Spinal Muscular Atrophy (SMA)

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MedlinePlus: ⁴¹ What is spinal muscular atrophy (SMA)? Spinal muscular atrophy (SMA) is a group of genetic diseases that damages and kills motor neurons. Motor neurons are a type of nerve cell in the spinal cord and lower part of the brain. They control movement in your arms, legs, face, chest, throat, and tongue. As the motor neurons die off, your muscles start to weaken and atrophy (waste away). The muscle damage gets worse over time and can affect speaking, walking, swallowing, and breathing. What are the types of spinal muscular atrophy (SMA) and what are their symptoms? There are different types of SMA. They are based on how serious the disease is and when the symptoms start: Type l is also called Werdnig-Hoffman disease or infantile-onset SMA. It is the most severe type. It is also the most common. Babies with this type usually show signs of the disease before 6 months of age. In more severe cases, the signs show up even before or just after birth (Types 0 or 1A). The babies may have trouble swallowing and breathing and may not move around a lot. They have chronic shortening of muscles or tendons (called contractures). They usually cannot sit up without help. Without treatment, many children with this type will die before 2 years of age. Type ll is a moderate to severe type of SMA. It usually first noticed between 6 and 18 months of age. Most children with this type can sit without support but cannot stand or walk without help. They may also have trouble breathing. They can usually live into adolescence or young adulthood. Type lll is also called Kugelberg-Welander disease. It is the mildest type that affects children. The signs of the disease usually show up after age 18 months. Children with this type can walk by themselves but may have trouble running, getting up from a chair, or climbing stairs. They may also have scoliosis (curvature of the spine), contractures, and respiratory infections. With treatment, most children with this type will have a normal lifespan. Type IV is rare and often mild. It usually causes symptoms after 21 years of age. The symptoms include mild to moderate leg muscle weakness, tremors, and mild breathing problems. The symptoms slowly get worse over time. People with this type of SMA have a normal lifespan. What causes spinal muscular atrophy (SMA)? Most types of SMA are caused by a change in the SMN1 gene. This gene is responsible for making a protein that the motor neurons need to be healthy and to function. But when part of the SMN1 gene is missing or abnormal, there isn't enough protein for the motor neurons. This causes the motor neurons to die off. Most people have two copies of the SM1 gene - one from each parent. SMA normally only happens when both copies have the gene change. If only one copy has the change, there usually aren't any symptoms. But that gene could be passed down from parent to child. Some of the less common types of SMA may be caused by changes in other genes. How is spinal muscular atrophy (SMA) diagnosed? Your health care provider may use many tools to diagnose SMA: A physical exam A medical history, including asking about family history Genetic testing to check for the gene changes that cause SMA Electromyography and nerve conduction studies and a muscle biopsy may be done, especially if no gene changes were found Parents who have a family history of SMA may want to do a prenatal test to check to see whether their baby has an SMN1 gene change. An amniocentesis or in some cases a chorionic villi sampling (CVS) is used to get the sample for testing. In some states, genetic testing for SMA is part of newborn screening tests. What are the treatments for spinal muscular atrophy (SMA)? There is no cure for SMA. Treatments can help manage symptoms and prevent complications. They may include: Medicines to help the body make more of the proteins that the motor neurons need Gene therapy for children under 2 years of age Physical, occupational, and rehabilitation therapy to help to improve posture and the mobility of the joints. These therapies may also improve blood flow and slow muscle weakness and atrophy. Some people may also need therapy for trouble speaking, chewing, and swallowing. Assistive devices such as supports or braces, orthotics, speech synthesizers, and wheelchairs to help people stay more independent Good nutrition and a balanced diet to help maintain weight and strength. Some people might need a feeding tube in order to get the nutrition they need. Breathing support for people who have muscle weakness in the neck, throat, and chest. The support may include devices to help with breathing during the day and to prevent sleep apnea at night. Some people might need to be on a ventilator. NIH: National Institute of Neurological Disorders and Stroke

MalaCards based summary: Spinal Muscular Atrophy, also known as sma, is related to spinal muscular atrophy, distal, autosomal recessive, 1 and spinal muscular atrophy, x-linked 2, and has symptoms including tremor, back pain and headache. An important gene associated with Spinal Muscular Atrophy is SMN1 (Survival Of Motor Neuron 1, Telomeric), and among its related pathways/superpathways is SARS-CoV-2 modulates host translation machinery. The drugs Acetaminophen and Risdiplam have been mentioned in the context of this disorder. Affiliated tissues include spinal cord, skeletal muscle and tongue, and related phenotypes are nervous system and normal

