Spinal Muscular Atrophy
Signs and Symptoms

Each child with spinal muscular atrophy (SMA) may experience symptoms differently. There are three main types of SMA, which are defined by their symptoms and the time symptoms first develop.

Acute Infantile SMA (Type I)

Also known as Werdnig-Hoffman disease, this form of SMA is the most severe. Some children develop the disease before birth. Mothers may notice that during the last three months of pregnancy, fetal movements are very weak. The majority of children with this form of the disease will experience symptoms before 8 months of age.

The condition primarily affects the muscles that control chewing and swallowing, chest wall muscles, and arm and leg muscles. Symptoms are typically severe and may include hypotonia or diminished muscle tone, muscle weakness, respiratory problems, pneumonia, and swallowing and feeding difficulties.

Quivering of the tongue, a condition called tongue fasciculation, also may occur. Children with this form of SMA face a difficult battle and many die from recurrent respiratory infections within the first year of life. However, with new therapies, some children live into their teens or early adulthood.

Chronic Infantile SMA (Type II)

This form of SMA is less severe than acute infantile and usually progresses slowly. Symptoms normally develop between 6 to 18 months of age.

Children with chronic infantile SMA may sit independently, but need support to walk or stand.

Other symptoms may include:

• Decreased or absent deep tendon reflexes, such as the relfex that occurs when you tap on your knee.
• Hypotonia or diminished muscle tone
• Involuntary contractions or twitching of muscles called fasciculations
• Respiratory problems

Some children may need a wheelchair and develop orthopedic problems, such as curvature of the spine called kyphoscoliosis.

Juvenile SMA (Type III)

This form of SMA is also known as Kugelberg-Welander disease. Symptoms normally occur between 2 and 17 years of age. The severity of the condition varies, but generally progresses slowly. Some children may not walk or stand on their own, while others do.

Children with this form of SMA rarely experience respiratory or swallowing problems, but may experience weakness in the shoulders, hips, thighs and upper back.

Reviewed by health care specialists at UCSF Benioff Children's Hospital.
Last updated February 7, 2012