About spinal muscular atrophy type 3

What is spinal muscular atrophy type 3?

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 spinal muscular atrophy type 3?

Movement problems – such as difficulty sitting up symptom was found in the spinal muscular atrophy type 3 condition

Type 3 SMA symptoms often first appear when a child is between 12 and about 18 months of age or shortly after. But some people don’t have any signs of SMA3 until after age 3, and others don’t have any physical changes until they’re teenagers or young adults.

Muscle weakness

SMA3 causes Muscle Weakness in a child’s legs, hips, shoulders, and arms. Symptoms of this disease are all related to Muscle Weakness and loss of muscle mass (wasting).

In SMA3, muscles that are closer to the center of your child’s body tend to weaken before the muscles located farther away from their core. For example, their thigh muscles may weaken before the muscles in their ankles or feet. Leg muscles weaken before muscles in their arms, shoulders, or hands.

Usually, a child’s leg muscles are weaker than muscles in their arms. Your child’s hands may weaken at some point, but most of the time, their hand muscles are still strong enough to do basic tasks like use a computer. They may not be able to do more strenuous activities or chores.

What Are the Early Symptoms of Type 3 SMA?

Children often show their first signs of SMA3 around the time they learn to walk. Some kids may be able to learn to walk or stand without help but gradually develop these signs:

  • Difficulty walking or running
  • Trouble walking up or down a flight of stairs
  • Poor balance
  • Frequent slips and falls
  • Needing help to stand up
  • Fatigue
  • Less endurance during activity
  • Struggling to rise when they’re bent over or lying flat on their back or side
  • Poor or worsening posture
  • Clumsiness

Can’t keep up. Another possible early sign of SMA3 is that you notice that your young child cannot keep up with their friends of the same age during active play or running.

Joint Contractures and foot changes. Type 3 SMA could cause your child to have tightened, stiff joints. They may have a loss of full range of motion in some of their joints, also called contractures. Most children with type 3 SMA develop foot deformities.

Lose the ability to walk. Some kids with SMA3 may gradually lose their ability to walk or stand on their own. But other children with this disease are able to learn to walk and stay independent into their teens and adult years.

Breathing Problems

After a few years of living with SMA3, many children develop breathing problems because their intracostal muscles weaken. These are the muscles between the ribs. They expand when your child breathes in air to fill their lungs and contract when they breathe out.

As these muscles weaken, your child may not be able to take full, normal breaths. They may have a weak cough. Their lungs may be underdeveloped.

eak ribcage muscles may also cause your child to occasionally gag on chewed bits of food or drinks after swallowing. They also may have shallow breathing when they’re asleep.

Breathing problems can cause children with SMA3 to have frequent, serious respiratory infections like pneumonia. Normally mild respiratory infections could be more severe in kids with this disease.

Other possible symptoms

Children with SMA3 may have weak or trembling fingers. They also may not have a knee-jerk reaction when their knee joint reflex is tested.

Weakened muscles could cause someone with SMA3 to develop kidney problems like proteinuria, or high protein in their urine. One sign of proteinuria is Swelling around their ankles, also called edema.


About half of children with SMA3 develop scoliosis, or curvature of the spine from side to side in an “S” shape. Scoliosis in SMA3 is caused by weakening of muscles that support each side of your child’s spine. Severe Scoliosis can affect breathing. Children with SMA3 typically show signs of spine curvature early.

What are the causes for spinal muscular atrophy type 3?

Spinal muscular atrophy type 3 is a genetic disease, which means that it is caused by one or more genes not working correctly.

Disease causing variants in the following gene(s) are known to cause this disease: SMN1

What are the treatments for spinal muscular atrophy type 3?

There’s no cure for any form of SMA, but there are things you can do to that may ease symptoms and potentially slow down the progression of the disease.  

Encourage them to eat a healthy diet. While it’s important to get good nutrition, there’s no evidence that a certain type of diet can help.  