MedlinePlus Genetics: ⁴² Spinal muscular atrophy is a genetic disorder characterized by weakness and wasting (atrophy) in muscles used for movement (skeletal muscles). It is caused by a loss of specialized nerve cells, called motor neurons that control muscle movement. The weakness tends to be more severe in the muscles that are close to the center of the body (proximal) compared to muscles away from the body's center (distal). The muscle weakness usually worsens with age. There are many types of spinal muscular atrophy that are caused by changes in the same genes. The types differ in age of onset and severity of muscle weakness; however, there is overlap between the types. Other forms of spinal muscular atrophy and related motor neuron diseases, such as spinal muscular atrophy with progressive myoclonic epilepsy, spinal muscular atrophy with lower extremity predominance, X-linked infantile spinal muscular atrophy, and spinal muscular atrophy with respiratory distress type 1 are caused by mutations in other genes.Spinal muscular atrophy type 0 is evident before birth and is the rarest and most severe form of the condition. Affected infants move less in the womb, and as a result they are often born with joint deformities (contractures). They have extremely weak muscle tone (hypotonia) at birth. Their respiratory muscles are very weak and they often do not survive past infancy due to respiratory failure. Some infants with spinal muscular atrophy type 0 also have heart defects that are present from birth (congenital).Spinal muscular atrophy type I (also called Werdnig-Hoffmann disease) is the most common form of the condition. It is a severe form of the disorder with muscle weakness evident at birth or within the first few months of life. Most affected children cannot control their head movements or sit unassisted. Children with this type may have swallowing problems that can lead to difficulty feeding and poor growth. They can also have breathing problems due to weakness of respiratory muscles and an abnormally bell-shaped chest that prevents the lungs from fully expanding. Most children with spinal muscular atrophy type I do not survive past early childhood due to respiratory failure.Spinal muscular atrophy type II (also called Dubowitz disease) is characterized by muscle weakness that develops in children between ages 6 and 12 months. Children with this type can sit without support, although they may need help getting to a seated position. However, as the muscle weakness worsens later in childhood, affected individuals may need support to sit. Individuals with spinal muscular atrophy type II cannot stand or walk unaided. They often have involuntary trembling (tremors) in their fingers, a spine that curves side-to-side (scoliosis), and respiratory muscle weakness that can be life-threatening. The life span of individuals with spinal muscular atrophy type II varies, but many people with this condition live into their twenties or thirties.Spinal muscular atrophy type III (also called Kugelberg-Welander disease) typically causes muscle weakness after early childhood. Individuals with this condition can stand and walk unaided, but over time, walking and climbing stairs may become increasingly difficult. Many affected individuals require wheelchair assistance later in life. People with spinal muscular atrophy type III typically have a normal life expectancy.Spinal muscular atrophy type IV is rare and often begins in early adulthood. Affected individuals usually experience mild to moderate muscle weakness, tremors, and mild breathing problems. People with spinal muscular atrophy type IV have a normal life expectancy.

NINDS: ⁵² Spinal Muscular Atrophy refers to a group of hereditary diseases that damages and kills specialized nerve cells in the brain and spinal cord (called motor neurons). Motor neurons control movement in the arms, legs, face, chest, throat, and tongue, as well as skeletal muscle activity including speaking, walking, swallowing, and breathing. The most common form of SMA is caused by an abnormal or missing gene known as the survival motor neuron gene 1 (SMN1), which is responsible for the production of a protein essential to motor neurons. This form of SMA has four types: Type l, also called Werdnig-Hoffman disease or infantile-onset SMA, is usually evident before 6 months of age. The most severely affected children will have reduced movement and chronic shortening of muscles or tendons (called contractures). Other children may have symptoms including reduced muscle tone, lack of tendon reflexes, twitching, skeletal abnormalities, and problems swallowing and feeding. Without treatment, many affected children die before age 2 years. SMA Type ll is usually first noticed between 6 and 18 months of age. Children can sit without support but are unable to stand or walk unaided. Children also may have respiratory difficulties. Life expectancy is reduced but most individuals live into adolescence or young adulthood. SMA Type lll (Kugelberg-Welander disease) is seen after age 18 months. Children can walk independently but may have difficulty walking or running, rising from a chair, or climbing stairs. Other complications may include curvature of the spine, contractures, and respiratory infections. With treatment, most individuals can have a normal lfespan. Individuals with SMA Type IV develop symptoms after age 21 years, with mild to moderate leg muscle weakness and other symptoms.

GARD: ¹⁹ Spinal muscular atrophy (SMA) is a group of genetic neuromuscular disorders that affect the nerve cells that control voluntary muscles (motor neurons). The loss of motor neurons causes progressive muscle weakness and loss of movement due to muscle wasting (atrophy). Many types of SMA mainly affect the muscles involved in walking, sitting, arm movement, and head control. Breathing and swallowing may also become difficult as the disease progresses in many types of SMA. In some types of SMA, the loss of motor neurons makes it hard to control movement of the hands and feet. SMA type 1, 2, 3, and 4 are caused by changes (pathogenic variants, also know as genetic changes) in the SMN1 gene and are inherited in an autosomal recessive manner. Extra copies of the nearby related gene, SMN2, modify the severity of SMA. There are other rarer types of SMA caused by changes in different genes. Other autosomal recessive forms include SMA with progressive myoclonic epilepsy (SMA-PME) caused by changes in the ASAH1 gene and SMA with respiratory distress 1 (SMARD1) caused by changes in the IGHMBP2 gene. X-linked forms include X-linked infantile SMA caused by changes in UBA1. Diagnosis of SMA is suspected by symptoms and confirmed by genetic testing.

Disease Ontology: ¹¹ A motor neuron disease that is a degenerative neuromuscular disease characterized by lower motor neuron degeneration associated with progressive muscle weakness and atrophy.

Wikipedia: ⁷⁵ Spinal muscular atrophy (SMA) is a rare neuromuscular disorder that results in the loss of motor neurons... more...

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