Spinal muscular atrophy is a genetic condition that affects how muscles work and move. When someone has SMA, his or her muscles gradually become weaker because the nerve cells that control movement start to break down. This condition impacts people differently depending on the type and when symptoms first appear.
Understanding SMA helps families recognize early signs, know what to expect, and learn about the medical options available today. While SMA is a serious condition, recent advances in treatment have changed what’s possible for people living with this disease.
Let’s explore what spinal muscular atrophy is, how it affects the body, and what families and patients should know about living with SMA.
What Spinal Muscular Atrophy Does to the Body
SMA is a genetic disorder that affects the motor neurons in the spinal cord. These motor neurons are responsible for sending signals from the brain to the muscles, telling them when and how to move.
How SMA Affects Motor Neurons
In a person with SMA, a specific gene called SMN1 is either missing or not working properly. This gene produces a protein that motor neurons need to survive and function. Without enough of this protein, motor neurons gradually die off.
As motor neurons deteriorate, the muscles they control stop receiving signals. This causes the muscles to weaken and eventually waste away, a process called muscle atrophy. The weakness typically affects muscles closest to the center of the body first, like those in the shoulders, hips, and back.
Which Muscles Are Affected Most
SMA primarily impacts voluntary muscles, the ones a person consciously controls for activities like walking, sitting up, and moving his or her arms. Muscles used for breathing and swallowing can also be affected, especially in more severe types of SMA.
The muscles in a person’s arms and legs become weaker over time, making it harder to perform everyday tasks. In infants with severe SMA, even holding up their head or sitting without support becomes impossible.
Interestingly, SMA does not affect a person’s intelligence, sensory abilities, or emotional development. Someone with SMA thinks, feels, and perceives the world just like anyone else.
The Different Types of SMA
Doctors classify SMA into several types based on when symptoms begin and how severe they are. Each type follows a different pattern and affects people in distinct ways.
Type 0 and Type 1 SMA
Type 0 is the rarest and most severe form. Babies with Type 0 SMA show signs even before birth, with reduced movement in the womb. These infants are born with severe muscle weakness and breathing problems, and sadly, most do not survive beyond the first few months of life.
Type 1 SMA, also called Werdnig-Hoffman disease, is the most common severe form. Symptoms appear within the first six months of life. A baby with Type 1 SMA cannot sit up without support, has difficulty swallowing and breathing, and shows a weak cry. Without treatment, most children with Type 1 do not survive past age two, though new therapies are changing this outcome.
Type 2 SMA
Type 2 SMA symptoms typically appear between 6 and 18 months of age. A child with Type 2 can sit without support but cannot stand or walk independently. He or she may achieve developmental milestones like sitting up, but then motor skills plateau or decline over time.
Children with Type 2 SMA often develop scoliosis as their back muscles weaken. They may also experience breathing difficulties, especially during sleep or when lying down. With proper care and support, many people with Type 2 SMA live into adulthood.
Type 3 SMA
Type 3 SMA, or Kugelberg-Welander disease, appears after 18 months of age, sometimes not until childhood or early adolescence. A person with Type 3 SMA learns to walk independently but may lose this ability over time as muscles weaken.
Individuals with Type 3 typically have a normal lifespan. Their symptoms progress more slowly, and many maintain the ability to walk with assistance or use wheelchairs for mobility. Muscle weakness gradually affects daily activities, but most people with Type 3 SMA can live independently with adaptive equipment.
Type 4 SMA
Type 4 is the mildest and rarest form, with symptoms beginning in adulthood, usually after age 30. Someone with Type 4 SMA experiences gradual muscle weakness, often starting in the legs. The progression is very slow, and most people with Type 4 maintain their ability to walk and remain active throughout their lives.
This type often goes undiagnosed for years because the symptoms are mild and develop so gradually. Many people with Type 4 SMA live normal lifespans without significant disability.
Early Warning Signs Parents Should Know
Recognizing SMA early can make a significant difference in treatment outcomes, especially with newer therapies available.
Signs in Infants
A baby with SMA may seem unusually floppy or have poor muscle tone, a condition doctors call hypotonia. When a parent picks up the infant, he or she may feel like a rag doll, with little resistance in the limbs.
Infants with SMA often have difficulty feeding because the muscles needed for sucking and swallowing are weak. They may tire easily during feedings or take a long time to finish a bottle. Some babies also have a weak cry that sounds softer than typical infant cries.
