What is Spinal Muscular Atrophy?

Jake Newby

| 4 min read

A Spinal Muscular Atrophy (SMA) diagnosis can leave families feeling lost and uncertain. SMA is a severe, inherited, progressive neuromuscular disease that causes devastating muscle atrophy and disease-related complications in approximately 4 to 10 per 100,000 live births. The muscles relied on every day to breathe, eat and walk deteriorate, due to the loss of nerve cells in the spinal cord known as motor neurons.

Who does SMA affect?

A person with SMA inherits two copies of a mutated survival motor neuron 1 (SMN1) gene – one coming from the father, and the other from the mother. An adult can unknowingly have one single copy of the defective gene that causes SMA.
SMA can be diagnosed in children of any age. The earlier in life a person is diagnosed with SMA, the more severe the symptoms are likely to be, according to the Centers for Disease Control and Prevention (CDC). SMA can affect a baby’s ability to swallow, breathe, sit, and walk. Without early treatment, SMA can also result in premature death. While SMA in infancy and early childhood is associated with worse outcomes, individuals who develop symptoms later in childhood or in adolescence typically have a more positive prognosis.

What are the types of SMA?

There are five types of SMA but Type 0 is extremely rare. Type 0 symptoms begin prior to birth and historically, result in a low survival rate for infants. The four primary types of SMA are:
Type 1 (severe): About 60% of people with SMA have Type 1, which is also known as Werdnig-Hoffman disease. Symptoms appear at birth or within an infant’s first six months of life. Infants with type 1 SMA have difficulty swallowing and sucking. They are usually unable to hold up their heads or sit, and often need breathing assistance and a feeding tube. If untreated, Type 1 can be fatal early in a baby’s life.
Type 2 (intermediate): Symptoms of type 2 SMA usually appear when a child is between six months and 18 months old. Individuals with SMA Type 2 can typically sit up without help, though they may need help getting into a seated position. This type can take its toll on a person’s lower body, usually leading to an inability to walk or the requirement of a wheelchair.
Type 3 (mild): Also called Kugelbert-Welander or juvenile SMA, Type 3 symptoms usually appear after a child’s first 18 months of life. Some people with Type 3 don’t have signs of disease until early adulthood. Individuals with SMA Type 3 are initially able to walk and have increasingly limited mobility as they age. They may eventually need a wheelchair.
Type 4 (adult): The rare adult form of SMA can appear in late teens and early adulthood, but normally affects people in their mid-30s. It can lead to mild motor impairment. Muscle weakness symptoms progress slowly, so most people with Type 4 live full lives without a loss of mobility.

Newborn screening for SMA

Screening newborns is crucial for early SMA detection. In routine newborn screening, state public health laboratories use dried blood spots collected from a baby’s heel within the first 24-48 hours of their birth to detect the disease. According to CureSMA.org, within three years of SMA being added to the federally recommended list of diseases to screen for at birth, Cure SMA and its advocates ensured that 99% of babies born in the United States are now screened for SMA at birth.

What is the best treatment for SMA?

Currently, there is no cure for SMA. Treatment usually revolves around managing symptoms and preventing complications. But thanks to advances in medicine and technology, individuals with all types of SMA are living longer, active, independent lives.
Many people with SMA benefit from physical and occupational therapy and assistive devices, like crutches, orthopedic braces, walkers and wheelchairs. In some cases, disease-modifying therapy may be recommended by a primary care physician. Gene replacement therapy is another option sometimes recommended for children under the age of 2.
Since the disease is so rare, no two people with SMA have identical experiences. Decisions about care and treatment must be made based on an individual’s unique condition. Always be sure to work closely with a primary care provider (PCP) to make the best health care choices for your specific needs.
Photo credit: Getty Images
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