BACK TOTOP Browse A-ZSearchBrowse A-ZABCDEFGHIJKLMNOPQRSTUVWXYZ0-9 E-mail FormEmail ResultsName:Email address:Recipients Name:Recipients address:Message: Print-FriendlyBookmarksbookmarks-menuSpinal muscular atrophyWerdnig-Hoffmann disease; Kugelberg-Welander diseaseSpinal muscular atrophy (SMA) is a group of disorders of the motor neurons (motor cells). These disorders are passed down through families (inherited) and can appear at any stage of life. The disorder leads to muscle weakness and atrophy. Causes SMA is a collection of different motor nerve (or neuron) diseases. The disease is caused by a lack of a protein (SMN) due to defective genes.Most of the time, a person must get one copy of the defective gene from both parents to be affected. The most severe form is SMA type I, also called Werdnig-Hoffman disease. Infants with SMA type II have less severe symptoms during early infancy, but they become weaker with time. SMA type III is a less severe form of the disease.In rare cases, SMA begins in adulthood. This is the mildest form of the disease.A family history of SMA in an immediate family member (such as brother or sister) is a risk factor for all types of the disorder. Symptoms Symptoms of SMA may vary depending on the SMA type.Infants with SMA type I are born with very little muscle tone, weak muscles, and feeding and breathing problems. In infants with SMA type II, symptoms may not appear until age 6 months to 2 years. Type III SMA is a milder disease that starts in childhood or adolescence and slowly gets worse. Type IV is even milder, with weakness starting in adulthood.Often, weakness is first felt in the shoulder and leg muscles. Weakness gets worse over time and eventually becomes severe.WeaknessWeakness is reduced strength in one or more muscles.Read Article Now Book Mark Article Symptoms in an infant:Breathing difficulty with shortness of breath and labored breathing, leading to a lack of oxygen Feeding difficulty (food may go into the windpipe instead of the stomach) Floppy infant (poor muscle tone) Lack of head control Little movement Weakness that gets worseSymptoms in a child:Frequent, increasingly severe respiratory infections Nasal speech Posture that gets worseWith SMA, the nerves that control feeling (sensory nerves) are not affected. So, a person with the disease can feel things normally. Exams and Tests The health care provider will take a careful history and perform a brain/nervous system (neurologic) examination to find out if there is:A family history of neuromuscular disease Floppy (flaccid) muscles No deep tendon reflexes Twitches of the tongue muscleTests that may be ordered include:Aldolase blood test Aldolase blood testAldolase is a protein (called an enzyme) that helps break down certain sugars to produce energy. It is found in high amount in muscle and liver tiss...ImageRead Article Now Book Mark Article Erythrocyte sedimentation rate (ESR) Erythrocyte sedimentation rateESR stands for erythrocyte sedimentation rate. It is commonly called a "sed rate. "It is a test that indirectly measures the level of certain protei...ImageRead Article Now Book Mark Article Creatine phosphate kinase blood test Creatine phosphate kinase blood testCreatine phosphokinase (CPK) is an enzyme in the body. It is found mainly in the heart, brain, and skeletal muscle. This article discusses the test...ImageRead Article Now Book Mark Article DNA testing to confirm diagnosis Electromyography (EMG) ElectromyographyElectromyography (EMG) is a test that checks the health of the muscles and the nerves that control the muscles.ImageRead Article Now Book Mark Article Lactate/pyruvate ratio in the blood MRI of the brain, spine, and spinal cord MRIA magnetic resonance imaging (MRI) scan is an imaging test that uses powerful magnets and radio waves to create pictures of the body. It does not us...ImageRead Article Now Book Mark Article Muscle biopsy Muscle biopsyA muscle biopsy is the removal of a small piece of muscle tissue for examination.ImageRead Article Now Book Mark Article Nerve conduction study Nerve conduction studyNerve conduction velocity (NCV) is a test to see how fast electrical signals move through a nerve. This test is done along with electromyography (EM...ImageRead Article Now Book Mark Article Amino acid blood tests Lung function tests Swallowing study Thyroid-stimulating hormone (TSH) blood testThyroid-stimulating hormoneA TSH test measures the amount of thyroid stimulating hormone (TSH) in your blood. TSH is