What is the definition of spinal muscular atrophy?
SMA is a hereditary disorder that affects the central nervous system, peripheral nervous system, and voluntary muscle movement (skeletal muscle).
The majority of nerve cells that regulate muscles are found in the spinal cord, which explains why the disease’s name includes the word spinal. The primary effect of SMA is on muscles, which do not receive impulses from these nerve cells. When muscles aren’t stimulated by nerve cells, they atrophy, which is a medical term for shrinking.
SMA is a motor neuron disease that causes the loss of nerve cells called motor neurons in the spinal cord.
The most common form of SMA (chromosome 5 SMA, also known as SMN-related SMA) has a wide range of onset, symptoms, and progression rates. Types 1 through 4 of chromosome 5-related SMA, which is commonly autosomal recessive, are categorised to account for these variances.
The age at which SMA symptoms first appear closely coincides with the severity of motor function impairment: the younger the onset, the greater the impact on motor function. Children who show symptoms at birth or early in childhood usually have the lowest degree of functioning (type 1). SMA that develops later in life and has a milder course (types 2 and 3, and type 4 in teenagers or adults) is associated with higher levels of motor function.
What is the cause of SMA?
SMA is caused by a lack of the motor neuron protein SMN, which stands for “survival of motor neuron.” This protein appears to be required for appropriate motor neuron function, as its name suggests. In motor neurons, SMN plays a critical function in gene expression. Its shortage is caused by genetic faults (mutations) in a gene named SMN1 on chromosome 5. A deletion of a full region of the SMN1 gene, called exon 7, is the most prevalent mutation in people with SMA.
Because there is 99 percent similarity between these two genes, neighboring SMN2 genes can partially compensate for nonfunctional SMN1 genes.
Mutations in genes other than SMN1 cause other rare forms of SMA (non-chromosome 5).
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What are some of the signs and symptoms of SMA?
The symptoms of SMA are varied, ranging from mild to severe.
SMA generally affects the muscles closest to the center of the body (proximal muscles) more than the muscles further away (distal muscles).
SMA generally affects the muscles closest to the center of the body (proximal muscles) more than the muscles further away (distal muscles).
The predominant symptom of SMA caused by chromosome 5 (SMN-related) is voluntary muscular weakness. The muscles closest to the center of the body, such as the shoulders, hips, thighs, and upper back, are the most impacted. Deep tendon reflexes appear to be more impaired in the lower limbs than in the upper limbs.
If the muscles that control breathing and swallowing are compromised, this might lead to anomalies in these actions. Spinal curvatures can develop if the back muscles weaken.
In chromosome 5-related SMA, there is a lot of heterogeneity in the age of onset and the amount of motor function achieved. These are broadly connected with the amount of functional SMN protein present in motor neurons, which is correlated with the number of copies of SMN2 genes a person possesses. In chromosome-5 SMA, sensory, mental, and emotional functioning are all normal.
Some types of SMA aren’t caused by a lack of chromosome 5 or SMN. The severity of these kinds, as well as the muscles that are most affected, varies widely. While most forms, such as the chromosome 5-related form, affect predominantly the proximal muscles, other forms, at least in the beginning, impact mostly the distal muscles (those further distant from the body’s center).
What happens as SMA progresses?
The later symptoms appear and the more SMN protein there is, the milder the disease is predicted to be in chromosome 5-related SMA. While newborns with SMA used to seldom live longer than two years, most doctors now see SMN-related SMA as a continuum and prefer not to make hard predictions regarding life expectancy or weakening based solely on the age of start.
The most common genetic cause of infant mortality is SMA.
What is the current state of SMA research?
The focus of research has been on ways to boost the body’s synthesis of the SMN protein, which is missing in the chromosome 5-related variants of the disease. Methods to aid motor neurons in surviving in harsh conditions are among the approaches.
The US Food and Drug Administration (FDA) approved Spinraza (nusinersen) for the treatment of SMA on December 23, 2016. Spinraza is designed to treat the underlying abnormality in SMA, which means it has the potential to delay, stop, or even reverse the symptoms of the disease.
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