Spinal Muscular Atrophy

Spinal Muscular Atrophy

Nancy Bass, MD and Robbie
Nancy Bass, MD and Robbie

In December 2016, the FDA approved the first and only prescription drug for the treatment of adults and children with spinal muscular atrophy, a rare and often fatal genetic disease. The new medication, Spinraza (nusinersen), is injected directly into the fluid surrounding the spinal cord and has shown great promise when used to treat infants. Improvements in motor milestones such as head control, sitting, rolling, crawling, standing and walking have been reported.

At UH Rainbow Babies & Children’s Hospital, our dedicated specialists embrace new treatment options like this, as they strive to provide a comprehensive, team approach to the treatment and care of SMA patients of all ages. Historically, SMA has been considered virtually untreatable with medical management used primarily to ensure adequate nutrition and avoid or delay respiratory failure. With the recent approval of Spinraza, we are pleased to offer SMA patients and their families new hope.

What is SMA?

Spinal muscular atrophy (SMA) is a neurological disease caused by a defect in a specific gene called the survival motor neuron (SMN). The SMN gene is recessive which means that both parents must carry the abnormal gene for their children to be at risk. When this is true, one in four pregnancies will result in SMA.

This disease is considered the number one genetic cause of death for infants but, thankfully, is quite rare, affecting approximately 1 in 10,000 babies. One in every fifty adults may be a carrier of the recessive gene. In patients with SMA, the survival motor neuron is either missing some information or contains an extra copy of the gene. As a result, the SMNs do not produce a protein that is required for the proper function of the nerves in the spinal cord which control muscle movement. Without this protein, the muscles don’t receive the messages they need to move properly so they become wasted and progressively weaker. This can include those muscles necessary for breathing and swallowing so the condition has the potential to be life threatening.

Some patients may never sit or walk unaided, or, if they do learn, may lose these skills as the disease progresses. Cognitive function is not affected by the disease.

SMA may become symptomatic at different stages of life and is categorized as four types.

Type I

Signs of SMA present in the first three to four months of life and may include sucking/swallowing problems and limited overall movement. This is the most severe form of the disease with a typical life span of 2-6 years. Death is most often due to respiratory failure.

Type II

Also called juvenile SMA, symptoms appear in children at 6-18 months of age. Characterized by generalized muscle weakness, children may require braces, walkers or wheelchair assistance. Many live into adulthood.

Type III

A milder type of SMA, the symptoms appear between 18 months of age and adolescence. Symptoms include clumsiness, difficulty walking and mild muscle weakness. Patients typically live well into adulthood.

Type IV

This type of SMA affects adults in the 30s and 40s and results in a mild to moderate walking disability.

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