produced by the pituitary gland. It prompts the thyroid g...ImageRead Article Now Book Mark Article Treatment There is no treatment to cure SMA. However, there are now three drugs approved by the FDA that slow how fast the muscle weakness progresses:Onasemnogene abeparvovec-xioi (Zolgensma) Risdiplam (Evrysdi) Nusinersen (Spinraza)These drugs work by increasing the amount of the SMN protein produced. Talk with your provider to see if either of these medicines is right for you or your child.Supportive care is important. Breathing complications are common in the more severe forms of SMA. To help with breathing, a device or machine called a ventilator may be needed.People with SMA also need to be watched for choking. This is because the muscles that control swallowing are weak.Physical therapy is important to prevent contractions of muscles and tendons and abnormal curvature of the spine (scoliosis). Bracing may be needed. Surgery may be needed to correct skeletal deformities, such as scoliosis.ScoliosisScoliosis is an abnormal curving of the spine. Your spine is your backbone. It runs straight down your back. Everyone's spine naturally curves a b...ImageRead Article Now Book Mark Article Outlook (Prognosis) Without treatment, children with SMA type I rarely live longer than 2 to 3 years because of respiratory problems and infections. Survival time with type II is longer, but the disease kills most of those who are affected while they are still children. New therapies that increase the amount of SMN protein have resulted in infants and children living much longer.Children with type III disease may survive into early adulthood. But, people with all forms of the disease have weakness and disability that gets worse over time. Adults who develop SMA often have a normal life expectancy. Possible Complications Complications that may result from SMA include:Aspiration (food and fluids get into the lungs, causing pneumonia) AspirationAspiration means to draw in or out using a sucking motion. It has two meanings:Breathing in a foreign object (for example, sucking food into the air...ImageRead Article Now Book Mark Article Contractions of muscles and tendons Heart failure Scoliosis When to Contact a Medical Professional Contact your provider if your child:Appears weak Develops any other symptoms of SMA Has difficulty feedingBreathing difficulty can rapidly become an emergency condition.Breathing difficultyBreathing difficulty may involve:Difficult breathing Uncomfortable breathingFeeling like you are not getting enough airImageRead Article Now Book Mark Article Prevention Genetic counseling is recommended for people with a family history of SMA who want to have children.Genetic counselingGenetics is the study of heredity, the process of a parent passing certain genes on to their children. A person's appearance, such as height, hair co...ImageRead Article Now Book Mark Article Open ReferencesReferencesFearon C, Murray B, Mitsumoto H. Disorders of upper and lower motor neurons. In: Jankovic J, Mazziotta JC, Pomeroy SL, Newman NJ, eds. Bradley and Daroff's Neurology in Clinical Practice. 8th ed. Philadelphia, PA: Elsevier; 2022:chap 97.Manzur AY. Evaluation and investigation of neuromuscular disorders. In: Kliegman RM, St. Geme JW, Blum NJ, Shah SS, Tasker RC, Wilson KM, eds. Nelson Textbook of Pediatrics. 22nd ed. Philadelphia, PA: Elsevier; 2025:chap 647.NIH-National Institute of Neurological Disorders and Stroke website. Spinal muscular atrophy. www.ninds.nih.gov/health-information/disorders/spinal-muscular-atrophy. Updated November 28, 2023. Accessed March 14, 2024.AllVideoImagesTogSuperficial anterior muscles - illustration Superficial muscles are close to the surface of the skin. Muscles which lie closer to bone or internal organs are called deep muscles.Superficial anterior musclesillustrationScoliosis - illustration Abnormal curvature in the spine is known as scoliosis, and generally begins just at the onset of puberty and progresses during the period of rapid growth. Most junior high schools routinely screen for scoliosis because, if caught early, progressive spine curvature can be prevented. Scoliosis affects girls much more frequently than boys.ScoliosisillustrationSuperficial anterior muscles - illustration Superficial muscles are close to the surface of the skin. Muscles which lie closer to bone or internal organs are called deep muscles.Superficial anterior musclesillustrationScoliosis - illustration Abnormal curvature in the spine is