Hope on the Horizon for Spinal Muscular Atrophy (SMA)
Saunder M. Bernes, MD
August is Spinal Muscular Atrophy (SMA) Awareness Month. It’s also the first official observance of the disease since a major treatment milestone was reached back on December 23, 2016 when the FDA announced it had approved the first-ever approved therapy for SMA called Spinraza. Phoenix Children’s is a select hospital in Arizona to administer it, and we’re definitely in good company across the nation.
First, a quick background on spinal muscular atrophy: it is an autosomal recessive (meaning both males and females are equally affected) genetic disease that affects the motor neurons in the spinal cord.
More specifically, SMA is the result of a mutation in the survival motor neuron gene (SMN1). In a healthy child, this gene produces a protein called survival motor neuron protein which is critical to the function of nerves that control a child’s muscles. Without that protein, those nerve cells function improperly and eventually die. The outward effect on a child is progressive debilitation and often fatal muscle weakness.
For SMA to occur, loss of copies of the gene, one inherited from each parent, are necessary. When both parents are carriers, there is a 1 in 4, or 25%, chance, with each pregnancy, to have a child with SMA. Carrier testing for the general population is technically difficult and usually available only if a previously affected child in the family has been studied.
How Does Spinraza Work?
Did you ever have a puzzle that was missing a piece or two? Let me explain. Most patients with SMA have at least one copy of survival motor neuron gene 2 (SMN2) also known as the SMA “backup gene.” Due to a splicing error, most SMN protein created by SMN2 is missing an important piece called exon 7 not unlike a puzzle missing a piece. That’s where the new therapy comes in. Spinraza is an antisense drug that are essentially small snippets of synthetic genetic material that bind to ribonucleic acid so they can be used to fix those splicing errors in genes like SMN2. Spinraza actually targets SMN2 and creates a more complete SMN protein (completing the puzzle) and limits the muscle weakness and debilitation/loss of function.
In the U.S., spinal muscular atrophy (SMA) occurs in 1 in 6,000 births a year. In Arizona, there will be 10 -15 children who have SMA every year. Early diagnosis and treatment can make all the difference in outcomes. But that’s just the problem - spinal muscular atrophy can be difficult to diagnose, as symptoms can look like other conditions or medical problems. And to make matters worse, each child may experience symptoms differently. Always consult your child's doctor for a diagnosis.
There are 4 types of spinal muscular atrophy based on symptoms and age of onset:
- Type I (also called Werdnig-Hoffman or infantile-onset SMA). This is the most severe type of SMA and may be present at birth. Infants have problems holding their head, sucking, feeding, swallowing, and typically move very little. The muscles of the chest are also affected. The motion of the tongue is described as having "worm-like" movements. Death results usually by the age of two to six years from breathing problems.
- Type II (juvenile SMA, intermediate SMA, or chronic SMA). This form of SMA is seen in children from six months to 18 months of age. They typically have generalized muscle weakness and may require braces, walkers, or a wheelchair for assistance. Life-expectancy often extends into adulthood.
- Type III [also called (Wohlfart-) Kugelberg-Welander or mild SMA]. This form of SMA affects children older than 18 months of age or as late as adolescence. These children show signs of clumsiness, difficulty walking, mild muscle weakness, and may have delayed motor development. These children live long into their adult years.
- Type IV. This form of SMA affects adults in their 30s and 40s, resulting in a walking disability.
Methods of Diagnosing SMA
The diagnosis of spinal muscular atrophy is made after the sudden or gradual onset of specific symptoms and after diagnostic testing. During the physical exam, your child's doctor will obtain a complete medical history of your child, and may also ask if there is a family history of any medical problems.
Currently, if the diagnosis of SMA is suspected, genetic testing is usually the first test. Diagnostic tests that may be done to confirm the diagnosis of spinal muscular atrophy include:
- Blood tests - These include genetic tests and measurements of a muscle enzyme (CK).
- Muscle biopsy - A small sample of the muscle is removed and examined to determine and confirm a diagnosis or condition.
- Genetic tests - Diagnostic tests that evaluate for conditions that have a tendency to run in families.
- Electromyogram (EMG) - A test that measures the electrical activity of a muscle or a group of muscles. An EMG can detect abnormal electrical muscle activity due to diseases and neuromuscular conditions.
Treatment of spinal muscular atrophy
While we are very excited about Spinraza, your child’s health care provider will figure out the best treatment based on:
- The age of your child
- His or her overall health and medical history
- Severity of your child’s sickness
- How well your child can handle specific medications, procedures, or therapies
- How long the condition is expected to last
- Your opinion or preference
It is not known if presymptomatic treatment is curative. The key to medically managing spinal muscular atrophy is through early detection.
The goal of treatment is to prevent respiratory problems and provide adequate nutritional care to the child since the swallowing and breathing muscles can be affected by this condition.
The extent of the problem is dependent on the severity of the condition and the presence of other problems that could affect the child. In severe cases, a breathing machine may be required to help the child breathe easier.
The health care team educates the family after hospitalization on how to best care for their child at home and outlines specific clinical problems that require immediate medical attention by his or her doctor. A child with spinal muscular atrophy requires frequent medical evaluations throughout his or her lifespan.
The key to battling SMA is twofold:
- Pediatricians need to be aware of SMA signs and symptoms but then to consider SMA as a possible diagnosis
- Early diagnosis is key to the success of treatment and outcome
If you’d like more information about treatment of spinal muscular atrophy at Phoenix Children’s, contact Nancy Quay, MS, RN at 602-933-0446 or firstname.lastname@example.org.