Reviewed by: HU Medical Review Board | Last reviewed: August 2021
Most of the common types of SMA start during childhood. Fewer than 5 percent of all SMA cases are type 4 SMA. This is the most common type of adult-onset SMA. Symptoms appear during adulthood, usually after age 30. Symptoms include mild muscle weakness, tremor, and twitching.1,2
Type 4 SMA is on the mild end of the spectrum of SMA types. Adults can stand and walk independently. They usually keep the ability to walk throughout life.
Adults with this type of SMA have a normal life expectancy. Muscle weakness usually progresses very slowly and does not affect swallowing or breathing.1,2
It is normal to experience stress and anxiety during and after the diagnosis. You may be worried about how SMA will progress or how it will affect your daily life. Consider joining a support group or talking to a therapist to find ways to cope with a new diagnosis.
How is adult-onset spinal muscular atrophy diagnosed?
Diagnosis of adult-onset SMA may take a long time from when symptoms first appear. This is because mild muscle weakness and other symptoms are similar to other neuromuscular disorders.3
Once doctors suspect that you have SMA, they will order a blood test for the SMN1 gene. Most people with SMA can be diagnosed by a complete lack of the SMN1 gene.
If this test shows an absence of the SMN1 gene, you have SMA. Doctors may then test for the number of SMN2 copies you have. This can help determine the severity of SMA.4,5
If the blood test shows you have the SMN1 gene, you may have a condition other than SMA. Possibilities include spinobulbar muscular atrophy or a different adult-onset neuromuscular condition. Doctors may use other tests to determine a diagnosis, including:4,5
- Electromyography (EMG) to look at electrical activity of muscles
- Muscle biopsy
- Blood test for the muscle enzyme creatine kinase
What are ways to cope with a diagnosis during adulthood?
In general, those with type 4 SMA do not become severely disabled and can enjoy a high quality of life. However, every person with adult-onset SMA is different. Symptoms and motor function can greatly vary.
The process of getting a diagnosis can be stressful. Because of this, it is normal to have anxiety about how SMA will affect your life.3,5
Some common worries of adults with type 4 SMA include:3
- Future loss of movement and mobility
- Loss of independence
- How SMA will affect your relationships and career
- Navigating the healthcare system
- How SMA will affect your hobbies, such as physical activities or traveling
- Other family members having SMA, especially future children
Ask for help from friends, family, or other supportive people. Talking to other people with adult-onset SMA can help learn how they handled life changes after an SMA diagnosis.
Talking to a therapist or counselor can also be helpful. They can help identify what is causing you anxiety and suggest ways to cope. Some common ways to cope with an SMA diagnosis include:
- Learning as much as possible about SMA and its treatments
- Asking your doctors questions
- Asking for help from family and friends
- Joining a support group
- Talking to a genetic counselor
- Finding hobbies and practicing self-care
- Communicating openly with loved ones, partners, and employers