But weight gain can be a problem for people with SMA3, since it can be hard for them to get enough exercise to burn calories. You may need to work with a nutritionist to make sure that your child doesn’t get too many calories. Sometimes, it’s better for them to eat frequent small meals instead of three large ones.

Stay active. It’s important that a child with SMA get as much exercise as they can do comfortably. This will help keep their joints from stiffening up and encourage flexibility. It will also help them maintain circulation and allow them to move around. One good activity is to exercise in a pool warmed to 85 to 90 F.

But while exercise is important, it’s also important not to overdo it. Some experts believe that if a patient with SMA exercises until they’re exhausted, they’ll “burn out” their remaining motor neurons.

Get physical therapy. Physical and occupational therapy can also help people with SMA maintain muscle strength and function. A physical therapist can show you and your child stretches to do to help keep muscles from shortening, which can limit joint movements. If your child needs them, a therapist can help you choose a walker or orthotics to provide support when walking or an electric scooter for them to use for longer distances. The goal is to keep them as mobile as possible for as long as possible.

If your child does develop scoliosis, the therapist can show them correct posture and how to use a brace to help prevent the condition from progressing.

A physical therapist can also teach your child respiratory exercises that can help them breathe if they come down with a respiratory infection like a cold or the flu.

During occupational therapy, your family can learn how to modify activities of daily life so that your child can stay mobile and conserve energy.

Speech therapy can also help with any swallowing difficulties that may crop up later on as the disease progresses.

Keep tabs on their respiratory health. Unlike other forms of SMA, people with type 3 have good breathing function until much later in life. Your doctor will still need to watch them closely, though, for signs of weakening respiratory muscles. 

If they begin to experience respiratory weakening, your doctor can prescribe a portable ventilation machine to use at night.

It’s also important to people with SMA3 to stay up to date on all immunizations, especially flu and COVID vaccines. People with all types of SMA are more likely to develop chest infections if they get a respiratory virus, as they are less able to clear mucus from their lungs.

Take medication. There’s no cure for SMA, but there are drugs that may slow down its progression. They work by raising the levels of survival motor neuron (SMN) protein in the body, which prevents motor neuron cells from shrinking. The three drugs that are FDA-approved for SMA are Evrysdi, Spinraza, and Zolgensma.

What are the risk factors for spinal muscular atrophy type 3?

Spinal muscular atrophy type 3 is an inherited progressive neurodegenerative disease. SMA is caused by alterations (mutations) in the genes that make proteins needed to support motor neuron function. The degree of genetic involvement determines what type of SMA you have as well as the severity of symptoms.1

Since SMA is a genetic condition, there are no specific lifestyle factors known to cause or prevent it.
Certain lifestyle risk factors have been linked to several types of motor neuron disease, but researchers don't know if any are specifically linked to SMA.13
However, there are some lifestyle factors and habits that may make it more likely you could develop complications from the condition.
Lifestyle factors that can predispose someone with SMA to complications or other health problems include:
1. Sedentary lifestyle. If you have motor weakness, inactivity can contribute to health problems, such as upper respiratory infections, constipation, and bedsores (pressure ulcers). An exercise program that's customized to your abilities can help you maintain or improve muscle function.14
2. Exposure to infectious diseases: Chronic conditions like SMA can affect your immune system. Avoiding people who are sick with contagious infections helps you avoid potentially serious complications of infectious illnesses.15
3. Unhealthy diet: A diet that's lacking in nutrition makes it harder for the body to fight infections. If the body doesn't get adequate energy from food, it may make muscle weakness from SMA feel worse.
4. Optimizing your overall health with lifestyle strategies cannot alter SMA, but it can help you minimize the risk of complications and improve your quality of life.

Floppy or weak arms and legs,Movement problems – such as difficulty sitting up, crawling or walking.
twitching or shaking muscles
Bone and joint problems – such as an unusually curved spine (scoliosis),Swallowing problems,Breathing difficulties
Nusinersen (Spinraza),Onasemnogene abeparvovec-xioi (Zolgensma),Risdiplam (Evrysdi)

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