Overview Of Spinal Muscular Atrophy (SMA)
Spinal Muscular Atrophy (SMA) is a group of disorders of the motor neurons (motor cells). These disorders are passed down through families (inherited) and can appear at any stage of life. The disorder leads to muscle weakness and atrophy.
Commonly Associated With
Werdnig-Hoffmann disease; Kugelberg-Welander disease
Causes Of Spinal Muscular Atrophy (SMA)
SMA is a collection of different motor nerve diseases. Grouped together, it is the second leading cause of hereditary neuromuscular disease, after Duchenne muscular dystrophy.
Most of the time, a person must get the defective gene from both parents to be affected. The most severe form is SMA type I, also called Werdnig-Hoffman disease. Infants with SMA type II have less severe symptoms during early infancy, but they become weaker with time. SMA type III is a less severe form of the disease.
In rare cases, SMA begins in adulthood. This is the mildest form of the disease.
A family history of SMA in an immediate family member (such as brother or sister) is a risk factor for all types of the disorder.
Symptoms Of Spinal Muscular Atrophy (SMA)
Symptoms of SMA are:
- Infants with SMA type I are born with very little muscle tone, weak muscles, and feeding and breathing problems.
- With SMA type II, symptoms may not appear until age 6 months to 2 years.
- Type III SMA is a milder disease that starts in childhood or adolescence and slowly gets worse.
- Type IV is even milder, with weakness starting in adulthood.
- Often, weakness is first felt in the shoulder and leg muscles. Weakness gets worse over time and eventually becomes severe.
Symptoms of spinal muscular atrophy (SMA) in an infant:
- Breathing difficulty with shortness of breath and labored breathing, leading to a lack of oxygen
- Feeding difficulty (food may go into the windpipe instead of the stomach)
- Floppy infant (poor muscle tone)
- Lack of head control
- Little movement
- Weakness that gets worse
Symptoms in a child:
- Frequent, increasingly severe respiratory infections
- Nasal speech
- Posture that gets worse
- With SMA, the nerves that control feeling (sensory nerves) are not affected. So, a person with the disease can feel things normally.
Exams & Tests
The health care provider will take a careful history and perform a brain/nervous system (neurologic) examination to find out if there is:
- A family history of neuromuscular disease
- Floppy (flaccid) muscles
- No deep tendon reflexes
- Twitches of the tongue muscle
Tests for spinal muscular atrophy (SMA) that may be ordered include:
- Aldolaseblood test
- Erythrocyte sedimentation rate (ESR)
- Creatine phosphate kinase blood test
- DNA testing to confirm the diagnosis
- Electromyography (EMG)
- Lactate/pyruvate
- MRI of the brain, spine, and spinal cord
- Muscle biopsy
- Nerve conduction study
- Amino acid blood tests
- Thyroid-stimulating hormone (TSH) blood test
Treatment Of Spinal Muscular Atrophy (SMA)
There is no treatment to cure the weakness caused by the disease. Supportive care is important. Breathing complications are common in the more severe forms of SMA. To help with breathing, a device or machine called a ventilator may be needed.
People with SMA also need to be watched for choking. This is because the muscles that control swallowing are weak.
Physical therapy is important to prevent contractions of muscles and tendons and abnormal curvature of the spine (scoliosis). Bracing may be needed. Surgery may be needed to correct skeletal deformities, such as scoliosis.
Two recently approved treatments for SMA areonasemnogene abeparvovec-xioi (Zolgensma) and nusinersen (Spinraza). These medicines are used to treat certain forms of SMA. Talk with your health care provider to see if either of these medicines is right for you or your child.