known as scoliosis, and generally begins just at the onset of puberty and progresses during the period of rapid growth. Most junior high schools routinely screen for scoliosis because, if caught early, progressive spine curvature can be prevented. Scoliosis affects girls much more frequently than boys.ScoliosisillustrationRelated Information Autosomal recessive(Special Topic)Hypotonia(Symptoms)Weakness(Symptoms)Proximal(Special Topic)Aspiration(Special Topic) Review Date: 12/31/2023 Reviewed By: Joseph V. Campellone, MD, Department of Neurology, Cooper Medical School at Rowan University, Camden, NJ. Review provided by VeriMed Healthcare Network. Also reviewed by David C. Dugdale, MD, Medical Director, Brenda Conaway, Editorial Director, and the A.D.A.M. Editorial team. The information provided herein should not be used during any medical emergency or for the diagnosis or treatment of any medical condition. A licensed medical professional should be consulted for diagnosis and treatment of any and all medical conditions. 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Spinal muscular atrophyWerdnig-Hoffmann disease; Kugelberg-Welander diseaseSpinal muscular atrophy (SMA) is a group of disorders of the motor neurons (motor cells). These disorders are passed down through families (inherited) and can appear at any stage of life. The disorder leads to muscle weakness and atrophy. Causes SMA is a collection of different motor nerve (or neuron) diseases. The disease is caused by a lack of a protein (SMN) due to defective genes.Most of the time, a person must get one copy of the defective gene from both parents to be affected. The most severe form is SMA type I, also called Werdnig-Hoffman disease. Infants with SMA type II have less severe symptoms during early infancy, but they become weaker with time. SMA type III is a less severe form of the disease.In rare cases, SMA begins in adulthood. This is the mildest form of the disease.A family history of SMA in an immediate family member (such as brother or sister) is a risk factor for all types of the disorder. Symptoms Symptoms of SMA may vary depending on the SMA type.Infants with SMA type I are born with very little muscle tone, weak muscles, and feeding and breathing problems. In infants with SMA type II, symptoms may not appear until age 6 months to 2 years. Type III SMA is a milder disease that starts in childhood or adolescence and slowly gets worse. Type IV is even milder, with weakness starting in adulthood.Often, weakness is first felt in the shoulder and leg muscles. Weakness gets worse over time and eventually becomes severe.WeaknessWeakness is reduced strength in one or more muscles.Read Article Now Book Mark Article Symptoms in an infant:Breathing difficulty with shortness of breath and labored breathing, leading to a lack of oxygen Feeding difficulty (food may go into the windpipe instead of the stomach) Floppy infant (poor muscle tone) Lack of head control Little movement Weakness that gets worseSymptoms in a child:Frequent, increasingly severe respiratory infections Nasal speech Posture that gets worseWith SMA, the nerves that control feeling (sensory nerves) are not affected. So, a person with the disease can feel things normally. Exams and Tests The health care provider will take a careful history and perform a brain/nervous system (neurologic) examination to find out if there is:A family history of neuromuscular disease Floppy (flaccid) muscles No deep tendon reflexes Twitches of the tongue muscleTests that may be ordered include:Aldolase blood test Aldolase blood testAldolase is a protein (called an enzyme) that helps break down certain sugars to produce energy. It is found in high amount in muscle and liver tiss...ImageRead Article Now Book Mark Article Erythrocyte sedimentation rate (ESR) Erythrocyte sedimentation rateESR stands for erythrocyte sedimentation rate. It is commonly called a "sed rate. "It is a test that indirectly measures the level of certain protei...ImageRead Article Now Book Mark Article Creatine phosphate kinase blood test Creatine phosphate kinase blood testCreatine phosphokinase (CPK) is an enzyme in the body. It is found mainly in the heart, brain, and skeletal muscle. This article discusses the test...ImageRead Article Now Book Mark Article DNA testing to confirm diagnosis Electromyography (EMG) ElectromyographyElectromyography (EMG) is a test that checks the health of the muscles and the nerves that control the muscles.ImageRead Article Now