posture
  • Progressive scoliosis

Spinal Muscular Atrophy Causes, Incidence and Risk Factors

SMA is caused by a mutation (change) in the survival motor neuron 1 gene (SMN1 gene). The SMN1 gene encodes a protein (called the survival motor neuron protein), which helps motor neurons grow and function properly. Motor neurons are the conducting cells of the nervous system; they control muscle movement. When a gene mutation decreases the amount of protein, the patient progressively loses motor neurons. In other words, the ability to control muscle movement gets progressively worse.

The most common SMN1 change is a deletion, which means a piece of the gene is missing. Most people who have SMA have two deletions—one in each copy of the SMN1 gene. A small percentage of people who have SMA (roughly 5 percent) have one deleted copy and a different change in the second copy of the SMN1 gene.

SMA is a hereditary condition that affects both males and females. People who have SMA have a mutation in both copies of the SMN1 gene.

Parents of children who have SMA are usually carriers, meaning one copy of their SMN1 gene has a mutation and the other copy is normal.  If both parents are carriers, there is a 1 in 4 chance that a child will have SMA. Carriers don’t show symptoms of SMA and usually have no history of the condition in their family.

In most cases, both parents of a child who has SMA are carriers. In a small amount of cases, SMA develops from a new mutation in either the formation of the egg or the sperm.  The chance that someone in the general population is an SMA carrier is approximately 1 in 50.

Spinal Muscular Atrophy Tests

Tests and examinations used to diagnose SMA might include:

  • A Physical Examination: This assesses gross motor abilities.
  • Electromyography Testing (EMG): An EMG involves inserting a very thin needle (electrode) into the muscle. The electrode emits a mild electrical current through the nerves to measure the muscle’s ability to respond to stimulation.
  • Genetic Testing: This blood test identifies mutations in the SMN1 gene responsible for SMA.
  • Muscle Biopsy Test: Doctors remove a small sample of tissue and examine it under a microscope, looking for signs of muscle degeneration.

Spinal Muscular Atrophy Treatment and Services

Although there is no cure, supportive care can minimize the complications SMA causes. Current research aims at slowing, and eventually preventing, the muscle degeneration associated with the disease. 

Once we establish a diagnosis, our team works with patients and their families to create customized treatment plans that address their needs. Because SMA isn’t curable, regular checkups are important to minimize the progression of symptoms and avoid secondary complications.

As our SMA patients reach adulthood, we continue to provide age-appropriate care through Gillette Lifetime Specialty Healthcare for teens (16 and older) and adults.

Patients who have SMA often see experts in these specialties and services:

Medical and Specialties

Testing and Diagnostic Services

Rehabilitation Therapies

Family Support

For more information about the comprehensive services we provide at Gillette, search Conditions and Care.

Publications and Resources

Meet Jessica

Find out how we're moving Jessica forward.

Read Her Story »

Meet Chloe

We're matching kids like Chloe with the technology they need to be independent.

Read Her Story »