Imagine a condition that gradually weakens the muscles you rely on every day to walk, run, and lift your arms. This is the reality for those with Kugelberg-Welander disease, a type of spinal muscular atrophy (SMA) also known as juvenile SMA, Kugelberg-Welander syndrome, or SMA type 3. This inherited neuromuscular disorder causes muscles to lose strength over time, often beginning in childhood or adolescence, affecting mobility and physical activities.

Kugelberg-Welander disease typically causes symptoms including hypotonia (muscle weakness) in the arms and legs and difficulty walking, running, and using stairs. Hand tremors, poor weight gain, and insufficient growth are also associated with the condition. Without proper care, people with SMA type 3 can develop lung disease, scoliosis, and joint contractures.

Kugelberg-Welander disease is one of five main types of SMA, which include SMA 0 through SMA 4. Symptoms for type 3 are less severe than those of types 0, 1, or 2. Kugelberg-Welander disease usually develops in early childhood and adolescence. The condition progresses more slowly than SMA type 1 or type 2, which have an earlier onset. People with type 3 SMA have a normal life expectancy.

Learn more about the various types of SMA.

The History of Kugelberg-Welander Disease

Kugelberg-Welander disease was named after Eric Kugelberg and Lisa Welander, Swedish neurologists and mycologists (scientists who study fungi) who researched the brain and muscles. The disease was first described in a research article in 1956. A neurologist named Gunnar Wohlfart also participated in the research, so the condition is sometimes called Wohlfart-Kugelberg-Welander disease.

Physicians Guido Werdnig and Johan Hoffman first discovered progressive SMA in 1891. The condition was originally called Werdnig-Hoffmann disease, a name still used for SMA type 1.

Kugelberg and Welander discovered that the age of onset for SMA can determine different outcomes of the disease. The earlier a person develops SMA, the worse their outcome will be, due to the muscle and nerve deterioration during earlier stages of development.

Connecting the Dots Through Genetics

A breakthrough occurred in 1995 with the discovery of the survival motor neuron gene (SMN1). The SMN1 gene helps motor neurons survive by encoding a particular protein. A mutation (change, or variant) of this gene causes 95 percent of SMA cases. In 1999, researchers made a second important discovery, the SMN2 gene. The number of copies of this gene a person has can influence how severe their SMA will be.

The discovery of the SMN1 and SMN2 genes led to genetic testing for SMA. Although terms for the disease like Kugelberg-Welander are still used, clinical designations for SMA are now structured by types, based on the age that symptoms of the disease first occur.

• SMA type 0 (severe) — Starts before birth
• SMA type 1 (severe) — Appears in newborns
• SMA type 2 (intermediate) — Develops between 3 and 15 months of age
• SMA type 3 (mild) — Begins between 18 months through early adulthood
• SMA type 4 (mild) — Shows up in adulthood

Read more about the causes of SMA.

SMA Treatment Breakthroughs

The discovery of the SMN genes has opened up new avenues of research in the treatment of SMA. In December 2016, nusinersen (Spinraza) became the first drug approved by the U.S. Food and Drug Administration (FDA) for treating SMA. Nusinersen targets abnormalities in the SMN2 gene to stabilize the survival motor neuron protein.

Nusinersen is given by an intrathecal injection (into the spine) through the lower back and requires ongoing doses at a hospital or specialized medical center. Forty percent of people treated with the drug experience positive results, including slower progression of the disease and improved motor function and muscle strength.

New drugs for treating SMA continue to be developed and tested in clinical trials. In 2020, the FDA approved risdiplam (Evrysdi), which also targets the SMN2 gene. Risdiplam can be taken orally or through a feeding tube. It’s the first SMA drug that can be given at home.

Onasemnogene abeparvovec-xioi (Zolgensma) approved by the FDA in 2019, is the first drug to target and replace the SMN1 gene. It’s currently used only for some young children and infants under 2 years of age.

Talk to Your Doctor

Recent advances in genetic research have led to new treatments that can help manage symptoms and improve daily life. If you or a loved one has been diagnosed with SMA type 3, talk to your doctor about the best treatment options and support available. Continued research is bringing hope to those living with this condition.

Find Your Team

On mySMAteam, the social network for people with spinal muscular atrophy and their loved ones, more than 2,600 members come together to ask questions, give advice, and share their stories with others who understand life with SMA.

Do you have any tips for people with type 3 SMA? Have you tried Spinraza or Evrysdi? Share your experience in the comments below, or start a conversation by posting on your Activities page.