What is Spinal Muscular Atrophy?
Spinal muscular atrophy (SMA) is a genetic disease that affects the nervous system and muscles. It is caused by a deletion or mutation of the survival motor neuron 1 (SMN1) gene. This gene produces a protein that is essential to the function of the motor neurons, the nerve cells that control muscle movement. Without enough SMN protein, these motor neurons cannot function properly or die, leading to weakness and wasting of the muscles.

Types of SMA
Spinal Muscular Atrophy is classified into four main types (Type 1-4) based on the age of onset and highest physical milestone achieved.
- Type 1 is the most severe type of SMA. Symptoms begin before 6 months of age and patients never sit without support. This is the leading genetic cause of death in infants.
- Type 2 occurs between 6-18 months. Affected individuals never stand or walk without assistance.
- Type 3 begins after 18 months of age. Affected individuals can stand and walk but later lose this ability.
- Type 4 refers to adult-onset forms where patients experience gradually progressive muscle weakness but have near-normal life expectancy.

Causes and Genetics
SMA is inherited in an autosomal recessive pattern, meaning an individual needs two copies of the faulty SMN1 gene, one from each parent, to develop SMA. Everyone has two SMN genes - SMN1 and SMN2. SMN1 encodes for full-length, functional SMN protein whereas SMN2 only produces around 10% of functional protein. In SMA patients, both copies of SMN1 gene are deleted or nonfunctional due to mutations, reducing SMN protein levels. Those with only one SMN1 mutation are carriers and do not experience any symptoms.

Symptoms
The most common early symptoms of SMA include weakness of the arms and legs, poor muscle tone, trouble sitting or standing without support, difficulty swallowing or breathing. Severe SMA patients may even experience paralysis of the muscles of breathing and difficulty feeding. Symptoms vary depending on the type but generally worsen with age.

Diagnosis and Testing
If a child displays early signs of muscle weakness or developmental delays, their doctors may perform several tests to check for SMA. This includes genetic testing to look for mutations in both copies of SMN1 gene, nerve conduction studies to check how well the nerves are working, muscle biopsies and electromyography (EMG). A definitive diagnosis can be made by genetic testing of blood or saliva sample. Prenatal testing is also available for high-risk pregnancies.

Treatment and Management
While there is currently no cure for SMA, various treatment options aim to improve motor function and quality of life. These include posture and breathing exercises, physical therapy for muscle strength, medications and nutritional support. Several promising new gene therapies and medications are under clinical trials that may help increase SMN protein levels and improve motor skills. Early diagnosis through newborn screening and immediate treatment can help manage SMA better. Ongoing research continues for developing a permanent cure.

SMA is a debilitating genetic disorder that causes muscle weakening and atrophy. However, with advancing research, better identification through screening and improved supportive care, patients are living longer with a better quality of life. Significant progress has been made in developing targeted treatments that could potentially halt or reverse the course of this disease. Continued funding and clinical trials are vital to find a cure for SMA in the near future.

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