Movement limitations become apparent, too. A baby with SMA may not reach typical milestones like rolling over, sitting up, or bearing weight on his or her legs. The infant might also have breathing difficulties, with shallow breaths or rapid breathing patterns.
Signs in Older Children
In children who develop SMA later, parents might notice their child becoming clumsier or falling more frequently. A child who previously walked well may start tripping often or having trouble climbing stairs.
Muscle weakness in the shoulders and hips becomes noticeable. A child may struggle to lift his or her arms above the head or have difficulty getting up from the floor. Some children develop a waddling gait as their hip muscles weaken.
Hand tremors are another common sign. A child’s hands may shake slightly when he or she tries to hold something or perform fine motor tasks like buttoning clothes or writing.
How SMA Is Diagnosed
Diagnosing SMA involves several steps to confirm the condition and determine its type.
Genetic Testing
The definitive way to diagnose SMA is through genetic testing. A simple blood test can identify whether the SMN1 gene is deleted or mutated. This test is highly accurate and can confirm SMA in most cases.
Genetic testing also helps identify carriers. Someone who carries one faulty copy of the SMN1 gene won’t have SMA but can pass it to his or her children. If both parents are carriers, each pregnancy has a 25% chance of resulting in a child with SMA.
Other Diagnostic Tests
Doctors may perform additional tests to assess the extent of muscle weakness and nerve damage. An electromyography, or EMG, measures the electrical activity in muscles and can show patterns consistent with SMA.
Muscle biopsies, though less common now, can reveal the characteristic muscle wasting seen in SMA. Creatine kinase blood tests check for elevated levels of this enzyme, which can indicate muscle damage.
Newborn Screening
Many places now include SMA in routine newborn screening panels. This allows doctors to identify affected babies before symptoms appear, giving families the opportunity to start treatment early when it may be most effective.
Treatment Options Available Today
While there is no cure for SMA, several treatments can slow progression and improve quality of life.
Gene Therapy
Zolgensma is a one-time gene therapy approved for treating SMA in young children. This treatment delivers a working copy of the SMN1 gene directly into a child’s cells, allowing his or her body to produce the protein motor neurons need.
The treatment works best when given early, ideally before symptoms become severe. Children who receive Zolgensma early may achieve motor milestones and avoid some of the severe complications of SMA.
SMN2-Targeting Medications
Spinraza is an FDA-approved medication that increases production of the SMN protein from the SMN2 gene, a backup gene everyone has. The medication is given through injections into the spinal fluid and must be administered regularly throughout a person’s life.
Evrysdi is a newer oral medication that also boosts SMN protein production. Because it comes in liquid form, it’s easier to administer, especially for young children or people who have difficulty with injections.
Supportive Care and Therapies
Physical therapy helps maintain muscle strength and flexibility for as long as possible. A physical therapist works with the patient to develop exercises suited to his or her abilities and needs.
Occupational therapy focuses on adapting daily activities and using assistive devices to maintain independence. An occupational therapist might recommend special utensils, computer adaptations, or mobility aids.
Respiratory support becomes necessary for many people with SMA. This can range from nighttime breathing assistance to full-time ventilation support, depending on how severely breathing muscles are affected.
Living Day to Day with SMA
People with SMA and their families develop routines and adaptations that help manage the condition.
Mobility and Movement
Many individuals with SMA use wheelchairs for mobility. Modern power wheelchairs allow someone to move independently even when his or her muscles are very weak. Adaptive controls can be customized based on which muscles the person can still use effectively.
For people with milder SMA, walkers or braces may provide enough support to maintain some walking ability. Standing frames help children and adults maintain bone strength and circulation even when they cannot walk.
Breathing and Respiratory Care
Respiratory infections pose serious risks for people with SMA because weak breathing muscles make it hard to cough effectively. Regular monitoring of lung function helps catch problems early.
Some individuals need breathing support, especially during sleep. BiPAP machines assist with breathing overnight, giving respiratory muscles a rest. In more severe cases, a person may need a ventilator for full-time breathing support.
Cough assist devices help clear mucus from the lungs when natural coughing is too weak. This reduces the risk of pneumonia and other respiratory complications.
Nutrition and Feeding
Swallowing difficulties can make eating challenging for people with SMA. Some may need feeding tubes to ensure they get adequate nutrition and stay hydrated. A gastrostomy tube, or G-tube, can be placed in the stomach for direct feeding.
Working with a nutritionist helps ensure the person gets proper calories and nutrients to maintain health and energy. Weight management is important too, as being overweight puts extra strain on weak muscles.
