Understanding Spinal Muscular Atrophy
Naufan Cmi
What is Spinal Muscular Atrophy?
Spinal muscular atrophy (SMA) is a genetic disease that affects the part of the nervous system called the anterior horn cell, located in the spinal cord. It results in loss of motor neurons and causes progressive muscle wasting and weakness. SMA is caused by a deficiency in the SMN1 gene responsible for producing survival motor neuron (SMN) protein. The loss or malfunctioning of motor neurons caused by deficient SMN protein leads to muscle weakness and atrophy.
Types and Causes of SMA
There are four main types of Spinal Muscular Atrophy categorized based on the age of onset and highest physical milestone achieved.
Type 1 SMA (Werdnig-Hoffmann disease) is the most severe form. Symptoms begin before 6 months of age and the patient is never able to sit without support.
Type 2 SMA (intermediate form) symptoms start between 6-18 months. The patient can sit but cannot stand or walk.
Type 3 SMA (Kugelberg-Welander disease or juvenile form) symptoms appear after 18 months of age. The child is able to stand and walk but may lose this ability over time.
Type 4 SMA (adult form) symptoms start in late teenage years or adulthood. It progresses more slowly than the other forms.
All types of SMA are autosomal recessive disorders caused by mutations in the survival motor neuron 1 (SMN1) gene located on chromosome 5. While humans have two SMN genes, only SMN1 produces sufficient amounts of survival motor neuron (SMN) protein required for motor neuron function. Mutations in both copies of the SMN1 gene decreases or eliminates SMN protein production.
Symptoms of Spinal Muscular Atrophy
The signs and symptoms of SMA vary depending on the type but can include:
- Muscle weakness - The muscles involved in breathing and swallowing are often the first to be affected.
- Muscle wasting (atrophy) - The muscles become smaller and less defined over time.
- Joint and skeletal abnormalities - Scoliosis or an unusually curved spine is common. Hips can also protrude outward.
- Difficulty breathing or respiratory infections - Breathing muscles become too weak to clear secretions from the lungs.
- Difficulty eating - Chewing and swallowing issues arise from facial and mouth muscle impairment.
- Fatigue - Physical activity becomes very tiring due to muscle deterioration.
- Delays in developmental milestones - Sitting up, crawling, standing and walking may never be achieved or lost over time.
Diagnosis of Spinal Muscular Atrophy
SMA is diagnosed through a clinical exam and genetic testing. If symptoms suggest SMA, DNA testing is performed to check for mutations in the SMN1 gene. A nerve conduction study called electromyography (EMG) may also be done to evaluate muscle and nerve functioning. Since symptoms are similar to other motor neuron diseases, diagnostic confirmation through genetic testing is important. Prenatal testing during pregnancy can also detect SMA in an unborn baby. Carrier testing is available for adults who may be carriers to assess inheritance risk in family planning.
Treatment and Management of SMA
There is currently no cure for SMA. Treatment focuses on care and support to maximize quality of life and function. Physiotherapy can maintain mobility and muscle tone. Braces, walkers and wheelchairs may be used for mobility assistance. Occupational therapy helps with activities of daily living and specialized equipment. Pulmonary care includes clearance techniques and ventilation support if needed. Nutrition support through feeding tubes is common in more severe cases with swallowing and breathing problems. Several new treatment approaches are currently being studied including gene therapy, neuroprotective drugs and stem cell transplants. The first SMA gene replacement drug was approved in late 2020 and offers great hope as a disease-modifying treatment. Proper management through a multidisciplinary team approach is important for managing SMA outcomes and extending lifespan.
Prevention and Screening of Spinal Muscular Atrophy
Carrier screening and prenatal diagnosis are available to help reduce risk and guide family planning decisions. Women can be screened prior to pregnancy to determine carrier status. If both parents are carriers, each pregnancy has a 1 in 4 chance of a child being affected with SMA. Prenatal diagnostic testing by chorionic villus sampling (CVS) or amniocentesis can determine if a fetus is affected. Newborn screening for SMA is also recommended and is incorporated into state newborn screening panels in several parts of the world to facilitate early treatment initiation. Early identification is crucial since emerging therapies are most effective before symptom onset. Genetic counseling helps evaluate inheritance risk and review available testing and reproductive options for families with a history of SMA.
Prognosis of Spinal Muscular Atrophy
Prognosis depends on several factors including the type of SMA, severity of symptoms, age of onset and access to treatment. Type 1 SMA is usually fatal in early childhood without respiratory support. Type 2 has the second poorest outcome with many individuals not living past young adulthood. Type 3 has a more variable prognosis and some adults may have a normal lifespan. Individuals with Type 4 have the most favorable long term prognosis. The recent availability of new gene-based therapies provides hope for significantly improved outcomes in SMA, even for infants with severe Type 1 disease. Lifespan and quality of life can now be substantially prolonged with ongoing care and newer treatment options. Early diagnosis and prompt intervention also supports better SMA management and outcomes.
About Author
Alice Mutum, is a seasoned senior content editor at Coherent Market Insights, leveraging extensive expertise gained from her previous role as a content writer. With seven years in content development, Alice masterfully employs SEO best practices and cutting-edge digital marketing strategies to craft high-ranking, impactful content. As an editor, she meticulously ensures flawless grammar and punctuation, precise data accuracy, and perfect alignment with audience needs in every research report. Alice's dedication to excellence and her strategic approach to content make her an invaluable asset in the world of market insights.
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