About spinal muscular atrophy type 1

What is spinal muscular atrophy type 1?

The spinal muscular atrophies (SMAs), are characterized by degeneration of nerve cells (motor nuclei) within the lowest region of the brain (lower brainstem) and certain motor neurons in the spinal cord (anterior horn cells) leading to muscle weakness of the truncal, and extremity muscles initially, followed by chewing, swallowing and breathing difficulties. Motor neurons are nerve cells that transmit nerve impulses from the spinal cord or brain (central nervous system) to muscle or glandular tissue.

Approximately 80 percent of individuals with SMA fall into the severe category (Werdnig-Hoffman disease or SMA1). Infants with SMA1 experience severe weakness before 6 months of age, and the patient never achieves the ability to sit independently when placed. Muscle weakness, lack of motor development and poor muscle tone are the major clinical manifestations of SMA1. Infants with the gravest prognosis have problems sucking or swallowing. Some show abdominal breathing in the first few months of life. Abdominal breathing is noted when the abdomen protrudes during inspiration. Normally, the chest expands during inspiration as the intercostal muscles (the muscles between the ribs) expand during inspiration. Abdominal breathing occurs when the intercostal muscles are weak and the diaphragm muscle is responsible for inspiration. Movement of the diaphragm (the muscle between the chest and abdomen) expands causing the abdomen to move during the inspiration cycle. Twitching of the tongue is often seen (fasciculations). Cognitive development is normal. Most affected children die before 2 years of age but survival may be dependent on the degree of respiratory function and respiratory support.

The different subtypes, SMA 0-4 are based on the age of onset of symptoms and the course and progression of the disease. SMA represents a continuum or spectrum of disease with a mild end and a severe end. SMA0 patients are extremely weak at birth, require immediate artificial ventilation and will never breathe independently. Werdnig-Hoffman disease, which is also known as spinal muscular atrophy type 1 (SMA1) or acute spinal muscular atrophy, refers to individuals who have symptom onset prior to 6 months of age. SMA 2 patients will show symptoms prior to age 1 year, will sit but never walk. SMA 3 patients (Kugelberg-Welander disease) will show symptoms after age 1, and will walk for a period of time prior to loss of motor abilities. SMA 4 patients will not develop symptoms much before age 10 years.

All the SMAs are inherited as an autosomal recessive trait. Molecular genetic testing has revealed that all types of autosomal recessive SMA are caused by disruptions or errors (mutations) in the SMN1 (survival motor neuron 1) gene on chromosome 5.

What are the symptoms for spinal muscular atrophy type 1?

Babies with type 1 sma have trouble sucking and swallowing symptom was found in the spinal muscular atrophy type 1 condition

Type 1. This is also a severe type of SMA. A child may not be able to support their head or sit without help. They may have floppy arms and legs and problems swallowing.

The biggest concern is weakness in the muscles that control breathing. Most children with type 1 SMA don't live past age 2 because of breathing problems.

Keep in touch with your medical team, family members, clergy, and others who can help give you the emotional support you need while your child fights this disease.

What are the causes for spinal muscular atrophy type 1?

All four types of SMA result from a deficiency of a protein called SMN, which stands for “survival of motor neuron.” Motor neurons are nerve cells in the spinal cord that are responsible for sending out signals to our muscles.

When a mutation (mistake) occurs in both copies of the SMN1 gene (one on each of your two copies of chromosome 5), it leads to a deficiency in SMN protein. If little or no SMN protein is produced, it leads to motor function problems.

Genes that neighbor SMN1, called SMN2 genes, are similar in structure to SMN1 genes. They can sometimes help offset the SMN protein deficiency, but the number of SMN2 genes fluctuates from person to person. So the type of SMA depends on how many SMN2 genes a person has to help make up for their SMN1 gene mutation. If a person with chromosome 5–related SMA has more copies of the SMN2 gene, they can produce more working SMN protein. In return, their SMA will be milder with a later onset than someone who has fewer copies of the SMN2 gene.

What are the treatments for spinal muscular atrophy type 1?

The FDA has approved three medications to treat SMA: nusinersen (Spinraza), onasemnogene abeparvovec-xioi (Zolgensma) and risdiplam (Evrysdi). Both are forms of gene therapy that affect the genes involved in SMA. The SMN1 and SMN2 genes give your body instructions for making a protein that helps with controlling muscle movement.

  • Nusinersen (Spinraza). This treatment adjusts the SMN2 gene and lets it make more protein. It's used for both children and adults with SMA. Your child's medical team will inject the drug into the fluid around their spinal cord. Including preparation and recovery time, this can take at least 2 hours and will need to be done several times, followed by another dose every 4 months. Studies show it helps about 40% of people who use it by making them stronger and slowing the disease.
  • Onasemnogene abeparvovec-xioi (Zolgensma). This involves replacing the problem SMN1 gene. It's used for children under 2 years old. Your child's medical team will put a tiny tube called a catheter directly into a vein in their arm or hand (an IV). Then, they'll send a copy of the SMN gene through the tube into a specific group of motor neuron cells. This will need to be done only one time. In studies, onasemnogene abeparvovec-xioi helped children with SMA reach certain developmental milestones faster, like controlling their heads or sitting without support.
  • Risdiplam (Evrysdi). This treatment works to stop the SMN2 genes from disrupting the protein production,  allowing the protein to reach the nerve cells as needed. Your child takes it orally once a day after a meal. The dosage is determined by their weight.Clinical trials showed improved muscle function after 12 months in 41% of those taking it.

What are the risk factors for spinal muscular atrophy type 1?

SMA is a disease that's passed down through families. If your child has SMA, it's because they have two copies of a broken gene, one from each parent.

Is there a cure/medications for spinal muscular atrophy type 1?

Werdnig-Hoffmann disease, also known as spinal muscular atrophy type 1 (SMA1), is a hereditary neuromuscular condition that damages the nerve cells that regulate voluntary muscles.

  • Without therapy, SMA1 symptoms, which include increased muscle weakness and poor muscle tone as a result of the death of lower motor neurons in the spinal cord and brain stem, become visible before the age of six months.
  • Breathing and feeding issues could also be present.
  • SMA1 is an autosomal recessive disease that is brought on by mutations in the SMN1 gene.
  • SMA1 can be diagnosed if symptoms are present, and genetic testing can confirm the diagnosis.
  • In order to identify SMA before symptoms appear, it has been added to the list of recommended newborn screening tests in the United States.
  • There's currently no cure for SMA type 1, but the Food and Drug Administration (FDA) has recently approved several new treatments.


  • The SMA type 1 condition is irreversible.
  • Treatments are based on the symptoms and kind of SMA.
  • Physical and occupational therapy, as well as assistive tools including orthopaedic braces, crutches, walkers, and wheelchairs, are helpful for many SMA patients.
  • A one-time intravenous (IV) infusion of the medication onasemnogene abeparvovec-xioi (Zolgensma) may be beneficial for children under the age of two. Through this treatment, a defective or absent SMN1 gene is replaced.

Babies with type 1 SMA have trouble sucking and swallowing, They don't reach common developmental milestones like sitting or holding their heads up, muscular tone issues and weakness,Breathing and feeding issues could also be present
A hereditary disorder called spinal muscular atrophy (SMA) weakens the muscles and impairs movement,Although the problem is serious and only grows worse with time, there are therapies to assist control the symptoms
Nusinersen (Spinraza),Onasemnogene abeparvovec-xioi (Zolgensma),Risdiplam (Evrysdi)

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