# Spinal muscular atrophy (SMA)
What is it
Spinal muscular atrophy, abbreviated as SMA, is an inherited disease in which nerve cells in the spinal cord gradually die. These nerve cells, called motor neurons, are responsible for controlling muscle movements. When they are lost, muscles gradually weaken and it becomes increasingly difficult to move.
SMA is caused by a defect in a gene that produces the protein SMN (survival of motor neuron). This protein is essential for the healthy functioning of motor neurons. Without enough of this protein, these cells cannot function properly and eventually die.
The disease occurs in different forms, depending on the age at which symptoms begin and how quickly they progress. Some forms begin in infancy and are severe; others appear only later in life and progress more slowly.
Causes
SMA is a genetic disease that is hereditary. It is caused by a defect in the SMN1 gene, which is located on chromosome 5. If both parents are carriers of the same gene mutation, each child has a 25% chance of developing SMA.
The body normally produces two SMN genes: SMN1 and SMN2. In SMA, the SMN1 gene is missing or damaged. The SMN2 gene can sometimes partially take over its function, but usually not completely. The more functional SMN2 genes a person has, the milder the disease usually progresses.
Research suggests that other factors, such as certain environmental influences and epigenetic changes, can also play a role in how severely the disease manifests. This helps explain why the same gene mutation can sometimes progress differently in different people.
How the disease progresses
SMA is progressive, meaning it generally becomes worse over time. The speed and severity of deterioration depend on the type of SMA.
**Type 1 (infantile SMA, onset before 6 months)**: This is the most severe form. Symptoms appear very early. Without treatment, the disease worsens rapidly. Children may have difficulty breathing due to weakness of the respiratory muscles.
**Type 2 (intermediate, onset 6 to 18 months)**: Symptoms develop somewhat later. The disease worsens more slowly than type 1, but children usually need significant support.
**Type 3 (juvenile, onset after 18 months to adulthood)**: This is milder. Symptoms begin later and progression is slower. Many people can continue walking into adulthood, although with some difficulty.
**Type 4 (adult)**: This is rare and begins only in adulthood. Progression is usually slow.
Modern treatments have been able to significantly change the course of the disease in recent years. When treatment is started early, further deterioration can be delayed or even stopped.
Symptoms by phase
**Early phase**:
- Weakness in the legs, often first noticed as difficulty rolling, sitting or standing
- In infants, sometimes feeding or breathing problems
- Less active and alert than age-matched peers
- Difficulty lifting the head or neck
- Tremor (fine trembling) in the hands
**Further progression**:
- Gradual loss of strength in arms and legs
- Increasing need for assistance with daily activities
- In some, speech problems or difficulty chewing and swallowing
- Possible decrease in muscle mass
- Fatigue increases
- Cough may become weaker
**Advanced phase** (when untreated):
- Severe muscle weakness, sometimes total immobility of limbs
- Dependence on assistance with all movements
- Breathing and coughing problems increase
- Feeding tube may be needed
- In some cases, breathing assistance is required
In children treated early, progression may differ significantly from this picture.
What it means for daily life
The impact of SMA on daily life depends heavily on the type and how quickly the disease progresses, and also greatly on available treatment.
**Mobility**: In milder forms, people can often still cycle, walk or move around, although this becomes tiring. In more severe forms, help is needed to move around, and adapted aids such as wheelchairs or lifts may be necessary.
**Independence**: Depending on the severity, everything from self-care to leisure activities can become more difficult. This sometimes requires help from loved ones or professional care.
**School and work**: Children and young adults can attend education, although it sometimes requires adjustments, such as adapted physical exertion or aids. Working people sometimes have to adapt their workplace.
**Family**: SMA affects the entire family. Parents or partners provide a lot of care, which can be physically and emotionally taxing.
**Lung function**: In severe forms, breathing and coughing function can weaken, which requires precaution, especially with infections.
**Nutrition**: Weakness of muscles for chewing and swallowing can make nutrition more complex; sometimes nutrition is given via a feeding tube.
Many of these challenges can be limited by appropriate treatment, support and adjustments at home and at work or school.
Outlook
The prospects for SMA have improved considerably in recent years thanks to new treatments. These can slow or even stop the progression of the disease, especially when started early.
For **type 1** without treatment, survival was previously limited to a few years. With current treatments, children can survive much longer and sometimes even achieve new skills, although the disease can remain serious.
For **type 2 and 3**, the prospects are better. With treatment, many children can limit or improve their current loss of function; some can even regain certain movements that seemed lost.
For **type 4** (adult-onset), the disease usually progresses slowly, and many people can live a relatively independent life for decades.
Note: these general figures say nothing about the personal course in one person. Much depends on how quickly someone is diagnosed, what treatment is available, and how well they respond to it.
Frequently asked questions
**Is SMA hereditary and can I pass it on to my children?**
SMA is hereditary, but only if both parents are carriers of the same gene mutation. Carriers have no symptoms themselves. If both parents are carriers, there is a 25% chance that each child will develop SMA. Genetic counselling can help provide insight into the risks in your family and your choices.
**Can SMA be prevented?**
Genetic treatments can in some cases correct or compensate for gene abnormalities. This falls under gene therapy and is available in certain situations. However, this is always something that is discussed in consultation with specialists.
**How quickly does someone get worse?**
This varies enormously. In type 1, deterioration can be a matter of weeks to months; in type 3, years. Modern treatment can slow this pattern considerably. Only your own doctor can assess your situation.
**Can SMA be cured?**
Complete cure is not currently possible, but available treatments can very effectively slow or stop the disease. Research continues into new therapies. This is a rapidly changing field.
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_This information never replaces a doctor's judgment. Always discuss your situation with your own healthcare provider._