Spinal muscular atrophy (SMA) is a genetic disorder that affects how a person can control their muscle movements.
Children with SMA have trouble controlling their muscle movement. This condition is caused by a loss of specialized nerve cells – called motor neurons – located throughout the spinal cord and in the part of the brain that is connected to the spinal cord (brainstem). That loss of motor neurons causes weakness and wasting (atrophy) of the muscles that children use for many activities, including crawling, walking, sitting up and controlling the head.
Spinal muscular atrophy is split into four types:
Type I spinal muscular atrophy – Also called Werdnig-Hoffman disease, this type is severe and diagnosed at birth or within the first few months of a baby’s life. Babies with this condition are developmentally delayed and have breathing and swallowing problems.
Type II spinal muscular atrophy – This type of spinal muscular atrophy generally begins between 6 and 12 months of age. Babies with this condition can sit without support, but may need assistance getting to the seated position. Individuals with this condition cannot stand or walk without assistance.
Type III spinal muscular atrophy – Also called Kugelberg-Welander disease, this is a milder type that usually begins to appear during early childhood (birth to 5 years*) or adolescence (10 to 19 years**). Individuals with this condition can stand and walk without assistance, but, over time, walking and climbing stairs can become difficult.
Type IV spinal muscular atrophy – This type occurs after age 30 and usually only affects the muscles close to the center of the body (proximal muscles), such as the upper arms and legs.
The signs and symptoms of spinal muscular atrophy vary according to the specific type an individual has. Possible symptoms include:
Breathing and swallowing problems
Difficulty sitting or reaching a seated position unassisted
Difficulty walking or climbing stairs
Inability to hold up the head
Tremors or twitching
Treatments and Care
SPINRAZA (nusinersen) is a new drug that has been developed to treat some types of spinal muscular atrophy. For more information about this treatment, please refer to this page.