Book Mark Article Lactate/pyruvate ratio in the blood MRI of the brain, spine, and spinal cord MRIA magnetic resonance imaging (MRI) scan is an imaging test that uses powerful magnets and radio waves to create pictures of the body. It does not us...ImageRead Article Now Book Mark Article Muscle biopsy Muscle biopsyA muscle biopsy is the removal of a small piece of muscle tissue for examination.ImageRead Article Now Book Mark Article Nerve conduction study Nerve conduction studyNerve conduction velocity (NCV) is a test to see how fast electrical signals move through a nerve. This test is done along with electromyography (EM...ImageRead Article Now Book Mark Article Amino acid blood tests Lung function tests Swallowing study Thyroid-stimulating hormone (TSH) blood testThyroid-stimulating hormoneA TSH test measures the amount of thyroid stimulating hormone (TSH) in your blood. TSH is produced by the pituitary gland. It prompts the thyroid g...ImageRead Article Now Book Mark Article Treatment There is no treatment to cure SMA. However, there are now three drugs approved by the FDA that slow how fast the muscle weakness progresses:Onasemnogene abeparvovec-xioi (Zolgensma) Risdiplam (Evrysdi) Nusinersen (Spinraza)These drugs work by increasing the amount of the SMN protein produced. Talk with your provider to see if either of these medicines is right for you or your child.Supportive care is important. Breathing complications are common in the more severe forms of SMA. To help with breathing, a device or machine called a ventilator may be needed.People with SMA also need to be watched for choking. This is because the muscles that control swallowing are weak.Physical therapy is important to prevent contractions of muscles and tendons and abnormal curvature of the spine (scoliosis). Bracing may be needed. Surgery may be needed to correct skeletal deformities, such as scoliosis.ScoliosisScoliosis is an abnormal curving of the spine. Your spine is your backbone. It runs straight down your back. Everyone's spine naturally curves a b...ImageRead Article Now Book Mark Article Outlook (Prognosis) Without treatment, children with SMA type I rarely live longer than 2 to 3 years because of respiratory problems and infections. Survival time with type II is longer, but the disease kills most of those who are affected while they are still children. New therapies that increase the amount of SMN protein have resulted in infants and children living much longer.Children with type III disease may survive into early adulthood. But, people with all forms of the disease have weakness and disability that gets worse over time. Adults who develop SMA often have a normal life expectancy. Possible Complications Complications that may result from SMA include:Aspiration (food and fluids get into the lungs, causing pneumonia) AspirationAspiration means to draw in or out using a sucking motion. It has two meanings:Breathing in a foreign object (for example, sucking food into the air...ImageRead Article Now Book Mark Article Contractions of muscles and tendons Heart failure Scoliosis When to Contact a Medical Professional Contact your provider if your child:Appears weak Develops any other symptoms of SMA Has difficulty feedingBreathing difficulty can rapidly become an emergency condition.Breathing difficultyBreathing difficulty may involve:Difficult breathing Uncomfortable breathingFeeling like you are not getting enough airImageRead Article Now Book Mark Article Prevention Genetic counseling is recommended for people with a family history of SMA who want to have children.Genetic counselingGenetics is the study of heredity, the process of a parent passing certain genes on to their children. A person's appearance, such as height, hair co...ImageRead Article Now Book Mark Article Open ReferencesReferencesFearon C, Murray B, Mitsumoto H. Disorders of upper and lower motor neurons. In: Jankovic J, Mazziotta JC, Pomeroy SL, Newman NJ, eds. Bradley and Daroff's Neurology in Clinical Practice. 8th ed. Philadelphia, PA: Elsevier; 2022:chap 97.Manzur AY. Evaluation and investigation of neuromuscular disorders. In: Kliegman RM, St. Geme JW, Blum NJ, Shah SS, Tasker RC, Wilson KM, eds. Nelson Textbook of Pediatrics. 22nd ed. Philadelphia, PA: Elsevier; 2025:chap 647.NIH-National Institute of Neurological Disorders and Stroke website. Spinal muscular atrophy. www.ninds.nih.gov/health-information/disorders/spinal-muscular-atrophy. Updated November 28, 2023. Accessed March 14, 2024.