Lexi Webster
Spinal muscular atrophy (SMA) is a genetic condition that causes muscle weakness and can be fatal. While there is no cure for SMA, there are now treatments available that can improve muscle function and life expectancy. In Australia, there is a growing population of children and adults living with SMA, and the healthcare system is working to provide support and improve health outcomes for those affected.
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What You'll Learn
SMA is a genetic disease that causes muscle weakness
Spinal muscular atrophy (SMA) is a genetic disease that causes muscle weakness. It affects the nerves that lead to the muscles, known as motor neurons. Over time, the muscles become weaker and waste away. SMA is the childhood version of motor neurone disease.
SMA is associated with homozygous variants in the Survival Motor Neuron 1 (SMN1) gene located on chromosome 5q13. Almost all patients (>95%) with the most common forms of SMA have deletions of SMN1 exon 7; the loss of exon 7 abolishes the production of SMN1 protein. Most other cases of SMA are associated with an SMN1 gene variant causing loss of exon 7 in combination with a variant in the other copy of SMN1 that markedly reduces or eliminates production of SMN1 protein. In rare cases, SMA can be caused by pathogenic variants in other genes, so-called “non-5q SMA”, and more than 16 genes have been implicated.
There are five types of SMA, based on the age when symptoms first appear. The age at which SMA symptoms begin roughly correlates with the degree to which motor function is affected: the earlier the age of onset, the greater the impact on motor function. SMA type 1 (infantile-onset SMA or Werdnig-Hoffman disease) is the most common form of SMA. It usually becomes evident before 6 months of age. Symptoms include severe muscle weakness and trouble breathing, coughing, and swallowing. Some children with SMA type 1 will die before their second birthday, but aggressive therapy is improving the outlook for these children. Type ll is usually first noticed between 6 and 18 months of age. Children with this type of SMA can sit without support but are unable to stand or walk without help. Type lll (also known as Kugelberg-Welander disease) shows symptoms after 18 months of age. Children can walk independently but may have difficulty doing so. They may also have trouble running, rising from a chair, or climbing stairs. Type 4 (adult SMA) rarely impacts a patient's lifespan.
There is no cure for SMA, but there are new treatments available that can improve muscle function and life expectancy. For example, newborns with SMA can be started on treatment before symptoms appear, improving their functioning and survival. Three medicines are currently available in Australia that can help slow or stop the progression of SMA. These treatments are not considered a cure for SMA, but they may improve muscle function and life expectancy.
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There is no cure, but treatments are available
Spinal muscular atrophy (SMA) is a genetic disease that causes muscles to weaken. It affects the nerves leading to the muscles, called motor neurons. SMA is the childhood version of motor neurone disease. Although there is no cure for SMA, there are treatments available that can improve muscle function and life expectancy.
SMA is associated with homozygous variants in the Survival Motor Neuron 1 (SMN1) gene. Individuals with SMA do not produce survival motor neuron (SMN) protein in high enough levels. Without this protein, motor neuron cells shrink and eventually die, causing debilitating and potentially fatal muscle weakness. One way to treat SMA is to increase the amount of SMN protein in the body. This is often called an "SMN-based" or "SMN-enhancing" approach.
There are several treatments available for SMA. Three medicines are currently available in Australia that can help slow or stop the progression of SMA. These include a gene replacement therapy called Zolgensma, and two drugs, nusinersen (Spinraza) and risdiplam (Evrysdi). All three treatments have been approved by the U.S. Food and Drug Administration (FDA). Additionally, there is another drug, onasemnogene abeparvovec, which has been approved through accelerated assessment procedures.
It is important that individuals with SMA begin therapy as soon after diagnosis as possible. This is especially critical for SMN-enhancing therapies. Beginning therapy early is the only way to prevent or slow down motor neuron loss. For babies identified through newborn screening, treatment should begin before symptoms appear.
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SMA is the childhood version of motor neurone disease
Spinal muscular atrophy (SMA) is a genetic condition that affects the nerves leading to the muscles, known as motor neurons. SMA is the childhood version of motor neurone disease. It is a physical condition and does not affect a person's intelligence. SMA is a neuromuscular disorder that causes certain muscles to become weak and waste away. It is the second most common severe hereditary disease of infancy and childhood after cystic fibrosis, affecting between 1 in 6,000 to 1 in 11,000 live births. SMA is about twice as common in white and Asian people as in Black and Hispanic people.
SMA involves the loss of nerve cells called motor neurons in the spinal cord and is classified as a motor neuron disease. The most common form of SMA is chromosome 5-related, or SMN-related. This form of SMA is caused by a deficiency of a motor neuron protein called SMN, which is necessary for normal motor neuron function. SMN plays a pivotal role in gene expression in motor neurons. Its deficiency is caused by genetic flaws (mutations) on chromosome 5 in a gene called SMN1. The most common mutation in the SMN1 gene within patients diagnosed with SMA is a deletion of a whole segment, called exon 7. Almost all patients (>95%) with the most common forms of SMA have deletions of SMN1 exon 7.
There are five subtypes of SMA, classified based on the age of onset, severity, and life expectancy. SMA type 0 is a rare subtype that affects a fetus before birth, with severe muscle weakness and typically resulting in respiratory failure and death at birth or within the first month of life. About 60% of SMA cases are type 1, also called Werdnig-Hoffman disease. Children with type 1 rarely live beyond three years of age. In type 3, the main symptom is progressive muscle weakness that affects the legs more than the arms. The main symptom of type 4 is mild leg weakness. Type II has a slower disease progression, and death before the age of 20 is frequent. Type III has a normal or near-normal life expectancy if standards of care are followed. Type IV, adult-onset SMA, usually only impairs mobility and does not affect life expectancy.
