About juvenile spinal muscular atrophy

What is juvenile spinal muscular atrophy?

Kugelberg Welander syndrome is a milder type of spinal muscular atrophy. It is a rare inherited neuromuscular disorder characterized by wasting and weakness in the muscles of the arms and legs, leading to walking difficulties in, and eventual loss of ambulation. Symptoms of Kugelberg Welander syndrome occur after 12 months of age. Patients learn to walk, may fall frequently and may have trouble walking up and down stairs at 2-3 years of age; some patients will not show functional changes until the teens. The legs are more severely affected than the arms. The long-term prognosis depends on the degree of motor function attained as a child.

Kugelberg Welander syndrome is inherited as an autosomal recessive trait. Molecular genetic testing has revealed that all types of autosomal recessive SMA (Werndnig-Hoffman disease, juvenile SMA and Kugelberg-Welander disease) are caused by mutations in the SMN (survival motor neuron) gene on chromosome 5. Deletion of the NAIP (neuronal apoptosis inhibitory protein) gene that is close to the SMN gene is also associated with SMA. More patients with Werdnig Hoffman disease (SMA1) than other types of SMA have NAIP deletions. The relationship between specific mutations in the SMN gene and nearby genes and the severity of SMA is still being investigated so classification of SMA subdivisions is based on age of onset of symptoms and maximum function achieved as opposed to the genetic profile.

What are the symptoms for juvenile spinal muscular atrophy?

Symptoms vary a lot, depending on the type of SMA:

Type 0. This is the rarest and most severe form of SMA and develops while you’re still pregnant. Babies with this type of SMA move less in the womb and are born with joint problems, weak muscle tone, and Weak muscles for breathing. They often do not survive due to breathing problems.

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.

Type 2. This affects children 6-18 months old. The symptoms range from moderate to severe and usually involve the legs more than the arms. Your child may be able to sit and walk or stand with help.

What are the causes for juvenile spinal muscular atrophy?

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.

When this happens, their body won't be able to make a specific kind of protein. Without it, the cells that control muscles die.

If your child gets a faulty gene from just one of you, they won't get SMA but will be a carrier of the disease. When your child grows up, they could pass the broken gene to their own child.

What are the treatments for juvenile spinal muscular atrophy?

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 juvenile spinal muscular atrophy?

This affects children 6-18 months old.

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