While there is no cure for SMA, there are new treatments available that can slow or stop the progression of the disease. These treatments include three medicines available in Australia that may improve muscle function and life expectancy. Additionally, newborns with SMA can be started on treatment before symptoms appear, improving their functioning and survival. Management of SMA depends on current symptoms, and a multidisciplinary healthcare team is recommended to support individuals with SMA. This team can include a general practitioner (GP), neurologist, nurses, paediatrician, physiotherapist, occupational therapist, and speech therapist.
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SMA is a neuromuscular disorder
Spinal muscular atrophy (SMA) is a genetic disease affecting the central nervous system, peripheral nervous system, and voluntary muscle movement. SMA is classified as a motor neuron disease. It involves the loss of nerve cells called motor neurons in the spinal cord and brain, which control muscle movement. These motor neurons are also known as lower motor neurons or anterior horn cells. Without these motor neurons, muscles do not receive nerve signals, causing them to waste away (atrophy). SMA is muscular because its primary effect is on muscles.
SMA is typically inherited and occurs when an affected individual inherits two mutated genes, one from each parent. This is known as an autosomal recessive disorder. Those who inherit only one mutated gene are carriers of the disease but do not exhibit any symptoms. SMA can also arise sporadically without inheriting two mutated genes, but this is extremely rare. SMA is often caused by genetic flaws (mutations) on chromosome 5, specifically in the SMN1 gene, which is responsible for producing the SMN protein. This protein is critical for the health and function of motor neurons.
There are five types of SMA based on the age when symptoms first appear and the severity of symptoms. Type 1 SMA, also called Werdnig-Hoffman disease, is the most common, accounting for about 60% of cases. Symptoms of type 1 SMA appear within the first six months of life and include limited head control, decreased muscle tone, and difficulty swallowing and breathing. Without breathing support, children with type 1 SMA rarely live beyond three years of age. Type 2 SMA, or Dubowitz disease, has symptoms appearing between six and 18 months of life, including worsening muscle weakness that affects the legs more than the arms. Type 0 SMA is a rare subtype that affects fetuses before birth, causing severe muscle weakness and respiratory failure at birth or within the first month of life. Type 3 and Type 4 SMA are later-onset forms with less severe courses, generally correlating with higher levels of motor function.
While there is currently no cure for SMA, new treatments are available in Australia that can slow or stop the disease's progression and improve muscle function and life expectancy. These treatments include medicines and a multidisciplinary healthcare team approach, including general practitioners, neurologists, nurses, paediatricians, physiotherapists, and other specialists.
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SMA patients require multidisciplinary healthcare teams
Spinal muscular atrophy (SMA) is a genetic condition that causes muscles to weaken and waste away over time. It affects the nerves leading to the muscles, known as motor neurons. SMA is the childhood version of motor neurone disease. There is no cure for SMA, but there are new treatments available that can slow or stop its progression and improve muscle function and life expectancy.
SMA patients require a multidisciplinary healthcare team to support them throughout their journey with the condition. This team should consist of clinicians from a variety of backgrounds who work together within their areas of specialty to improve the health and functioning of the patient. The team should include a neurologist, who generally coordinates care as they are most aware of the disease course and potential issues. Other specialists involved in the care of SMA patients include pulmonologists, orthopedic surgeons, physiatrists, paediatricians, physiotherapists, occupational therapists, and speech therapists.
The multidisciplinary team can offer personalized care plans and innovative treatments to SMA patients. For example, Massachusetts General Hospital offers comprehensive care tailored to the unique needs of adults living with SMA. Their spinal muscular atrophy program brings together specialists from diverse fields to address the complexities of the condition. During clinical visits, patients are cared for by a core team that includes neurology providers, nurses, physical therapists, and speech language pathologists. The hospital also offers consultations with experts from other specialties, including endocrinology, gastroenterology, genetic counseling, interventional radiology, nutrition, obstetrics and gynecology, orthopedics, pulmonology, respiratory therapy, and urology.
SMA Australia emphasizes the importance of a multidisciplinary healthcare team that includes a General Practitioner (GP), a neurologist, and nurses and other healthcare professionals with experience in SMA. They also suggest that patients may require treatment for related conditions, including sleep disturbances, breathing difficulties, and bone health issues.
The benefits of a multidisciplinary approach to SMA patient care include improved patient outcomes, enhanced quality of life, and effective management of every aspect of a patient's health. This collaborative model allows individual parts of the patient's functioning to be addressed by experts in those areas.
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Frequently asked questions
SMA is a rare disease, with about 1 in 11,000 people being born with it in the United States. While the prevalence in Australia is unknown, it is likely to be similar.
SMA stands for spinal muscular atrophy. It is a genetic condition that causes muscles to become weaker over time due to the effects on nerves called motor neurons.
While there is currently no cure for SMA, there are new treatments available that can slow or stop the progression of the disease and improve muscle function and life expectancy. These include three medicines available in Australia.
SMA is diagnosed through genetic testing, typically via a simple blood test. Other conditions besides SMA are also tested for, as the symptoms of other diseases may be similar.
SMA is a recessive genetic disorder, which means that for a child to have SMA, both parents must be carriers of the faulty SMN gene. In this case, there is a 25% chance of their child being born with SMA.
